How to Fix a Low Brake Pedal

by KevinM
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disque de frein image by Christophe Fouquin from

The braking system is critical to automotive safety. Our lives, and the lives of others, depend on proper functioning of the brakes on every vehicle on the road. Brake systems do fail, so you must perform regular preventive maintenance and pay attention to the early symptoms of developing problems. One such common symptom is a low or soft brake pedal. This occurs when you must depress the brake pedal much farther than expected before the brakes engage. This gives you the uncomfortable feeling that your vehicle may not stop.

Step 1

Determine if the low brake pedal is accompanied by vibration or pulsation when braking. If so, it is likely that a warped brake disk or an out-of-round rear brake drum is pushing the brake pad or shoe farther away from the braking surface than normal. This means that the brake pedal will have to be depressed farther than normal before the brakes engage, making the pedal feel soft and low. Any vibration or pulsation in the brakes is cause for an immediate complete inspection. Be sure the disks and drums are all true and round, and that the pads and shoes (and all other brake components) are in good condition.

Step 2

Think about how the problem developed. Did it start suddenly, or gradually? If the problem started suddenly after brake servicing, air likely is in one or more of the brake lines. Bleed the lines to remove the air. If the problem started suddenly and nobody has serviced the brakes for awhile, the problem is likely caused by a fluid leak in the system or by a problem with the master cylinder.

On older drum brakes, a low brake pedal can sometimes develop if the self-adjusting mechanism is corroded and sticking. If your car has older drum brakes (many low-end cars still have rear drum brakes) try backing up quickly and braking firmly. This action might loosen up the self-adjusting mechanism and fix the problem.

Step 3

Check the brake fluid level in the master cylinder reservoir. A low brake pedal often means you don't have enough brake fluid in the reservoir. Look inside. You should see a maximum and a minimum level marked on the side of the reservoir. The level should be between these two marks. If the master cylinder reservoir level is low, add sufficient new brake fluid to bring the level up to about halfway between the min and max marks.

Step 4

Check the appearance of the brake fluid in the master cylinder reservoir at the same time that you are checking the fluid level. The fluid should be reddish in color and it should have a clear appearance similar to most cherry cough syrups. If the fluid looks brownish, if scum is floating on the fluid surface or if the fluid looks as if it has any kind of solid or liquid contamination, drain all the fluid, flush the system and refill with new fluid.

Step 5

Thoroughly inspect the master cylinder, the brake lines, and the brakes themselves for signs of leakage. If the brake fluid level is low, it must be going somewhere--and this stuff doesn't evaporate. A slightly low fluid level may simply be caused by worn brake pad or shoe linings, but a very low level or a level that keeps going low after the reservoir is topped off is surely a sign of a leak in the system. Locate the leak and deal with it accordingly. Tighten loose connections and replace leaking lines and seals. Common leak locations include the connections between brake lines and the master cylinder, the brake lines at the calipers, and the rubber caliper piston seals.

Step 6

Test the master cylinder. Open the master cylinder reservoir cap and remove the brake fluid from the cylinder using a syringe or baster. If the fluid is in good condition, save it in a clean container for reuse. Carefully remove the brake lines from the bottom of the master cylinder and securely plug the line connections on the master cylinder with suitable caps or plugs. Refill the reservoir to the appropriate level, replace the reservoir cap, start the car and apply the brakes. If the brake pedal now feels firm and high, the master cylinder is functioning properly.

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