Initial Inspection and Diagnostic Overview
Inspection and VerificationWARNING: Use of any brake fluid other than the approved DOT 3 will cause permanent damage to brake components and 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: 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 red brake warning indicator is functional. Refer to Instrument Panel, Gauges and Warning Indicators.
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 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, or 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:
^ 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.
^ check the fluid level. The fluid level must be at or above the minimum mark. If the fluid level is below the minimum mark, check the system for leaks.
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 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 3.0 mm (0.118 inch).
- Compare all 4 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 2.0 mm (0.079 inch).
- Install new brake pads if there are missing chunks or cracks in the lining through to the backing plate.
- If the friction material shows taper wear (i.e. the thickness varies by more than 3.0 mm (0.118 inch) in any direction), or if the pads show uneven wear (2.0 mm [0.079 inch] difference between the inboard and the outboard pad), verify the caliper guide pins are functioning correctly.
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 the guide pins are difficult to move, 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 remaining debris from the bores with brake parts cleaner and compressed air.
^ Install new brake pads if the lining is not within specification.
^ Assemble the caliper guide pins using new caliper seals, boots, and guide pins. Use an ample amount of grease to lubricate the bores and guide pins.
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 the 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 specifications. After installation, bleed the brake system. Refer to Brake System Bleeding.
^ The wet appearance on the outer cover of rubber brake hoses is called sweating. This is a normal condition for rayon-braided neoprene 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.
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: The fluid level decreases with pad wear.
Brake Master Cylinder - Abnormal Conditions
Changes in the brake pedal feel or travel are indicators that something could be wrong in the brake system. GO to Symptom Chart for abnormal condition diagnosis.Symptom Related Diagnostic Procedures
Brake Booster
Inspect the brake booster for the following:
^ excessive corrosion or damage
^ vacuum connections for leakage
^ vacuum hoses for kinks or leakage
^ brake booster check valve for correct operation. Changes in the brake pedal feel or travel are indicators that something could be wrong in the brake system. GO to Symptom Chart for abnormal condition diagnosis.Symptom Related Diagnostic Procedures
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.