CAR VIBRATES AT HIGH SPEEDS

SYMPTOM SUMMARY
There is a vibration or shimmy at high speeds. The symptom may get worse as the vehicles speed increases and may or may not be present at lower speeds.

USUAL CAUSE The usual cause of a vibration or shimmy at high speed is improper tire balance or damaged tires.

DIAGNOSIS
Perform a careful visual inspection of each tire. Look for damage to the tires such as bulges or exposed steel belts. Inspect the wheels for dents, warpage or missing lug nuts. Check the tire pressure to ensure all tires are inflated evenly and to the correct pressure (check the owner's manual for the correct tire pressure - it should also be marked on the side of the tire). If the tires are in good condition, the most cost effective diagnosis is to have the tires computer spin balanced. This can be done at any tire retailer for a nominal charge. If the problem still persists, further diagnosis on the drive train should be performed. On rear wheel drive vehicles the U-Joints should be inspected. On front wheel drive vehicles, the drive axles and CV Joints should be inspected. Inspect the CV boots for tears or other damage indicating excessive joint wear.

PRECAUTIONS, TIPS, and NOTES Tires contain steel belts that, if exposed, are very sharp and can cut or cause injury to your skin. To prevent possible injury to your hands, do not run your hand over the tire during inspection.

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BRAKE WARNING LIGHT IS ON

SYMPTOM SUMMARY
The red brake warning lamp remains on after the vehicle is started.

USUAL CAUSE
The brake system is equipped with a red brake warning lamp that will illuminate under certain conditions. Some vehicles feature a float located in the master cylinder that will illuminate the brake warning lamp when the fluid level becomes too low. The light will also come on if hydraulic pressure is lost in one of the front or rear brake channels. Usually the proportioning valve contains the circuit that will turn the light on during hydraulic pressure failure. It will also automatically prevent any additional fluid to be routed to the leaking channel. This ensures there is an adequate brake fluid and pressure supply to the working channel. The light usually functions as the parking brake indicator lamp as well.

DIAGNOSIS
The first step in diagnosing this symptom is a visual inspection. Check the brake fluid level in the master cylinder to ensure it is within specifications. If the brake fluid level is low, you will need to inspect the system for leaks. You may refer to the "Brake Fluid Consumption" symptom for further details on the diagnosis of brake fluid loss. Ensure the emergency brake is completely released. On most vehicles, the emergency brake circuit will illuminate the bulb at a different intensity than the fluid level or pressure sensors. If the brakes function normally and have been inspected and found to be leak free, you should suspect a malfunction in the emergency brake light circuit. Apply and release the emergency brake and look for a change in the bulbs intensity. If no change occurs, this further confirms a malfunction in the emergency brake light circuit. This switch is usually located on the emergency brake mechanism and should be inspected for damage.

PRECAUTIONS, TIPS, and NOTES
Always use the proper brake fluid DOT rating when refilling or adding to the brake fluid master cylinder. Do not add more than 1 oz of fluid to the master cylinder without inspecting the system for leaks.

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MASTER CYLINDER IS LOW ON BRAKE FLUID

SYMPTOM SUMMARY
The master cylinder is low on brake fluid or the brake fluid continually goes low.

USUAL CAUSE
It is normal for the master fluid level to decrease slightly as the brake pads wear. As the brake pads wear, the pistons in the caliper extend to compensate for the friction wear. As this occurs, the caliper will store more brake fluid in the caliper cylinder and will decrease the fluid level in the master cylinder.

DIAGNOSIS
You will need to determine whether the fluid level is low in the master cylinder due to a fluid leak or the normal brake pad wear discussed above. A brake inspeciton should be performed to determine the cause. The calipers, wheel cylinders (on drum brakes) will need to be inspected. The brake pads and shoes (if equipped) should be inspected for signs of brake fluid contamination indicating a leak. Inspect the calipers for leaks at the rubber dust boot around the pistons. The dust boot on the wheel cylinder will have to be pulled off slightly to inspect for leaks. Check the hydraulic lines, proportioning valve and flexible hoses for leaks. Inspect the master cylinder where it mounts on the brake boosters for signs of leaks. Loosening the master cylinder retaining bolts and pulling it back slightly, will usually result in detection of a leak if present. If leaking, the fluid will run out of the mating surfaces. In this case, the master cylinder will require replacement. If there are no leaks present and the pads are worn, the most likely cause of the low brake fluid level is worn brake pads.

PRECAUTIONS, TIPS, and NOTES
The brake fluid level should be inspected at every oil change. If servicing the hydraulic system, use caution not to contaminate the system with dirt, debris or water. After the hydraulic system is serviced it will require bleeding. Refer to the manufacturers bleeding procedure to ensure all of the air is purged from the system. Always use the recommended brake fluid DOT rating. This information can be obtained from your owners manual or off the cap on the master cylinder.

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LOUD SQUEAL HEARD WHEN STEERING WHEEL IS TURNED

SYMPTOM SUMMARY
A loud squeal is emitted from under the hood when the steering wheel is turned.

USUAL CAUSE This symptom is usually caused by a loose or worn power steering belt.

DIAGNOSIS
With the help of an assistant, rotate the wheel all the way to the right or left while inspecting the drive belts. If the drive belts slip or squeal, service will be necessary. With the vehicle off, inspect the belts for wear or cracking. Some vehicles utilize a single serpentine belt that drives all of the accessories. These types of belts usually use an automatic tensioner that maintains the proper tension at all times. Inspect the belts for proper alignment to the pullies. A worn tensioner bearing can throw the belt out of alignment, causing abnormal belt wear or breakage.
Vehicles that use conventional "V" belts should be inspected for cracks or glazing. Over time, the inside surface of the V-belt can become glazed which can cause it to slip. A glazed belt will have a shine to it and feel hard and brittle. The tension of the V-belt should have about a 1/2" of deflection between its longest span. Over tightening a V-belt can lead to bearing failure in the driven accessory. Drive belts that are worn should be replaced and properly tensioned.

PRECAUTIONS, TIPS, and NOTES
Some vehicles use automatic tensioners that contain a large spring used to tension the drive belt(s). You should use caution when removing the belt from the tensioner. The tensioner can snap if not carefully held in place causing injury to your hands or arms. Always use caution when working under the hood. Some parts become very hot and can burn if touched. Rotating engine parts should be avoided by your body and loose clothing. Entanglement can cause severe injury.

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THERE IS A LIQUID ON THE FLOORBOARD OF MY CAR

SYMPTOM SUMMARYThere is a liquid present on the floorboard of the vehicle. The fluid may be green or clear and may be more noticeable after operating the heating or air conditioning system.

USUAL CAUSE Water present on the floorboard is usually caused by one of two things. Water is circulated into the passenger compartment through the heater core. The heater core is heated by the engine coolant. Air is then blown over the heater core, by the blower motor when the heater is on, to heat the passenger compartment. If this core develops a leak, it will usually leak into the passenger compartment floorboard. A heater core that has only a pin-hole sized leak, may not be leaking on the floor but may produce a fine mist or oily film that collects on the inside of the windshield. The evaporator core is also located in the same housing as the heater core. During normal air conditioning operation water will condense on the core. This water is normally drained out of the passenger compartment through a evaporator drain hose. The hose connects from the evaporator case inside the vehicle to the exterior of the vehicle at the rear of the engine compartment. If this hose becomes restricted, the water that condenses on the evaporator core will leak into the passenger compartment. This is usually clean water that will evaporate as opposed to coolant that will not evaporate and leave an oily film on the floorboard carpet.

DIAGNOSIS
You should verify the type of leak present. The heater core contains coolant that will feel oily and may have a green color to it. Water from the evaporator core will be clear with no color. Taking a white piece of paper and absorbing some of the fluid may help determine the fluid type.

