Brake Pad Diagnosis

Brake pad diagnosis is an important skill for any car owner. Being able to tell when you’re brake pads need to be replaced or other work is required in your brake system is valuable automotive information.


Since brake pad maintenance is required on vehicles every 25,000 to 50,000 miles, this would mean that each vehicle owner might do as many as three to five brake jobs during the vehicle’s life span.

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In my last post I talked about a brake pulsation that was caused by warped rotors. In this post I will discuss brake pads, and how to tell when it’s time to replace them.

Brake pad diagnosis


There are several different types of brake pads as well as different types of wear indicators. let’s start off with the brake pad assembly itself. Brake pads are metal plates with the linings either riveted or bonded to them.

Brake pads are located at each side of the caliper and sandwich the rotor much like the ones on a 10-speed bike. The inner brake pad, which is positioned against the caliper piston, is not interchangeable with the outer brake pad.

The linings themselves are made of a semi-metallic or other non-asbestos material. Ceramic is becomming more popular due to longer life and less brake dust created when they wear.

The more metallic material contained in the brake pads, the longer the wear of the pad. This is a trade-off between noise and stopping distance.

The more metal contained in the lining presents more of a chance for brake noise as well as longer stopping distances.

If a brake pad is too soft it will often be quiet and stop the vehicle extremely efficiently. But also the brake pads will not last as long. ceramic brake pads offer a good compromise.

Brake pad wear sensors

Some brake pads have the wear sensor indicators built-in. The two most common designs of wear sensors are audible and visual.

Audible sensors are thin spring steel tabs that are riveted and installed onto the edge of the pads backing plate. These tabs are positioned to contact the rotor when the lining wears down to a minimum replacement thickness.

When the tabs contact the rotor a high pitched squeal, while the vehicle is moving will be heard. Note that when the brakes are applied often this brake squealing noise will disappear and then reappear when the brakes are released.

This wear sensor is designed to save the rotor from being destroyed by a metal-to-metal condition. It is also a safety warning to the driver that the brakes have reached the end of their life.

A visual wear sensor is to inform the driver that brake pad replacement is required by illuminating a dash light. These types of sensors are common on German high-end vehicles such as BMW or Mercedes Benz.

An electrical wear sensor is built directly into the pad and when the pads wear down the circuit is completed and the light is illuminated on the dash.

This is a great system, but it does increase the cost of brake pad maintenance. Also note that a good way to verify that your brakes are worn may be to inspect your brake fluid level.

As disc brake pad linings get thin more brake fluid is needed in the system. This will drop the fluid level in the brake fluid reservoir. This is a telltale sign that you’re brake pads are starting to wear and may need service.

Monitoring your brake fluid level will only work if you are sure that no one has added fluid during an oil change or other types of regular maintenance.

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