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How To Fix Common Brake Problems

brake failure

Brake problems usually indicate the need for certain repairs or replacement parts, so here is a quick review of some common fixes:

LOW BRAKE FLUID Usually indicates a leak in the brake system which poses a serious safety hazard. The calipers, wheel cylinders, brake hoses and lines, and master cylinder all need to be inspected. If a leak is found, the defective component must be replaced or rebuilt. The vehicle should not be driven until the repairs can be made because a leak may lead to brake failure.

LOW BRAKE PEDAL Can result if shoe adjusters on drum brakes stick and fail to compensate for normal lining wear. Adjusting them may restore a full pedal, but unless the adjusters are cleaned or replaced the problem will return as the linings wear. Other causes include worn brake linings or a fluid leak.

SPONGY OR SOFT BRAKE PEDAL Means there is air in the brake system either as a result of improper bleeding, fluid loss or a very low fluid level. The cure is to bleed the brakes using the sequence recommended for the specific vehicle. Another possible cause is a rubber brake hose that is "ballooning" when the brakes are applied.

EXCESSIVE BRAKE PEDAL TRAVEL Possible causes include worn brake linings, misadjusted drum brakes, and air in the brake lines. Potentially dangerous because the system may run out of pedal before the vehicle can be safely stopped.

PEDAL SINKS TO FLOOR A dangerous condition caused by a worn master cylinder or a leak in the hydraulic system will not allow the brakes to hold pressure.

check brake rotor thickness with a micrometer

BRAKE PEDAL PULSATION Indicates a warped brake rotor that needs to be resurfaced or replaced. The faces of a rotor must be parallel (within .0005 inch on most cars) and flat (no more than .003 inches of runout as a general rule on most cars and trucks, but some cars cannot tolerate any more than .0015 inches of runout). Excessive runout can be corrected by resurfacing the rotors in place with an on-car brake lathe, or by installed special tapered shims between the rotors and hub to correct the runout. A source for these tapered shims is Brake Align. Do not forget the wheel bearings (if serviceable) -- they all need to be cleaned, inspected and repacked with grease. New grease seals will also be needed.

SCRAPING NOISE FROM BRAKES Usually indicates metal-to-metal contact and the need for a long overdue brake job. Drum and rotor resurfacing will likely be needed in addition to new linings and brake hardware.

BRAKE SQUEAL Can be caused by vibrations between the disc pads and caliper, which can be cured by resurfacing the rotors, applying a nondirectional finish to the rotors after resurfacing, installing new pads and pad shims, or applying brake grease or noise compound to the backs of the pads.

BRAKE CHATTER Can be caused by warped rotors or rotors that have been improperly finished.

GRABBY BRAKES Oil, grease or brake fluid on the linings will cause them to grab. The cure is to identify and eliminate the source of contamination, then replace the linings. Badly scored drums or rotors can also grab. Resurfacing may be needed.

DRAGGING BRAKES May create a steering pull and/or increased fuel consumption. Caused by weak or broken retracting springs on drum brakes, a jammed or corroded caliper piston, a floating caliper with badly corroded mounting pins or bushings (uneven pad wear between the inner and outer pads is a clue here), overextended drum brake self-adjusters or a sticky or frozen emergency brake cable.

BRAKES PULL TO ONE SIDE Caused by contaminated linings, misadjusted brakes, a bad wheel cylinder or caliper, dragging brakes on one side or loose wheel bearings. Can also be caused by a mismatch of friction materials side-to-side on the front brakes or differences in rotor thickness, type or condition.

HARD BRAKE PEDAL Lack of power assist may be due to low engine vacuum, a leaky vacuum hose or a defective booster. Sometimes a faulty check valve will allow vacuum to bleed out of the booster causing a hard pedal when the brakes are applied. This condition can be diagnosed by starting the engine (to build vacuum), shutting it off, waiting four or five minutes, then trying the brakes to see if there is power assist. No assist means a new check valve is needed.

A quick way to check the vacuum booster is to pump the brake pedal several times with the engine off to bleed off any vacuum that may still be in the unit. Then hold your foot on the pedal and start the engine. If the booster is working, the amount of effort required to hold the pedal should drop and the pedal itself may depress slightly. If nothing happens and the vacuum connections to the booster unit are okay, a new booster is needed (the vacuum hose should be replaced, too).

On vehicles equipped with "Hydroboost" power brakes, a hard pedal can be caused by a loose power steering pump belt, a low fluid level, leaks in the power hoses, or leaks or faulty valves in the hydroboost unit itself (the latter call for rebuilding or replacing the booster).


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