CORRECTIVE ACTION
The only corrective action for a leak in the heater core is replacement. Do not use radiator stop leak or other sealant products in an attempt to fix a leak in the heater core. If the fluid is clear, the evaporator drain tube may be restricted or plugged. This hose is usually visible at the lower rear of the engine compartment on the right (passenger) side of the vehicle. You can inspect and/or clear the blockage by passing a piece of stiff wire through the end of the hose.

PRECAUTIONS, TIPS, and NOTES
A heater core that is leaking cannot be repaired and must be replaced. On most vehicles, replacing the heater core is an extensive and time-consuming project that may require special tools. The evaporator core that contains the refrigerant (Freon) for the air conditioner may be contained in the same housing as the heater core. On these vehicles, the housing is removed as a single unit and requires the refrigerant to be removed from the air conditioning system using special equipment. You should consult a repair manual specific to your vehicle or consult the advice of a professional technician prior to undertaking this job.

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FRONT END DIPS WHEN I STEP ON THE BRAKES

SYMPTOM SUMMARY
The vehicle dips forward when the brakes are applied.

USUAL CAUSE This symptom is usually caused by misadjusted rear brakes or weak shocks or struts.

DIAGNOSIS The shocks or struts can be tested by bouncing the front of the vehicle several times by placing your body weight on the front bumper. Once the vehicle starts the up and down motion, remove your weight from the front bumper. The up and down bouncing should come to a stop after only one or two additional bounces. If the the vehicle continues to bounce, the front shocks or struts may require replacement. A tire inspection can reveal worn shocks or struts as well. Bumps and dips accross the tread of the tire can indicate failed shocks or struts. If the shocks or struts are in good working order, the rear brake adjustment should be inspected. Inspect the parking brake to make sure it holds. If it does not hold, operate it several times. This will adjust the rear brakes on vehicles with self adjusters. If the parking brake still does not hold, a visual inspection of the brakes will be necessary to determine the cause.

PRECAUTIONS, TIPS, and NOTES Brake drums and rotors become extremely hot after vehicle operation. Use caution when working around hot braking components.

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CAR PULLS WHEN I STEP ON THE BRAKES

SYMPTOM SUMMARY
The vehicle pulls to the right or left when the brakes are applied.

USUAL CAUSE The usual cause of this symptom is contamination on the braking surface or a malfunctioning caliper. It can also be caused by different tire sizes on the right and left wheels. Worn suspension components can also cause this symptom.

DIAGNOSIS
If contamination, such as grease or oil is present on the left side, the vehicle will pull to the right since the left side will not provide the same braking force as the right. A visual inspection is the first step in diagnosing the problem. Perform a visual inspection on both sides of the vehicle. Check the following:

1. Inspect the tires for even tread wear and overall condition. Check to ensure tire inflation is the same and to specifications.

2. Inspect the brake rotors for contamination. On front wheel drive vehicles, inspect the CV boots for tears. If torn, the CV boot can allow the grease to contact the brake rotors.

3. Check the brake pads to ensure they are worn evenly on both sides of the vehicle. If one side is worn excessively, it could be caused by a sticking brake caliper. The brake caliper can slide or the pistons can stick, causing the brake caliper to maintain braking force on the caliper. This might be accompanied by a discolored brake rotor as well. Rotation of the wheels by hand with the vehicle on jackstands should be even on each side. On front wheel drive vehicles, the transmission should be placed in neutral. Ensure the emergency brake is engaged and proper jacking procedures are used. A wheel that requires excessive force to rotate by hand should be investigated further.

4. Inspect the rubber brake hoses that connect to the calipers. A collapsed brake line can expand under pressure, allowing the brake fluid to enter the caliper then collapse trapping the brake fluid in the caliper.

5. With the vehicle jacked up and the tires on, inspect the front end components for excessive wear. With one hand on the front of the tire and one on the wheel, try to turn the wheel right and left (as if in a turn, not rotational). The wheel may be able to be turned to the right or left, but it should be tight and have no free play back and forth. Perform the same test with one hand on the top and one on the bottom of the tire. With your hand on the top, pull out while pushing in with the hand on the bottom. Then do the opposite, pull out on the bottom and in on the top. There should be no play in the wheel. If play is present in both of the above tests, it is usually an indication of a worn wheel bearing. If there is only play from right to left, it is usually an indication of a worn suspension component such as a tie rod end or rack and pinion. Perfoming the test while inspecting the front end will usually reveal the worn component.

PRECAUTIONS, TIPS, and NOTES Brake rotors become extremely hot during braking. Use caution when working on the brakes shortly after vehicle operation. Always refer to manufacturers jacking procedures to prevent damage to the vehicle or injury to yourself.

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BRAKE PEDAL PULSATES WHEN I STEP ON IT

SYMPTOM SUMMARY
The brake pedal pulsates when applied. The symptom may be worse at higher speeds.

USUAL CAUSE
This symptom is usually caused by warped brake rotors. If the vehicle is equipped with four wheel disc brakes, it could be either the front or rear brake rotors. Excessive heat build up on the brake rotors can cause them to warp , causing a brake pedal pulsation. This can be the result of heavy stop and go driving. If the rear brakes are not adjusted properly, the demand on the front brakes will be higher which can also contribute to front rotor warpage. Some vehicle brake designs are also more prone to warpage than others. A warped brake rotor will cause the piston in the brake caliper to pulsate in and out when the brakes are applied. This in turn, causes the hydraulic brake fluid to transmit this pulsation to the master cylinder, then to the brake pedal.

DIAGNOSIS
If the symptom only occurs during braking and is worse at higher speeds, the most probable cause is warped brake rotors.

CORRECTIVE ACTION The corrective action is to replace or have the rotors machined (often referred to as surfaced or turned). It is recommended that the brake rotors be machined during replacement of the brake pads. This provides a parallel flat mating surface to the new pads. If the rotors are being machined to correct the pulsation, it is also recommended that the pads be replaced unless there is more than 50% life left on the existing pads.

PRECAUTIONS, TIPS, and NOTES
Brake rotors become extremely hot after vehicle operation and braking. Use caution when working on the braking system. Brake rotors have a manufacturers minimum thickness. Never machine a rotor beyond the minimum thickness. This will only contribute to additional warpage, since the rotor cannot adequately dissipate the heat generated during braking. The minimum thickness is usually stamped on the brake rotor, usually on the back side. The brake rotor should be replaced once it has reached or has become thinner than its minimum thickness.

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THE BRAKE PEDAL GOES TO THE FLOOR WHEN I STEP ON IT

SYMPTOM SUMMARY
The brake pedal goes to the floor when pressed. There may be little or no braking action when the pedal is depressed. The Red Brake Warning Lamp may be illuminated indicating a system failure.

USUAL CAUSE
Very low brake fluid or a defective Master Cylinder is the usual cause of this symptom. The master cylinder pressurizes the brake system when the pedal is depressed and provides hydraulic fluid to each of the wheels to apply the brakes. The braking system is designed to illuminate the Red Brake Warning lamp when a hydraulic failure is present.

DIAGNOSIS
If you have just performed other brake work on the vehicle and the hydraulic system was opened, the most probable cause is air in the system. The system will need to be bled according to manufacturers recomendations. The first step in diagnosing this symptom is to inspect the brake fluid level at the master cylinder. If the fluid level is low, the system will need to be inspected for leaks. The calipers, wheel cylinders (on drum brakes) will need to be inspected. Brake pads that are completely worn can cause low fluid level. This is a result of the caliper pistons being completely extended, causing most of the brake fluid to reside in the calipers. The brake pads and shoes (if equipped) should be inspected for signs of brake fluid contamination indicating a leak. Inspect the calipers for leaks at the rubber dust boot around the pistons. The dust boot on the wheel cylinder will have to be pulled off slightly to inspect for leaks. Check the hydraulic lines, proportioning valve and flexible hoses for leaks. Inspect the master cylinder where it mounts on the brake booster for signs of leaks. Loosening the master cylinder retaining bolts and pulling it back slightly, will usually result in detection of a leak if present. If leaking, the fluid will run out of the mating surfaces. In this case, the master cylinder will require replacement. If there are no fluid leaks present or the fluid level is normal and the brake pads and shoes (if equipped) are in good condition, the most probable cause of the symptom is a defective master cylinder.

