Diagnosing Brake Concerns

Apply firm steady pressure and hold. If the pedal slowly sinks toward the floor while you hold it — and there is no visible external leak — the master cylinder has an internal bypass. Fluid passes past the worn piston seals inside the master cylinder instead of holding pressure. Replace the master cylinder. If there IS a visible fluid leak — find and repair the leak first. Any brake fluid leak is a safety emergency.

A vibration felt through the brake pedal during braking. Measure rotor lateral runout with a dial indicator mounted to the caliper bracket — specification is typically under 0.002 inches. Measure rotor thickness at eight evenly spaced points — variation above 0.0005 inches causes pulsation. If runout or thickness variation is out of spec, machine or replace the rotors.

After a test drive, carefully feel the temperature of each wheel or rotor with an infrared thermometer. The side that is hotter is doing more work. The side that is cooler is the problem side — a caliper that is not applying fully, a collapsed brake hose restricting fluid flow to that caliper, or contaminated brake pads on that side. A caliper that is sticking or seized is the most common cause of a brake pull.

Metal-to-metal contact. The brake pad friction material is completely worn through and the steel backing plate is grinding against the rotor. This is a safety concern requiring immediate inspection. The rotor is likely damaged and may need replacement along with the pads. Never tell a customer grinding brakes can wait.

Scan the ABS module for codes. The most common ABS codes are wheel speed sensor codes — a specific wheel sensor has lost signal or is reading erratically. Check the sensor air gap, the tone ring for damage or debris, the sensor wiring for damage, and the sensor connector for corrosion. A wheel bearing with excessive play also causes wheel speed sensor codes because the tone ring wobbles relative to the sensor as the bearing moves.