Brake System Diagnosis

Brakes should be tested on a dry, clean, reasonably smooth, and level roadway. A true test of brake performance cannot be made if roadway is wet, greasy, or covered with loose dirt so that all tires do not grip the road equally. Testing will also be adversely affected if roadway is crowned so as to throw weight of car toward wheels on one side or if roadway is so rough that wheels tend to bounce.

Test brakes at different car speeds with both light and heavy pedal pressure; however, avoid locking the brakes and sliding the tires. Locked brakes and sliding tires do not indicate brake efficiency, since heavily braked but turning wheels will stop car in less distance than locked brakes. More tire-to-road friction is present with a heavily braked turning tire than with a sliding tire.

The standard brake system is designed and balanced to avoid locking the wheels except at very high deceleration levels. It is designed this way because the shortest stopping distance and the best control is achieved without brake lock-up.

Because of high deceleration capability, a firmer pedal may be felt at higher deceleration levels.

EXTERNAL CONDITIONS THAT AFFECT BRAKE PERFORMANCE
1. Tires. Tires having unequal contact and grip on road will cause unequal braking. Tires must be equally inflated, identical in size, and the tread pattern of right and left tires must be approximately equal.
2. Car Loading. When a car has unequal loading, the most heavily loaded wheels require more braking power than others. A heavily loaded car requires more braking effort.
3. Wheel Alignment. Misalignment of the wheels, particularly in regard to excessive camber and caster, will cause the brakes to pull to one side.

BRAKE FLUID LEAKS
With the engine running at idle and the shift lever in neutral, depress the brake pedal and hold constant foot pressure on the pedal. If the pedal gradually falls away with constant pressure, the hydraulic system may be leaking. Perform a visual check to confirm any suspected leaks.

Check the master cylinder fluid levels. While a slight drop in reservoir level does result from normal lining wear, an abnormally low level in either reservoir indicates a leak in the system. The hydraulic system may be leaking either internally or externally.

SUBSTANDARD OR CONTAMINATED BRAKE FLUID
Improper brake fluid, mineral oil, or water in the fluid may cause the brake fluid to boil or the rubber components in the hydraulic system to deteriorate.

If primary piston cups are swollen, then rubber parts have deteriorated. This deterioration may also be evidenced by swollen wheel cylinder piston cups on the drum brake wheels or master cylinder fluid reservoir cover diaphragm.

If deterioration of rubber is evident, disassemble all hydraulic parts and wash with denatured alcohol. Dry these parts with compressed air before assembly to keep alcohol out of the system.

CAUTION: DO NOT USE LUBRICATED COMPRESSED AIR ON BRAKE PARTS AS DAMAGE TO RUBBER COMPONENTS MAY RESULT.

Replace seals or master cylinder assembly as necessary. Replace all rubber parts in the system, including hoses. Also, when working on the brake mechanisms, check for fluid on the linings. If excessive fluid is found, replace the linings.

If the master cylinder piston seals are satisfactory, check for leakage or excessive heat conditions. If condition is not found, drain fluid, flush with brake fluid, refill, and bleed the system.