CORRECTIVE ACTION Determining the cause of the failure will dictate what corrective action is necessary. If the hydraulic system needs to be serviced, as with replacement of the master cylinder, it will need to be bled of all the air once it has been resealed. Refer to the manufacturers specific bleeding procedures.

PRECAUTIONS, TIPS, and NOTES
If the vehicle is equipped with ABS, certain ABS components can cause this symptom. In this case, the system should be serviced according to manufacturers recommendations. If servicing the hydraulic system, use caution not to contaminate the system with dirt, debris or water. Always use the recommended brake fluid DOT rating. This information can be obtained from your owners manual or off the cap on the master cylinder.

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BRAKES MAKE A GRINDING NOISE WHEN APPLIED

SYMPTOM SUMMARY
The brakes emit a grinding noise when applied. The braking action may not be as effective as normal.

USUAL CAUSE This symptom is usually caused by metal to metal contact between the brake pad and rotor or brake shoe and drum. The brake pads and shoes have a metal surface that the friction surface is mated to. Once the friction material is worn off, the metal surface will contact the rotating surface of the drum or rotor. This metal to metal contact usually results in a grinding noise.

DIAGNOSIS A visual inspection of the brake system will indicate the cause of the noise. The brake pads and rotors should be inspected for damage. If the rotor is excessively worn beyond the manufacturers minimum thickness, the rotor will have to be replaced. If the drums have grooves worn in them beyond the manufacturers maximum diameter, they will require replacement.

PRECAUTIONS, TIPS, and NOTES When replacing the brake pads or shoes, it is recommended that the brake rotors and drums be machined (often referred to as surfaced or turned). This will provide a flat mating surface for the new pads or shoes which will prevent brake squeal. A high quality anti-squeak compound should be applied sparingly to the back side of the new pads. Some vehicles use metal shims between the pad and the caliper. These shims should be replaced or cleaned and re-installed. Brake rotors and drums become extremely hot after vehicle operation and braking. Use caution when working on the braking system. Brake rotors and drums have a manufacturers minimum thickness and maximum diameter specifications. Never machine a rotor or drum beyond the manufacturers specifications. The minimum thickness and maximum diameter specification is usually stamped on the brake rotor or drum.

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ODOR COMING FROM AIR CONDITIONING VENTS

SYMPTOM SUMMARYA mild to severe odor that emanates from the air conditioning vents shortly after starting the air conditoning. The odor may diminish after the air conditioner has been running for several minutes but reoccurs at next operation.

USUAL CAUSE Odor from the air conditioning is usually caused by mildew growth on the air conditioning evaporator core. During normal A/C operation, water condenses on the evaporator core. This water is drained off through a tube located at the bottom of the evaporator housing in the passenger compartment. Small amounts of water will remain on the evaporator core after the air conditioning is turned off. On a hot day, this moisture inside the evaporator case can cause mildew growth on the evaporator core. This mildew growth can cause a foul odor through the air conditioning vents during the first few minutes of air conditioning operation. It can smell like dirty feet or stinky socks.

CORRECTIVE ACTION
There are several industrial chemicals that can be used to kill the mildew growth, but it will usually require perodic treatments at the peak of the air conditioning season. Household mildew sprays can also help by spraying a fine mist into the vent inlets, usually located on the exterior of the vehicle near the windshield. This procedure should be done while the fan is on high, all windows in the vehicle open and the recirculation switch on the dash set to outside air. The purpose is to draw the cleaner past the evaporator core killing any mildew present on the surface. Use the cleaner sparingly and never spray it directly into the vents located in the passenger compartment.

PRECAUTIONS, TIPS, and NOTES
Completely ventilate the vehicle of any cleaner fumes prior to driving with the windows up. Use caution with the cleaner not to damage the paint or interior of the vehicle.

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ANTI-LOCK BRAKE LIGHT STAYS ON AFTER ENGINE IS STARTED

SYMPTOM SUMMARY
The "ABS" or "Anti-Lock Brakes" light remains on after the engine is started and remains on or flashes.

USUAL CAUSE
The Anti-Lock brake system is designed to rapidly modulate the braking action during a panic stop. This prevents the wheels from locking up and maintains vehicle control and stability. An ABS control module monitors the wheel speed and other various sensors to determine when wheel lock-up is about to occur. The ABS module continually performs diagnostics to ensure that the system is functional. When a malfunction occurs, the ABS module will illuminate or flash the ABS or Anti-Lock light on the dash panel to alert the driver. During start up, the module will illuminate the light as a self test. Shortly after the engine is started, the light should go out indicating the system is functional. If the light remains on the ABS Module has detected a system failure. On most vehicles, the ABS system will not be functional while the light is illuminated. Usually, normal braking will result unless the failure is related to a component that is used for both normal braking and anti-lock braking. If the Red Brake light is also on, normal braking may be degraded as well indicating a system wide failure.

DIAGNOSIS
On almost all ABS systems the module will store a diagnostic trouble code that relates to the circuit or component that has failed. The diagnosis will require the module to be placed in self diagnostic mode, which will result in it transmitting the stored diagnostic code. Once the code is received, the diagnosis should focus on that particular component or sensor. A vehicle specific service manual will indicate how the module is placed into diagnostic mode and will indicated what circuit or component relates to what code. Often a special scan tool, similar to a hand held computer, is required to interface with the module.

CORRECTIVE ACTION Once the code has been retreived from the modules memory, that component or circuit will require service. Some components, such as the wheel speed sensors, are usually simple to replace. However, other components such as the hydraulic modulator and control solenoids require special tools and special bleeding procedures to ensure proper operation.

PRECAUTIONS, TIPS, and NOTES
If the ABS light is on, the failure should be corrected as soon as possible. If possible, you should leave repairs to the ABS system to trained service personnel that are equipped with the correct tools and equipment. The Hydraulic Modulator may contain brake fluid pressurized to over 1,500 psi, that if not properly bled, can pose significant danger to someone servicing the system.

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THE TORSION BAR

TORSION BARS
Torsion bars provide spring action for the front suspension from the twisting of a metal bar. Torsion bars are anchored to the frame at one end and attached to the lower control arm at the other. The weight of the vehicle along with the movement of the control arm causes the rod to twist. The twisting of the metal rod provides a torsional spring that reacts in a similar manner to the coil spring. Ride height is controlled through use of an adjustable arm at the frame mounting point for the torsion bar.

AUTOMATIC LEVEL CONTROL
Automatic level control provides automatic adjustment of a vehicles ride height to compensate for load or driving conditions. Components consist of a level controller, air pump, air shocks or air bags and ride height sensors. The system works by using sensors to input information about the ride height of a vehicle to the controller. The controller then supplies air from the air pump to the air shocks or air bags, as necessary to adjust the vehicles ride height as needed.

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SUSPENSION AND TIRES

SUSPENSION OVERVIEW
The suspension of a vehicle is used to allow the tires to react to changes in the road surface and support the chassis of the vehicle. The suspension allows the wheels to move up and down while dampening the transfer of this movement to the rest of the vehicle, including the occupants. Independent suspension is used in the front ends of passenger cars and most light trucks. Some vehicles use four wheel independent suspension. Independent suspension allows one wheel to react to surface variation without affecting the other wheels. Each wheel is attached to the chassis using individual suspension components.

