Inspection and Verification
Inspection and VerificationWARNING: Use of any brake fluid other than the approved DOT 3 will cause permanent damage to brake components and will render the brakes inoperative. Failure to follow these instructions may result in personal injury.
WARNING: Brake fluid contains polyglycol ethers and polyglycols. Avoid contact with eyes. Wash hands thoroughly after handling. If brake fluid contacts eyes, flush eyes with running water for 15 minutes. Get medical attention if irritation persists. If taken internally, drink water and induce vomiting. Get medical attention immediately. Failure to follow these instructions may result in personal injury.
CAUTION: Brake fluid is harmful to painted and plastic surfaces. If brake fluid is spilled onto a painted or plastic surface, immediately wash it with water.
NOTE: The ignition key must be in the ON position when checking the brake fluid level.
NOTE: Always check the fluid level in the brake master cylinder reservoir before carrying out the test procedures. If the fluid level is not at the correct level, clean the reservoir cap before removing, then add DOT 3 brake fluid.
NOTE: Prior to carrying out any diagnosis, make sure the brake warning indicator operates correctly.
The first indication that something may be wrong in the brake system is a change in the feeling through the brake pedal. The brake warning indicator in the instrument cluster and the brake fluid level in the brake master cylinder reservoir are also indicators of system concerns.
If a wheel is locked and the vehicle must be moved, open a bleeder screw at the locked wheel to let out enough fluid to relieve the pressure. Close the bleeder screw. This bleeding operation may release the brakes but will not correct the cause of the concern. If this does not relieve the locked wheel condition, repair the locked components before proceeding.
Inspect all hoses and connections. All unused vacuum connectors should be capped. Make sure hoses and their connections are correctly secured and in good condition with no holes, soft or collapsed areas.
Road Test
The technician should have a thorough knowledge of the brake system operation and accepted general braking guidelines in order to detect any problems.
Select a road that is reasonably smooth and level. Gravel or bumpy roads are not suitable because the surface does not allow the tires to grip the road equally. Avoid crowned roads.
A key factor in evaluating brake concerns is the deceleration rate. This varies from vehicle to vehicle and with changes in operating conditions. It is evident how well the brakes are working after Just a few applications.
For low or spongy brake pedal concerns:
^ check and, if necessary, refill the brake master cylinder reservoir.
^ bleed the brake system and retest the brake pedal feel.
^ if the brake pedal is still low or feels spongy, check the brake pedal mounting for looseness and correct installation. Check the brake booster and the brake master cylinder for loose mounting. Correct as necessary and retest the system for normal operation.
For a slow or incomplete brake pedal return concern:
^ inspect for binding, damage, correct installation or interference at the brake pedal.
^ check the brake booster for binding, damage and correct installation.
Brake Pads
NOTE: New brake pads are not required if the friction material properties are within the guidelines. New brake pads are not required when the brake discs are machined.
^ Remove the brake pads.
^ Inspect and measure the thickness of the brake pad friction material.
- Install new brake pads if the thickness of the friction material is less than 3 mm (0.118 inch).
- Compare all four front or rear pads for uneven wear. Install new brake pads if the thickness of the friction material varies from pad to pad by more than 2 mm (0.079 inch).
- Install new brake pads if there are missing pieces or cracks in the lining through the backing plate.
- If the friction material shows taper wear (for example: the thickness varies by more than 3 mm (0.118 inch) any direction), or if the pads show uneven wear (2 mm (0.079 inch) difference between the inboard and the outboard pad), verify the caliper guide pins are functioning correctly.
Brake Discs
CAUTION: Using an impact tool without a torque socket will lead to unevenly torqued lug nuts. This causes brake disc on-vehicle lateral runout and brake roughness.
NOTE: It is generally not necessary to install new brake discs to address noise issues.
^ Remove the brake discs.
^ Inspect the brake discs and measure the brake disc thickness in a minimum of 4 places around the circumference of the brake disc. Record the measurements.
- Install new brake discs if any thickness measurement is less than the minimum specification.
- Install new brake disc if cracked.
- Machine the brake discs if the diagnosis has revealed vibration in the steering wheel, seat, or pedal while braking. Heavily scored brake discs, similar to that caused by pads worn down to the backing plate, should also be machined. In order to machine, discs must be above the minimum thickness to machine specification.
Brake Caliper
Inspect the brake calipers for the following:
^ brake fluid leaks.
