Service Diagnosis
GENERAL INFORMATIONService diagnosis for the Premier four-wheel disc brake system is similar to the standard system.
The preliminary diagnosis and road test procedures in the Premier Service Manual also apply to four-wheel disc brake models. Only those differences unique to the four-wheel disc brake system are covered in this section.
DIAGNOSING BRAKE PROBLEMS
Pedal Falls Away
A brake pedal that falls away under steady foot pressure is generally the result of a system leak. The leak point could be at a brake line, hose, or caliper if no external leak is evident. Internal leakage in the master cylinder (fluid leaks past worn or damaged piston cups) could also be the problem cause.
If leakage is severe, fluid will be evident at or around the leaking component. However, internal leakage in the master cylinder will not be physically evident.
Low Pedal
If a low pedal is experienced, pump the pedal several times. If the pedal comes back up, worn brake linings or rotors are the most likely causes.
A slightly low master cylinder fluid level may accompany a low pedal condition. It is a result of the normal outward movement of the caliper pistons to compensate for lining wear.
Spongy Pedal
A spongy pedal is most often caused by air in the hydraulic system. However, substandard brake lines and hoses will also contribute to a spongy pedal.
The rear wheels on the Premier model should be at normal ride height for satisfactory rear caliper bleeding. Air could be trapped in the calipers if the wheels are at a full rebound position. Position the vehicle on a drive-on hoist or raise the rear wheels to normal ride height before bleeding.
Hard Pedal/High Pedal Effort
Hard pedal or high pedal effort may be due to lining that is water soaked, contaminated, glazed, or badly worn. The power booster or check valve could also be faulty. Test the booster and valve as described in Group 5 of the Premier Service Manual.
Brake Drag
Some common causes of rear disc brake drag are: loose, damaged hub or wheel bearing, seized or sticking caliper piston, caliper slide pins corroded, misadjusted parking brake cable, or caliper self adjuster malfunction.
If brake drag occurs at all wheels, the problem may be related to a blocked master cylinder return port, faulty power booster (binds, does not release) or contaminated brake fluid. If only the rear wheels are affected, the proportioning valve could also be at fault.
Brake Fade
Brake fade is a result of overheating caused by brake drag. However, brake overheating and subsequent fade can also be caused by riding the brake pedal, making repeated high deceleration stops in a short time span, or constant braking on steep mountain roads. Refer to the Brake Drag information in this section for causes of brake drag.
Pedal Pulsation
Disc brake rotors or mounting hubs with excessive lateral runout or thickness variation are the primary causes of pulsation. Other causes are loose, worn wheel bearings, calipers and damaged axles or tires.
Brake Noise
Squeak/Squeal
Brake squeak or squeal may be due to linings that are wet or contaminated with brake fluid, grease, or oil. Glazed linings or rotors with hard spots can also contribute to squeak. Dirt and foreign material embedded in the brake lining can also cause squeak/squeal.
A very loud squeak or squeal is frequently a sign of severely worn brake lining. If the lining has worn through to the brake pads in spots, metal-tometal contact occurs. If the condition is allowed to continue, rotors can become scored and replacement may be necessary.
Thump/Clunk
Thumping or clunking noises during braking are frequently not caused by brake components. In many cases, such noises are caused by loose or damaged steering, suspension, or engine components. However, calipers that bind on the slide pins can generate a thump or clunk noise.