How to Check Brake Wear

Modern automotive brake systems are effective and reliable. The brakes work by generating friction, and the various parts involved will wear out over time. Brake pads and shoes wear out regularly, and over time the brake discs and drums may wear out as well. In order to ensure proper operation of the brakes at all times it is important that these wear-prone components be checked regularly and replaced as necessary. You can save both time and money by learning how to check brake wear yourself.

Instructions

Park the vehicle on firm and level ground. Put automatic transmissions in park, and put manual transmissions in first or reverse gear. Set the parking brake. Securely block the front wheels if servicing a rear brake, or the rear wheels if servicing a front brake. Partially loosen the lug nuts on the wheel to be serviced about one full turn each. Jack up the car and set it securely on a safety stand. Finish removing the lug nuts and pull the wheel off.

Measure the disc thickness at several places with a brake disc micrometer. Compare the measurements to the minimum allowable thickness as stamped into the metal of the disc, usually at the rim.

Measure the thickness of the brake pad linings using the finely graduated ruler. You can measure the thickness of the inner part of the lining. The outer part of the lining can be accessed through the inspection opening in the brake caliper frame. Compare the measured thickness to the manufacturer's recommended minimum thickness. This can be found in the vehicle shop manual or an aftermarket repair manual. These are usually available at the local public library. You can also ask at your local auto parts store.

Park the vehicle on firm and level ground. Put automatic transmissions in park, and put manual transmissions in first or reverse gear. Set the parking brake and securely block the front wheels. Partially loosen the lug nuts on the wheel to be serviced about one full turn each. Jack up the car and set it securely on a safety stand. Finish removing the lug nuts and pull the wheel off. Release the parking brake.

Remove the brake drum. On many vehicles it will pull right off the hub, but sometimes it may be held to the hub assembly by retaining screws or bolts. If so, remove the retaining fasteners before pulling the drum off. The drum may also be held by a large hub nut, in which case this must first be removed before removing the drum. If the drum is seized to the backing plate, firmly tap the drum with a rubber or plastic mallet to loosen it. Take care not to hit the drum so hard that it cracks.

Measure the inside diameter of the brake drum in several directions using a drum micrometer. The diameter should be equal in all directions, indicating that the drum is round. Compare the measured diameter to the manufacturer's recommended maximum diameter. This information can be found in the appropriate shop manual or aftermarket equivalent repair manual. If no manual is available, the maximum allowable drum diameter is normally stamped into the metal of the outside of the drum.

Measure the thickness of the brake shoe linings with a finely graduated ruler and compare to the manufacturer's recommended minimum. This information can be found in the vehicle's shop manual or aftermarket repair manual, or you can ask at an auto parts store.