^ boots and seals for tears or cracks.
^ caliper piston for binding and corrosion.
^ guide pins for correct operation.
Brake Caliper Guide Pins
CAUTION: Do not use power tools for caliper guide pin bore cleaning.
The guide pins should slide with a reasonable amount of hand force. If the brake pads show taper wear or if the guide pins are difficult to move, then carry out the following steps.
NOTE: If a guide pin kit is not available, install a new caliper assembly.
Disassemble the guide pins.
^ Use a wire brush, rolled-up sandpaper, or emery cloth to remove all corrosion and foreign material from the caliper guide pin bores. Clean any remaining debris from the bores with brake parts cleaner and compressed air.
^ Install new brake pads if the lining is not within specifications.
^ Assemble the caliper guide pins using new caliper seals, boots, and guide pins. Use an ample amount of silicone grease to lubricate the bores and guide pins.
Brake Drums
CAUTION: Manual adjustment of the rear brake drum assemblies should only be done when the rear brake shoes are replaced, new drums are installed, or existing drums are machined. If the rear brake drum assembly is not adjusted correctly, brake drag, grab, lock, overheating, and fade may occur.
^ Remove the brake drum.
^ Inspect the brake drum and measure the brake drum inside diameter in a minimum of 4 places around the circumference of the brake drum. Record the measurements.
- Install a new brake drum if any diameter measurement is greater than the maximum specification.
- Install a new brake drum if cracked.
- Heavily scored brake drums, similar to that caused by shoes worn down to the backing plate, should be machined. In order to machine, drums must be below the maximum diameter specification.
Brake Shoes
^ Inspect and measure the thickness of the brake shoe friction material.
- Install new brake shoes if the thickness of the friction material is less than the minimum specification.
- Install new brake shoes if there are cracks in the lining through to the backing plate or if there are chunks missing.
- Verify that the mounting hardware is installed correctly and operating correctly.
- Verify that the backing plate contact points are free of corrosion that may cause binding.
Brake Lines and Tubes
CAUTION: Never use copper tubing. It is subject to fatigue, cracking, and corrosion, which could result in brake tube failure.
^ Double-wall steel tubing is used throughout the brake hydraulic system. All brake tube fittings must be correctly double-flared to provide strong, leakproof connections. When bending tubing to fit underbody or rear axle contours, be careful not to kink or crack the tube.
^ If a section of brake tube is damaged, the entire section must be installed new with a tube of the same type, size, shape, and length.
^ When installing the hydraulic brake tubing, hoses, or connectors, tighten all connections to specification. After installation, bleed the brake system.
^ The wet appearance of the outer cover of rubber brake hoses is called sweating. This is a normal condition for neoprene rayon-braided hose and is not a sign of leakage or cause to install a new hose.
Install a new flexible brake hose if the hose shows signs of softening, cracking or other damage.
When installing a new brake hose, position the hose to avoid contact with other vehicle components.
Non-Pressure Leaks
The only part of the brake system that could have a brake fluid loss that does not appear when the system is under pressure is the brake master cylinder reservoir under the following conditions:
^ missing or poorly-fitted brake master cylinder filler cap
^ punctured or otherwise damaged brake master cylinder reservoir
^ missing or damaged brake master cylinder filler cap gasket
^ missing, damaged, or poorly-fitted sealing grommets between the brake master cylinder and the brake master cylinder reservoir
The brake master cylinder reservoir grommets are not repairable and must be installed new as part of a new brake master cylinder reservoir.
Brake Master Cylinder - Normal Conditions
The following conditions are considered normal and are not indications that the brake master cylinder is in need of service.
Condition 1: During normal operation of the brake master cylinder, the fluid level in the brake master cylinder reservoir rises during brake application and falls during release. The net fluid level (such as after brake application and release) remains unchanged.
Condition 2: A trace of brake fluid exists on the booster shell below the master cylinder mounting flange. This results from the normal lubricating action of the master cylinder bore and seal.
Condition 3: Fluid level decreases with pad wear.
Brake Master Cylinder - Abnormal Conditions
Changes in brake pedal feel or travel are indicators that something could be wrong in the brake system. GO to Symptom Chart for abnormal condition diagnosis. Diagnosis By Symptom
Parking Brake
Check the operation of the parking brake system with the vehicle on a hoist and the parking brake control fully released. Check for any damaged cables and install new components as necessary. Check the rear brake adjustment or carry out the brake system diagnosis.