Diagnostics for an Auto Brake Problem

The brake systems on modern automobiles are both effective and reliable; however, from time to time problems can arise. Normally there will be warning signs before a problem develops into a catastrophic failure, and it is important to learn how to identify and interpret these symptoms so that developing brake problems can be nipped in the bud.

Brake Noise

A high-pitched squeal, when braking, may be caused by the wear indicators that some manufacturers build into the inside disc brake pads to make this warning sound when the pads begin to thin. If the pads are old, check the lining thickness. If the brake pads are new, wait until the vehicle has been driven for about 500 miles to allow the new pads and the discs to wear in together. If the pads are neither new nor old, consider installing soft shims on the backs of the brake pads. Often brake noise is caused by the accumulation of dirt and dust on the brake, and a simple cleaning can solve the problem. If a very loud crunching, scraping or grinding is heard, this most likely indicates a complete failure of one or more of the brake pads, in which case the failed pad(s) must be replaced as soon as possible.

Brake Pull

If the vehicle pulls to one side or the other when braking, this usually means that the caliper on the side opposite to the direction of pull has seized up. Brake pull can also be caused by restricted or plugged brake lines, or by a failure of one chamber of the brake master cylinder. The brake pads on the side opposite to the pull may possibly have oil on the lining surface. If the pull is accompanied by a loud grinding noise, this usually means that the brake pads on the side of the pull have failed completely. Other possible causes include poor front-end alignment and improperly inflated or mismatched tires.

Vibration or Pulsation During Braking

Vibration, during braking, is often the result of a misaligned brake disc or an out-of-round brake drum. It can also be the result of a cracked disc or drum, or a loose caliper or brake shoe. Uneven wear on the brake pad or shoe linings can also cause vibration.

Grabbing Brakes

If the brakes grab suddenly, this can indicate problems with the vacuum booster or the proportioning valve. This may also be caused by contamination on the brake pads or shoes. On occasion, dust and road grit can build up on the pad linings, causing increased friction between the pads and the rotor. This often happens after extended driving on dusty dirt roads.

Soft Brake Pedal

If the brake pedal feels soft or mushy when pressed, it can be a sign of low brake fluid level in the brake fluid reservoir. Soft brakes can also indicate that air is trapped in the brake lines or master cylinder. This can also be caused by a defective or loose master cylinder. If the brake pedal actually sinks down to the floor, this indicates that either the brake fluid level is critically low or the master cylinder is defective.

Hard Brake Pedal

If the brake pedal feels hard and high, and you must push harder than normal on the pedal, this indicates a problem with the brake vacuum booster.