TIRES
The tires of an automobile provide traction for starting, stopping and driving. They are used to support the weight of a vehicle and as an aid to the operation of the vehicles suspension. Passenger car tire sizes in the U.S. today, are rated in the P-Metric system. The rating can be found on the side wall of the tire. This is an alpha-numeric rating system that uses a letter or number to represent size, usage or construction of a tire. An example is P215/75R15. The first letter is an indication of the usage of the tire, P would stand for passenger car, LT would be a light truck. 215 is a rating in millimeters for the section width of a tire. The number after the slash represents the aspect ratio of the tire and the tires sidewall height in relation to its width. The R designates the construction of the tire, in this case it stands for radial. If a letter were to preceded this letter, it would indicate a speed rating of the tire. The last number indicates the rim size that the tire is intended for.

Other information that can be found on the tire side wall is the Uniform Tire Quality Grading designation. This is a government tire rating system used by manufacturers to provide tire comparison information. With the UTQG rating system, information is given to compare tire treadwear, traction and temperature resistance. Treadwear is a measure of tire durability. 100 would be a tire rated for standard resistance to treadwear. A rating of 300 would be a tire with three times the treadwear resistance of a standard tire. This rating should be used to compare tire treadwear within a manufacturer, not between manufacturers.

The traction rating is a grade classifying a tires ability to stop in a straight line on wet surfaces, concrete and asphalt under test conditions. An A rating means the tire meets maximum DOT standards. A B rating means the tire meets medium DOT requirements. A C rating indicates a tire meets minimum requirements. There are three grades used to measure a tires resistance to generation of heat due to friction. Grade A indicates a tire that can withstand temperatures generated at 115 mph for 30 minutes. Grade B indicates a tire that can withstand temperatures generated at 100 mph for 30 minutes. Grade C indicates a tire that cannot withstand temperatures generated at 100 mph for 30 minutes.

Tire wear is affected by driving conditions, wheel alignment, balance and inflation pressure. Proper maintenance is the best way to insure longer tire life. Inflation pressure should be checked weekly. Tire rotation schedules should be followed as recommended by the manufacturer. Wheel alignment should be checked if uneven tire wear is noticed or after running over a large hole or object. Aggressive driving should be avoided to extend tire life as well.

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STEERING SYSTEM OVERVIEW

POWER STEERING PUMP
The power steering pump provides the hydraulic pressure used for steering assistance. The power steering pump is driven by a belt attached to the crankshaft pulley. The power steering pump pulley rotates a vane assembly inside a pump ring located inside the pump. Pressure is created by compressing fluid between the vanes and the surface of the pump ring. The pump pressure output is maintained by a flow control valve that contains an internal pressure relief valve. There are two types of power steering pumps used, submerged and nonsubmerged. Both are similar in operation, with the only difference being the type of fluid reservoir used. A submerged type of pump contains the pump and fluid reservoir in one unit. A nonsubmerged uses a remote fluid reservoir for the pump.

STEERING COLUMN/SHAFT
The steering column is a link between the steering wheel and the steering gear. It consists of a collapsible housing containing a collapsible rotating shaft. As a safety measure, the steering column is designed to collapse in the event of a front end collision. If a steering column has collapsed, it must be replaced. The steering shaft is a two piece component located inside the steering column. It is supported at the top and the bottom of the steering column by bearings. The steering column housing may also contain transmission shift components. Design of transmission shift components can vary from model to model. Earlier models use a tube that contained a rod that runs the length of the column used to actuate shift linkage. Recent model vehicles use a cable operated shift linkage, that can be actuated by a column mounted shift lever. Safety designs on late model vehicles incorporate a brake transmission shift interlock system. This system locks out shifter operation, when the ignition is on, until the brake pedal is depressed. Most systems use an electric solenoid actuated by the brake light switch, that releases the shift linkage. The steering column is used to mount several accessories. The turn signal switch, headlamp dimmer switch, wiper switch, and ignition switch, can be located on or inside the steering column. Service of the steering column usually requires removal of these components. Care should be taken when the steering column is removed for service. The column should not be dropped, leaned on, or subject to blows to either end. Internal components of the column can shear off, causing the column to partially collapse.

TIE RODS
The tie rods are used to link the steering gear to the steering knuckle. The tie rod ends are a ball and socket design that allows the tie rod to flex up and down with the movement of the front suspension. Tie rods should be inspected for excessive movement, grease seal tears, or any visible wear. You should not be able to collapse the ball and socket assembly of the tie rod by attempting to compress it by hand. Any inward movement of the ball and socket should be considered excessive wear.

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CONTROL ARMS Et STEERING KNUCKLES

STEERING KNUCKLES
The steering knuckle provides an attachment point for the tie rod to the wheel. The steering knuckle also provides an attachment point for the upper and lower ball joints in conventional A frame suspension system. With Macpherson strut systems, the steering knuckle anchors the lower end of the strut and the lower ball joint. The spindle of a rear wheel drive vehicle is supported and attached by the steering knuckle. With a front wheel drive vehicle, the front hub and bearing assembly is attached to the steering knuckle. Disc brake systems also use the steering knuckle as a mount for the brake caliper. The components attached to the steering knuckle will usually wear out before the steering knuckle itself. In fact, most of the damage to a steering knuckle will occur from collision damage.

CONTROL ARMS
Control arms, commonly referred to as "A Arms", provide a flexible attachment point for the suspension components to the frame of a vehicle. Vertical movement of the control arm is allowed through the use of bushings placed in the end of the control arms at the attachment point to the frame. In a conventional front suspension system, the lower control arm is attached to the frame and provides support for the bottom of the coil spring. The upper control arm is attached to the frame and flexes up and down in unison with the lower control arm. The upper and lower control arms are both attached to the steering knuckle by the upper and lower ball joints. Only the lower control arm is used in a vehicle equipped with Macpherson struts. The upper end of the strut provides support for the vehicle suspension and also acts as a swivel for the steering knuckle. The lower control arm attaches to the frame using a bushing to enable it to swing up and down. The lower control arm attaches to the steering knuckle using the ball joint and will flex up and down in unison with the strut. Wear of the control arm is usually confined to worn control arm bushings and can cause a knocking noise to emanate from the front end when braking or accelerating. Wheel alignment can also be affected.

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STEERING HUB

The hub and bearing assembly is attached to the spindle and steering knuckle of a vehicle's front suspension. The hub and bearings provide a rotation point for the wheel, as well as support for the weight of the vehicle on the spindle or axle. Rear wheel drive vehicles use tapered roller bearings for the front wheels. The wheel bearings are placed in the hub with the tapered ends facing one another. The inner bearing is larger than the outer bearing due to the need for increased support for the wheel. The outer races of the wheel bearings are pressed into the hub assembly. The wheel bearings are lubricated with bearing grease and are completely serviceable. Bearing preload (the tightness) is set with the hub retaining nut. The hub retaining nut is secured to the spindle and torqued to a specified setting and is secured using a cotter pin.

Front wheel drive vehicles generally use sealed roller bearings pressed into the hub. These bearings are usually only serviced as an assembly and since they are sealed, require no maintenance. Some front wheel drive bearing designs use tapered roller bearing assemblies. This type of wheel hub design is generally a press fit and bearing preload is set using spacers.

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SQUEAK OR SQUEAL FROM WHEEL

SYMPTOM SUMMARY
There is a squeak or squeal sound coming from the wheel area when the vehicle is in motion. The symptom may be worse when the brakes are applied.

USUAL CAUSE
A squeak or squeal from the wheel area can be caused by worn brake pads or uneven braking surfaces between the pad and the brake rotor. The brake pad is equipped with a metal wear indicator that contacts the brake rotor when the pads become worn beyond their useful service life. This wear indicator is designed to emit a high pitched squeak when it contacts the brake rotor to indicate that brake service is needed. If the brakes are severely worn, the indicator may contact the rotor at all times emitting the squeak even when the brakes are not applied.

DIAGNOSIS
A visual inspection of the brakes will indicate if brake service is necessary. If the pads are worn to the wear indicator, replacement will be necessary. If the pads still have a useful service life left, an anti-squeak compound may be applied to the backside of the pad (metal side).

