Component Tests

Inspection and Verification

Brake Pads

NOTE: It is not required to install new brake pads if friction material properties are within guidelines. It is also not required to install new brake pads 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 2 mm (0.079 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 mm (0.07 inch).
- Install new brake pads if there are missing chunks or cracks in the lining through to the backing plate.
- If the friction material thickness varies by more than 3 mm (0.11 inch) in any direction (taper wear), verify the caliper guide pins are functioning correctly.

Brake Discs

CAUTION: Using an impact tool without a torque socket will lead to unevenly tightened lug nuts. This causes brake disc on-vehicle lateral runout and brake roughness.

NOTE: It is generally not required to install new brake discs to address noise issues.

^ Remove the brake disc.
^ 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 discs 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 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, then carry out these 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 foreign material 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 grease to lubricate the bores and guide pins.

Brake Hoses 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 the 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.
^ The wet appearance on the outer cover of rubber brake hoses is called "sweating". This is a normal condition for neoprene rayon braid hose and is not a sign of leakage or cause to install a new hose.

Install a new 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

NOTE: The wet appearance on the outer cover of rubber brake hoses is called "sweating". This is a normal condition for neoprene rayon braid hose. The sweating condition is not evidence of a brake fluid leak and will not result in a loss of pressure in the system.

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 these 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
These 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 will fall during brake application and rise during release. The net fluid level (such as after brake application and release) will remain unchanged.

Condition 2: A trace of brake fluid will exist 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 will decrease 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. Symptom Chart

Brake Booster
Inspect the brake booster for:
^ 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 Chart

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.

Brake System Leak Check

1. NOTE: Brake fluid is water soluble and therefore evidence of leakage can be washed away if the vehicle is operated in rain or snow.

Fill the brake master cylinder reservoir.
2. Apply and hold the brakes several times.
3. Check the brake master cylinder reservoir to verify fluid loss.
4. Inspect the brake system for signs of fresh brake fluid leakage.
5. Locate and correct the source of the external leak.