Component Tests and General Diagnostics

Component Tests

Warning:
^ Use of any other than the approved DOT 3 brake fluid will cause permanent damage to brake components and will render the brakes inoperative. Failure to follow these instructions may result in personal injury.

Note:
^ Always check the brake fluid level in the brake master cylinder reservoir before performing the test procedures.

If the brake fluid level is not at the MAX line on the brake master cylinder reservoir, add DOT 3 brake fluid.

Brake Booster-Operation Check
1. Inspect all vacuum hoses and connections. All unused vacuum connectors must be capped. Hoses and their connections must be correctly secured and in good condition with no holes, cracks, or collapsed areas.
2. Check the brake hydraulic system for leaks or insufficient brake fluid. Repair as necessary.
3. With the engine off, place the transaxle in PARK (A/T) or NEUTRAL (M/T) and apply the parking brake.

Note:
^ If the power brake booster is noisy when the brakes are applied, new one must be installed.

4. Press the brake pedal several times to exhaust all of the vacuum from the system.
5. Press and hold the brake pedal.
6. Start the engine. If the vacuum system is operating, the brake pedal will move downward under constant foot pressure. If no movement occurs, the power brake booster system is not functioning.
7. Remove the vacuum booster hose from the power brake booster.
8. Place the transaxle in PARK (A/T) or NEUTRAL (M/T) and apply the parking brake. Start the engine. Manifold vacuum should be available from the vacuum booster hose. If manifold vacuum is not available, inspect all of the hoses and hose connections. Repair as necessary.
9. Reconnect the vacuum booster hose and run the engine at fast idle for10 seconds.
10. Stop the engine and let the vehicle stand for 10 minutes.
11. Apply the brake pedal with approximately 89 Nm (20 ft. lbs.) of force. The brake pedal feel should be the same as normal power assisted brake operation for at least one application. If the brake pedal feel is normal, then the power brake booster is OK. If the brake pedal feels hard, continue with the test.
12. Remove the vacuum booster hose from the power brake booster. Apply 57.3 kPa (17 in-Hg) of vacuum to the vacuum booster hose. If the vacuum does not leak off after10 minutes, install a new power brake booster. If the vacuum does leak off, install a new check valve and/or new vacuum booster hoses.

Check Valve
13. Remove the vacuum booster hose from the power brake booster.
14. Apply 57.3 kPa (17 in-Hg) of vacuum to the vacuum booster hose. If the vacuum does not leak off after ten minutes, the check valve is OK. Otherwise. install a new check valve.

Brake Master Cylinder-Normal Conditions
The following conditions are considered normal and are not indications that the brake master cylinder is in need of repair or new installation.

Condition 1. During normal operation of the brake master cylinder, the brake fluid level in the brake master cylinder reservoir will fall during brake application and rise during release. The net brake fluid level will remain unchanged after brake application and release.

Condition 2. A trace of brake fluid may exist on the power brake booster shell below the brake master cylinder mounting flange. This is the result of the normal internal lubricating action of the brake master cylinder.

Condition 3. Brake fluid level will decrease as the brake shoes and linings wear.

Brake Master Cylinder-Abnormal Conditions
Changes in brake pedal feel and travel are indications that a brake system concern exists. Refer to SYMPTOM TROUBLESHOOTING CHART for abnormal condition diagnosis. Symptom Index (Symptom Charts)

Brake Master Cylinder-Bypass Condition Test
15. Check the brake hydraulic system for leaks or insufficient brake fluid. Repair as necessary.
16. Observe the brake fluid level in the brake master cylinder reservoir as the brake pedal is slowly pressed and quickly released. If the brake fluid level rises when the brake pedal is pressed and drops when the brake pedal is released, but the net brake fluid level remains unchanged, the brake master cylinder is bypassing. Repair or install a new brake master cylinder.

Brake Master Cylinder - Non-Pressure External Leaks
A low brake fluid level in the brake master cylinder reservoir may be caused by the following non-pressure external leaks:

Type 1. An external leak may exist at the brake master cylinder filler cap due to incorrect position of the cap, cap gasket, or cap gasket deterioration.

Type 2. An external leak may exist at the brake master cylinder mounting flange due to internal seal failure. Repair or install a new brake master cylinder.

Type 3. An external leak may exist at the base of the brake master cylinder reservoir due to reservoir mounting seals. Repair or install a new brake master cylinder.

Brake Master Cylinder-Compensator Port Check
The purpose of the compensator ports in the brake master cylinder is to:
^ Supply additional brake fluid from the brake master cylinder reservoir needed by the brake system due to brake shoe and lining wear.
^ Allow brake fluid to return to the brake master cylinder reservoir when the brakes are released. The ret turning brake fluid will create a slight turbulence in the brake master cylinder reservoir. This is a normal condition and indicates that the compensator ports are not clogged.

Clogged compensator ports may cause the brakes to hang up or not fully release. If clogged compensator ports are suspected, proceed as follows:

17. Raise and support the vehicle.
18. With the brakes released attempt to rotate each wheel. If an excessive amount of brake drag exists, continue with the test. If an excessive amount of brake drag exists at only one wheel, it indicates a possible seized front disc brake caliper. rear wheel cylinder, or parking brake compor1ent. Repair or install new components as necessary.
19. Check the brake pedal position (BPP) switch adjustment, and brake pedal free play to verify that the brake pedal is not partially applied
20. Loosen the nuts attaching the brake master cylinder to the power brake booster and pull the brake master cylinder away from the power brake booster
21. Repeat Steps 1 and 2. If the brake drag disappears, the power brake booster is binding and new one must be installed. If the brake drag continues, the brake master cylinder is binding and new one must be installed.