PRECAUTIONS, TIPS, and NOTES
When replacing the brake pads, it is recommended that the brake rotors be machined (often referred to as surfaced or turned). This will provide a flat mating surface for the new pads which will prevent brake squeal. A high quality anti-squeak compound should be applied sparingly to the back side of the new pads. Some vehicles use metal shims between the pad and the caliper. These shims should be replaced or cleaned and reinstalled. Brake rotors become extremely hot after vehicle operation and braking. Use caution when working on the braking system. Brake rotors have a manufacturers minimum thickness. Never machine a rotor beyond the minimum thickness. This will only contribute to warpage since the rotor cannot adequately dissipate the heat generated during braking. The minimum thickness is usually stamped on the brake rotor, usually on the back side. The brake rotor should be replaced once it has reached or has become thinner than its minimum thickness.

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Squealing Sounds

General Description of Problem:
You hear a squealing sound at some point during the operation of your vehicle.

Probable Explanation:
Most squealing in an automobile comes from one of two locations. These are the belts or the brakes. Typical squealing from under the hood occurs when belts are slipping while brakes often squeal when either engaged in stopping or when the pads are worn to a low level and the "Warning Sensor" squeals to notify you it is time to get your brakes replaced.

Solutions:
1. Determine if the squeal is under the hood or in the brake system. Common under the hood squeals can be heard immedietely after starting the car as the various belts kick into action, during use of the A/C system, or while turning in a car with power steering. If the squeal is only noticeable while braking, or is only heard while the car is in motion but disappears when braking, the squeal is likely from the brake system.

2. Once you have determined the belt that is the cause of your squeal, you will need to check it for tightness, and replace if it is worn. As mentioned above, common belts that squeal are the power steering belt if you hear the noise during turns, and the A/C belt if the noise is noticeable only when the A/C is on. Other belts to consider are the alternator belt if you hear the sound under load or acceleration, or if under idle it may be the timing belt.

3. If the noise is not coming from the belts, you will want to determine wheteher the sounds from the brake system are during stopping, or during travel. If you hear the squeal only when applying the brakes, this may be an annoyance more than a problem. If you depress the pedal lightly and hear a faint squale, you can likley obtain some anti-squeal brake paste to apply to the pads to minimize the noise. If you get the squeal when braking hard as well, you may need a different type pad or lining than what is currently installed. If you notice the noise while driving and it disappears when you step on the brakes, this is most likely caused by the sensors on your current pads rubbing and emitting the noise to notify you it is time to have your brake pads replaced.

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SHOCKS AND STRUTS

STRUTS AND SHOCKS
Struts and shocks are used for ride control in the suspension system of a vehicle. They are designed to dampen the movement of the vehicle suspension as it reacts to changes in road surface. Shock absorbers are used with conventional coil spring, leaf spring or torsion bar suspension systems. Shocks serve to control the rebound action of the springs or torsion bars. Shock absorbers contain a large piston rod, hydraulic oil and a control valve. When the shock absorber compresses, the piston rod tries to force the hydraulic oil through an orifice in the control valve. The diameter of the orifice controls the stiffness of the shock absorber. A larger diameter orifice would provide a softer ride feel. Oil is drawn back into the piston area as the shock rebounds.
Gas charged shocks use nitrogen gas in a chamber above the hydraulic oil in the shock absorber. The action of the gas being compressed provides a more responsive shock absorber and a smoother ride. Macpherson struts are very similar to shock absorbers. In fact, they are basically large shock absorbers. The only difference is the Macpherson strut assembly also provides an anchor for the upper half of the vehicle suspension. Failure of shock absorbers can result in excessive tire bounce, excessive chassis bounce, uneven tire wear and wheel vibration or shimmy. Faulty shock absorbers can be revealed by a visual inspection for leaking fluid and worn bushings. A bounce test can be used to diagnose internal shock absorber failure. The bounce test is performed by rapidly pressing down the front or rear bumper of the vehicle and counting the number of times the vehicle bounces after it is released. The vehicle should not bounce more than three times after being released. Excessive bouncing would indicate internal leaking of the shock absorber. Macpherson strut diagnosis is similar to shock absorber diagnosis.

COIL AND LEAF SPRINGS
Both coil and leaf springs are used to provide support for the weight of the vehicle on the axles or suspension components. Coil springs are placed between the frame and the lower control arm. Leaf springs are mounted on the frame at each end and support the axle shaft in the center of the spring. A coil spring is constructed of a long metal rod rolled into a coil. The coil design provides excellent suspension travel when used in conjunction with a shock absorber for spring rebound control. The shock absorber is used to dampen the oscillations of the coil spring as it responds to variations in road surfaces. Leaf springs consist of a series of flat metal bars called leaves stacked upon each other. The longest section of the leaf spring attaches to the frame at each end. Leaves are stacked below the anchoring leaf and each lower leaf is correspondingly shorter than the next. A shock absorber is also used in conjuction with the leaf spring to dampen the oscillations of various road surfaces.

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RACK AND PINION STEERING

The steering gear transfers the rotary motion of the steering wheel to a linear motion used to steer the front wheels. Two types of steering gear are in use today, the standard gear box and the rack and pinion. The standard gear box uses a worm gear that is rotated by the steering wheel to move the pitman shaft. The worm gear contains spiral cut grooves that mesh with a sector gear at the top of the pitman shaft. The spiral action of the worm gear causes the pitman shaft to move the steering linkage in a linear motion. Power steering is achieved by using hydraulic pressure to assist in the rotation of the worm gear.

Rack and pinion steering provides a much simpler method of converting the circular motion of the steering wheel to linear motion for steering. The steering column attaches to the top of the rack and pinion unit and rotates the pinion gear. The pinion gear actuates the rack, which is a simple straight shaft with teeth cut in the top. The rack will simply move back and forth, in a linear motion, in response to the pinion gear. The only steering linkage used is tie rods to indirectly link the rack gear to the steering knuckle. Vehicles with power rack and pinion steering use hydraulic pressure to assist in rotating the pinion gear.

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EMERGENCY BRAKE

The emergency or parking brake is used as a mechanical means to apply the rear brakes for parking or in the event of failure of the brake hydraulic system. Application of the emergency brake is accomplished through a hand or foot operated lever. The operating lever contains a ratchet assembly that allows the brake to be locked in place. A brake warning light switch is connected to the parking brake lever assembly and is used to illuminate the brake lamp when the emergency brake is applied. Diagnosing problems involving the parking brake are fairly straightforward. Refer to your auto repair book for the design details pertaining to your particular vehicle's parking brake configuration, though most designs are very similar if not identical.

The emergency brake is applied by a cable attached to the emergency brake lever. The cable is used to actuate parking brake components located in the rear brake system. Typical drum brake designs use a lever to move the brake linings against the brake drum surface, to apply the parking brake. When the emergency brake cable is moved to the apply position, the lever will force the brake shoe that it is attached to, into the surface of the brake drum. At the same time, the lever will also force the opposite shoe into the brake drum by means of a link placed between the brake shoe and the lever.

Rear disc brake systems typically use one of two different systems as an emergency brake. The most common design uses a lever to actuate an internal screw assembly, at the rear caliper. The screw assembly rotates to apply pressure to the caliper piston, which in turn clamps the brake pads against the brake rotor. A second design incorporates an internal brake drum on the inside of the rear disc brake rotor. Shoes are attached to a small backing plate and are actuated by cable only. When the emergency brake is applied, the shoes are forced against the braking surface on the inside the brake rotor, causing the automobile to slow or even stop. I cannot stress how important it is to make sure the emergency brake is operating flawlessly; it can save your life. If any problems, take your vehicle to an auto repair shop or dealership and have it inspected.

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THE MASTER CYLINDER

All passenger cars and light trucks in the United States today are equipped with a dual master cylinder. The dual master cylinder, also known as a tandem master cylinder, is essentially two separate master cylinders combined into one unit. The dual master cylinder is used as a safety device, to divide the brake hydraulic system into two individual hydraulic circuits. There are two types of split hydraulic systems used. Most rear wheel drive vehicles use a conventional split system, dividing the brake circuits by axle. One half of the master cylinder is used to operate the front brakes, while the other is used to operate the rear brakes. A large number of front wheel drive vehicles use a split diagonal system. The split diagonal system divides the brake circuits between one front wheel and one rear wheel on opposite sides of the vehicle. In the event of pressure loss in one circuit, the other hydraulic circuit would remain operational. The dual master cylinder has been required equipment by law, since 1967. Some automobiles manufactured before 1967 were required to be retrofitted by a certified auto repair mechanic for a dual master cylinder.

The master cylinder is generally constructed of aluminum or cast iron. Attached to or contained in the master cylinder body itself, are two separate brake fluid reservoirs. Master cylinders used with disc/drum combination brake systems will use a large reservoir for the disc brake portion of the system and a small reservoir for the drum brake portion. This is to allow for fluid level changes as the disc pads wear. Inside the master cylinder is a machined bore that contains the master cylinder primary and secondary pistons. Both pistons are combined into a single, two part unit. The section that is closest to the brake push rod is the primary piston, while the section closest to the front of the master cylinder is the secondary piston. Cup seals are placed on the primary and secondary pistons to provide a tight seal in the automobile master cylinder bore. Calibrated springs are placed between the primary and secondary piston and the secondary piston and the end of the master cylinder bore. The area in front of each piston is the pressure chamber area and this is where pressure is created to operate the brake system. There are two ports machined into the master cylinder bore for each brake fluid reservoir. One port is the by-pass port, the other is a compensating port. The by-pass port supplies fluid to the master cylinder bore when the brakes are not applied. The compensating port is used to allow the master cylinder piston to quickly return to the unapplied position, as well as compensate for fluid expansion or contraction from changes in temperature.

The master cylinder is operated by a push rod attached to the brake pedal. When the driver depresses the brake pedal to stop the vehicle, the brake pushrod moves the master cylinder primary piston forward in the master cylinder bore. The secondary piston moves at the same time, operated by hydraulic pressure created in front of the primary piston and the calibrated spring placed between the pistons. As the piston moves forward, the by-pass port is blocked by the cup seal, creating a sealed pressure area in front of the piston. Hydraulic pressure is created by the pressure of the piston on the brake fluid. When the brake pedal is released, it is possible for a vacuum to be created behind the piston as it returns to rest position. To prevent this, the compensating port allows fluid to flow into the area behind the brake piston.

In the event of the loss of one hydraulic circuit, the remaining circuit would be operated in part by the failed circuit piston and the brake pushrod. If the primary circuit were to fail, the loss of pressure would cause the primary piston to move forward in the master cylinder bore, until it bottomed against the calibrated spring and the secondary piston. The primary piston would then act as a connector between the brake pushrod and the secondary piston. If the secondary circuit failed, the secondary piston would move forward against the secondary piston spring, until it reached the end of the master cylinder bore. When the secondary piston reaches the limit of its travel, the primary piston is then able to build pressure in the primary brake circuit. Of course, when diagnosing and troubleshooting the automobile master cylinder and overall braking system, both hydraulic circuits must be tested by an auto repair mechanic for 100% functionality.

Most master cylinder malfunctions are the result of failed seals, as any auto repair mechanic will attest to. Leaks can develop at the rear seal of the master cylinder, resulting in fluid loss at the pushrod area. Cup piston seals can harden or wear, causing brake fluid to leak past the brake pistons, resulting in loss of pressure inside the master cylinder. Poor internal sealing due to worn or hardened cup seals is most evident by the brake pedal slowly sinking to the floor during periods of light brake applications, such as sitting at a stop. If you are not a do-it-yourselfer, make sure you have an auto repair shop inspect your master cylider at least once per year. Generally, the best auto repair facility to have repairs performed is the dealer, although the dealer is usually the most expensive. Independent auto repair shops can be just as reliable, however. Check with your local Chamber Of Commerce or Better Business Bureau to find a reputable auto repair facility.

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JOINTS AND BOOTS

The efficient operating range of a universal joint is about 1-4. When this range is exceeded, the universal joint will start to vibrate excessively. This is caused by the universal joint speeding up and slowing down as it rotates. It is a normal operating characteristic of a universal joint, and is minimized by using the front universal joint to cancel out the rear universal joint. However, this will only work if the universal joint operating angle does not exceed 5 degrees. As the angle increases, the speed fluctuation of the universal joint, as it rotates, rises beyond acceptable limits. Because of this, universal joints are not used on front wheel drive axles. Considering front wheel drive vehicles use the drive wheels to steer the vehicle, the axle shaft must be able to transfer torque at a constant speed, over a wide range of angles. In addition, the axle shaft must be able extend and retract, as the suspension reacts to the road surface. CV joints are installed on the drive axle to provide torque to the drive wheels, at a constant rotational speed, as well as allow the axle to change lengths, with the movement of the suspension.

The axle shaft generally uses two CV joints. The CV joint that is placed on the wheel side of the axle shaft is referred to as the outboard CV joint. The CV joint placed on the transmission side of the axle shaft is referred to as the inboard CV joint. The outboard CV joint is designed to swivel as the wheel is turned while steering. The inboard CV joint is designed to extend or retract as the vehicle suspension moves. For this reason, the inboard CV joint is sometimes referred to as the plunge joint.

Almost all outboard CV joints are the Rzeppa type CV joint. The Rzeppa joint uses a ball and cage design. The CV joint consists of an inner race, slid over splines on the axle shaft, and six balls, placed in individual channels cut in the inner race. A cage is placed over the balls to retain them in the inner race. The assembly is slid into an outer race containing six channels cut to receive the balls. The outer race is part of the axle stub shaft, that protrudes through the front wheel hub. When assembled, the outer race is able to swivel on the ball and inner race assembly. A flexible boot is placed over axle shaft and outer race, covering and sealing the entire CV joint assembly. Special grease is contained in the boot, to lubricate the CV joint.

When the axle shaft is rotating, the inner race transfers torque through the balls, to the outer race. The inner race and balls become the drive member, while the outer race becomes the driven member. When the angle of the CV joint changes, as in when the vehicle is turning, the balls are able to slide laterally in the channels cut in the inner and outer races. This allows the CV joint to use the balls compensate for the difference in angles between the axle shaft and the stub shaft. This allows the CV joint to rotate at a constant speed at angles up to 40 degrees. The most common inboard CV joint is the Tripot type. The Tripot joint consists of three convex rollers, each mounted on three separate shafts. The three shafts are equally spaced apart, in triangular fashion, around ring containing inner splines. The shaft and ring assembly is sometimes referred to as a spider. The spider is slid over the splines of the axle shaft, and held in place by a snap ring. The rollers are placed on the shafts of the spider, with needle bearings placed between the inner surface of the rollers and the outside of the shafts. The spider and roller assembly is placed inside a housing, that is part of the stub shaft, The housing has elongated channels cut into it to receive the convex rollers. A flexible boot is placed around the housing and the axle shaft, covering and sealing the joint. Special lubricant is contained inside the boot.

Torque is transferred from the stub shaft housing, to the roller and spider assembly, using the roller channels. The joint is capable of operating at an angle, but does not have the angular range of the Rzeppa joint. However, like the Rzeppa joint, it is able to operate at a constant rotational speed. The Tripot joint is able to extend or retract, in response to the movement of the vehicle suspension, by the rollers moving in and out of the channels cut in the housing. Some axle shafts use a plunging Rzeppa joint in place of a Tripot joint. The plunging Rzeppa joint is similar to the normal Rzeppas joint, with the exception of longer channels cut into the outer race. This allows the CV joint to compress or extend as the suspension height changes.

The most common cause of CV joint failure is due to lubricant contamination from dirt and/or moisture. This occurs when the CV boots are ripped, cracked, or damaged. When a damaged CV boot is replaced, the CV joint needs to be throroughly cleaned, inspected, and lubricated, prior to reassembly. Outboard CV joint noise complaints, particularly a knocking noise when turning, is generally a result of wear in the internal comoponents of the CV joint. Generally the easiest and most economical repair is replacement of the entire drive axle, with a reconditioned unit.

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EMERGENCY BRAKE OR PARKING BRAKE WON'T HOLD

SYMPTOM SUMMARY
The emergency brake or parking brake will not hold.

USUAL CAUSE The usual cause of this symptom is improper rear brake adjustment. Many vehicles utilize a self adjusting rear brake system. This system maintains adequate brake tension on the rear brakes so that when the parking brake is engaged, the rear brakes hold the vehicle in place.

DIAGNOSIS
The self adjusters re-tension the rear brakes each time the parking brake is engaged or the vehicle is driven in reverse and the brakes are applied. This system needs to be used frequently to maintain the proper rear brake tension. Often, the parking brake is used infrequently, especially on vehicles equipped with an automatic transmission. Due to this, the rear brakes wear and will result in excessive distance between the rear friction material and the rotor or drum. When the parking brake is applied, this excessive distance prevents the friction material from completely and tightly contacting the rotor or drum. This will prevent the parking brake from holding the vehicle.

CORRECTIVE ACTION
You should apply and release the parking brake several times to activate the self adjusters. This may take as many as 10 to 15 times to bring the rear brakes into adjustment. If this is not effective, apply the brakes abruptly while traveling in reverse at low speed. If the parking brake still will not hold, the rear brakes will have to be inspected and adjusted manually. Once the brakes are in proper adjustment, you should utilize the parking brake on a frequent basis to ensure they remain properly adjusted.

PRECAUTIONS, TIPS, and NOTES Brake rotors and drums become extremely hot after vehicle operation and braking. Use caution when working on the braking system.

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I HEAR A LOUD SQUEAL WHEN A/C IS TURNED ON

SYMPTOM SUMMARY
A loud squeal is produced when the A/C is turned on.

USUAL CAUSE
This symptom is usually caused by a loose or worn air conditioning compressor belt. When the A/C is activated the compressor is engaged. This places a load on the engine and the drive belt that rotates the compressor. If the belt is loose or worn the belt can slip on the compressor pulley and emit a loud squeal.

DIAGNOSIS
The drive belts should be inspected for proper tension and wear. A properly tensioned belt should have aproximately 1/2" of deflection at its greatest span between pulleys. Inspect the belt for wear. Belts can become glazed on the inside drive surface which can cause them to slip, which produces the loud squeal. Some vehicles use an automatic tensioner that contains a large spring that keeps constant pressure on the belt. This system automatically tensions the belt to the proper tension. This system is often used on vehices that use a serpentine belt. This type of system uses one belt to drive many accessories.

PRECAUTIONS, TIPS, and NOTES
Use caution when working around hot or rotating engine parts.

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CAR PULLS TO ONE SIDE WHILE DRIVING

SYMPTOM SUMMARY
The vehicle pulls to the right or left. The problem may be worse at higher speeds. If the symptom only occurs during braking, refer to the "Vehicle Pulls When Brakes Are Applied" symptom.

USUAL CAUSE This symptom usually indicates that a front end alignment is needed. It can also be caused by a tire pull or improperly inflated tires.

DIAGNOSIS
Tire pressure and condition should be checked and corrected as necessary. The tires should be rotated from front to rear and the vehicle should be road tested. If the symptom still persists, the front end alignment will have to be inspected and adjusted as necessary.

PRECAUTIONS, TIPS, and NOTES When rotating tires, use the manufacturer's jacking procedures to prevent damage to the vehicle and/or injury to yourself. Use caution when working around a jacked vehicle. Always use jack stands and never rely on the jack as a single method to support the vehicle during servicing.

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BRAKE WARNING LIGHT

The brake warning light is located in the instrument cluster area and is illuminated to warn of brake pressure loss or to indicate application of the parking brake. The brake warning light is supplied voltage from an ignition feed circuit and ground is furnished through two separate switches to illuminate the light. One switch is located in the brake combination valve or the master cylinder. In the event of a failure of one of the hydraulic circuits of the brake system, the switch will close and the light will be illuminated. The other switch is used to warn of parking brake application and is located near the parking brake lever. When the parking brake is applied, the switch is closed and illuminates the brake warning light. This circuit will usually have lower resistance than the pressure warning circuit and cause the warning light to glow brighter during parking brake application. This is done to help differentiate between causes of warning light illumination. When the brake warning light illuminates it does not necessarily indicate that you are facing a large auto repair job. But, when this light goes on, you should seek professional advice as soon as possible by visiting a reputible auto repair shop so they can troubleshoot the problem. Issues involving automobile brakes are not to be taken lightly; the ability to stop your vehicle is a very serious matter (of course).

The brake warning light (not to be confused with the ABS or anti-lock warning light) will light up when one of the following occurs:

1) Parking brake cable doesn't completely release (or the parking brake mechanism doesn't fully disengage)

2) Loss of brake fluid

3) Hydraulic pressure imbalance in the master cylinder

Does the light come on only in cold weather? There may be moisture buildup in the brake fluid and this moisture is actually freezing when the outside temperature falls below 32F for extended periods of time. Such freezing will cause an imbalance in the brake fluid pressure. If your car is more than five years old, has the brake fluid been flushed? If no, then the glycol-based hydraulic fluid probably has absorbed a some moisture from the atmosphere, and this moisture is freezing in cold weather.

If such moisture is indeed freezing, it may be preventing the brake system from developing equal hydraulic pressure in both halves of the master cylinder, thus creating a pressure imbalance; this will trigger the brake warning light. Get the brake system flushed and bled at your nearest auto repair shop. This will flush out all moisture in the brake system. Further, it will eliminate further corrosion of brake parts like: brake lines, calipers, master cylinders, and ABS units. If you can afford it, have your brake fluid flushed by a reputible auto repair shop every 12,000 miles.

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Brake System Overview

Early automobile brake systems consisted of cable operated brake lining, usually mounted on one axle. The system provided extremely poor stopping power and did not always apply brake pressure evenly to the wheels. This could cause one wheel to lock up and make the vehicle difficult to control during stops. Front brakes were rarely equipped on early vehicles. The need to have the front wheels move from side to side for steering made installation of a cable operated brake system an engineering nightmare. The invention of hydraulic brake systems provided safe, high powered and even braking for automobiles and light trucks. Hydraulic brake systems have been in use for several decades. While the last thirty-five years has seen a number of changes made to the brake system, the basic principle of operation has remained the same since the use of hydraulic brakes began. There are some auto repair garages which specialize in automotive braking andsuspension, but any auto repair shop should be able to inspect and make the necessary brake repairs.

What makes hydraulic brakes possible is the fact that a liquid cannot be compressed. This is the primary operating principle of all hydraulic systems. Hydraulic theory states that when pressure is placed on a liquid in an enclosed system, that liquid exerts the same pressure, equally in all directions inside that container. This is what allows a master cylinder to apply even brake pressure to all four wheels of a vehicle. If a master cylinder generates 1000 psi of pressure to the left front wheel, it also is transmitting 1000 psi to every other component in the brake system.

While hydraulics provide the operating force for the brake system, it is friction that causes a vehicle to stop. The energy that is created by a moving vehicle is converted to heat during stopping, by the friction of the brake linings against the brake rotor or drum surface. The heat generated is then dissipated through the rotors or drums to the outside air. It is the ability of these brake components to dissipate heat, that makes safe stopping possible. Heat buildup in the brake linings and drums or rotors during repeated heavy braking, can cause loss of braking power or brake fade. The ability to rapidly disperse heat is one of the characteristics that make disc brake systems so desirable. No automotive system is as important as your brakes. Therefore, you should inspect or have an auto repair mechanic inspect your braking system regularly. Make sure the repair shop flushes your brake fluid at least every 24,000 miles.

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THE BRAKE SYSTEM

BRAKE SHOES
Vehicles equipped with a drum brake system use brake shoes to stop the vehicle, by creating friction between the brake lining and the inside surface of the brake drum. The brake shoes consist of heat resistant friction material, bonded or riveted to a metal shoe. Hydraulic pressure is applied to the wheel cylinder which forces the brake shoe into the brake drum. Diagnosing and troubleshooting automotive brakes and doing the necessary repairs is a very doable task as brakes are not difficult to understand and most of the components are easily accessible.

There are two basic types of drum brake lining arrangements used on vehicles. Servo and dual servo brake systems. Dual servo brakes are a self energizing type of drum brake system, mostly used on older domestic vehicles. The brake shoe arrangement uses a primary shoe and a secondary shoe connected at the bottom, using the automatic brake adjuster screw. The primary shoe uses a smaller amount of lining than the secondary shoe and the material is usually softer. When the brakes are applied, the rotation of the brake drum causes the top of the primary shoe to be pulled forward in the same direction as the brake drum. This causes the primary shoe to apply pressure to the secondary shoe, through the brake adjuster screw. This action is called self energizing since it creates its own force to assist the brake hydraulic system in applying the brakes. Single servo brakes simply use the wheel cylinder alone to force the brake shoes against the drum surface. Both the leading and trailing shoe are usually the same size and manufactured out of the same material.

The brake shoes are mounted on a plate that is bolted to the rear axle housing, on rear wheel drive vehicles or to the rear spindles, on front wheel drive vehicles. The mounting plate is referred to as the backing plate. Older model vehicles with four wheel drum brakes will use a backing plate attached to the front spindles, as well. The brake shoes are attached to the backing plate using spring loaded retaining pins. The spring loaded retaining pins are used to allow lateral movement of the brake shoes for brake application. Refer to an appropriate auto repair manual to see diagrams for your particular vehicle.

The brake shoes are held in a retracted position by the brake return springs. There are many different configurations of brake return spring arrangements, depending upon the systems design. The brake return springs can be anchored at a central point at the top of the backing plate and attached to the brake shoes. Some vehicle drum brake systems use a single spring to connect the leading brake shoe to the trailing brake shoe. Some systems use a large rigid metal bar as a brake return spring. The bar is bent into a U shape, with the upper ends of the U attaching to the top of the leading and trailing shoe. The brake linings are retained in a closed position by the tension of the metal bar. Contained in the drum brake system hardware, are provisions for automatic adjustment of the clearance between the brake linings and the brake drum. Automatic brake adjuster designs vary widely rom vehicle to vehicle. Most older domestic vehicles use an automatic brake adjustment system that operates when the brakes are applied while in reverse. Most recent designs use an automatic brake adjuster system that operates when the parking brake is applied.

BRAKE DRUMS
Brake drums are used as a friction surface for the brake linings. They are designed to dissipate the heat created by friction to the outside air. Some designs contain external ribs for improved heat transfer. Brake drums are usually constructed of steel or aluminum. The internal friction surface is machined to a smooth surface. Thickness of the friction surface of the brake drum helps to determine the ability of the brake drum to dissipate heat. For this reason, brake drums should never be machined beyond their specified diameter; check the manufacturer's auto repair book for the machining spec.

WHEEL CYLINDERS
Wheel cylinders are used to apply force to the brake shoes using hydraulic pressure. They are normally mounted at the top of the backing plate, where they are connected to the brake shoes, either directly or using link pins. Typical designs consist of a single bore cylinder containing two pistons that move in opposite directions when the brakes are applied. The pistons are sealed in the wheel cylinder bore using cup seals. The cup seals are placed on the inboard side of the wheel cylinder piston, with the cup portions of the seals for the opposite pistons facing one another. A spring with conical washers attached at either end, is placed between the wheel cylinder cups. The conical washer is used as a cup expander, to provide a tighter seal for the wheel cylinder cup against the wheel cylinder bore. Not all designs will use a cup expander on the wheel cylinder spring. Some designs of master cylinders use a residual pressure check valve to maintain a slight amount of hydraulic pressure on the rear brake circuit, to prevent wheel cylinder cup leakage.

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BRAKE ROTOR AND CALIPER

One of the more doable jobs in auto repair is that which involves the brakes. The brake rotor provides a friction surface for the brake pads. It is designed to dissipate the heat generated by friction during braking. The ability of a brake rotor to properly disperse heat relates to the size of the brake rotor. The measurement of the thickness of the brake rotor is designed to provide the greatest heat dissipation possible. Machining the brake rotor below those specifications can cause excessive heat build-up during heavy braking. The brake rotor may have cooling fins set in the center to provide ventilation for improved heat dissipation. The surface of the brake rotor is machined to a smooth finish to provide better brake pad to rotor contact and to ensure more even braking. The brake rotor can be easily damaged by metal to metal contact from worn out brake pads. Scoring of the brake rotor surface below minimum thickness levels can quickly occur if the brake pads were worn down to the metal backing plate. Brake rotors can become distorted by improper tightening of the wheel mounting bolts. This can result in warped brake rotors and a pulsating brake pedal. For this reason, wheel mounting bolts should always be tightened to proper torque specifications. When diagnosing and troubleshooting a shaking front end while braking, always consider the possibility of warped brake rotors before engaging in an auto repair brake job.

There are three types of disc brake calipers used in passenger cars and light trucks: fixed, sliding, and floating. The fixed caliper is the oldest design of brake caliper in use. They first started appearing on import and domestic performance vehicles in the 1960's. Most vehicles today use the single piston sliding or floating caliper. Sliding and floating calipers are cheaper to manufacture and more simple in design than the fixed caliper. Basic disc brake caliper operation is accomplished by using hydraulic pressure to actuate the disc brake caliper piston. The caliper can contain up to four pistons, depending on the type used. Each piston is mounted in a bore machined into the caliper. A round, square cut, "O" ring seal is contained in a groove cut into the caliper bore and provides a seal for the caliper piston. A dust seal is placed around the lip of the caliper piston at the brake pad contact area and is secured in a groove on the outside of the caliper bore. A hydraulic seal is maintained through contact of the caliper piston surface with the caliper seal. The caliper seal also provides two other functions in the disc brake caliper. It acts as a brake return spring to maintain correct clearance between the brake pad and the rotor. The caliper seal is able to do this because of its placement in the groove cut in the caliper bore. The seal groove is cut slightly wider than the caliper seal. When the automotive brakes are applied, the piston slides forward in the bore, moving the caliper seal against the edge of the seal groove. This causes the seal to distort in the same direction as the movement of the piston. When the brakes are released, pressure is removed from the piston and the distortion of the caliper piston seal causes it to pull the piston back slightly and create a small amount of clearance between the brake pads and the rotor. This same design allows the piston to move slightly outward as the brake pads wear, when the brakes are applied, due to contact between the seal and the piston surface. When doing an auto repair job involving the brakes, make sure you take note of this very critical design feature.

The fixed disc brake caliper uses pistons mounted in the caliper on both sides of the rotor. Hydraulic brake fluid is supplied to both pistons through passages bored inside the caliper. Pressure is applied directly to both brake pads by the reaction of the pistons to hydraulic pressure from the master cylinder. The sliding and floating disc brake calipers generally use one large piston for disc brake pad application. The piston is located on the inboard side of the caliper and directly applies pressure to the inboard brake pad. When the brakes are applied, hydraulic pressure forces the brake piston outward against the inboard pad. That same hydraulic pressure, also forces the caliper assembly in the opposite direction and because the caliper is allowed to float on pins or slide in the mounting bracket, the caliper will provide a clamping action for the outboard brake pad at the same time. This design will use a large piston to multiply the hydraulic force of the automotive master cylinder.

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