Brake Myths: Common Misconceptions

There are some myths that can hinder a technician’s ability to diagnose and solve some brake problems that need to be busted. On the surface, some of these myths make sense and explain a problem, but don’t resolve the real issues with a brake system.

1. A Rotor’s Minimum Thickness Specifications are Based on Heat

Brake Pad and Rotor Cross Section

False. The discard/minimum thickness specification is based on travel of the caliper piston if the pads were worn to the backing plates. If the pads and rotor are worn below this specification, the piston could start leaking and become dislodged from the bore causing a brake system failure. Heat, Warping, and fading have nothing to do with discard specifications.

2. Soft and Hard Pads

Hard and Soft Brake Pads

False, with engineering truth. Engineers measure compressibility as a quality control measurement, not as a performance measurement. Soft and hard pads are just different methods of getting friction between pad and rotor. Hard pads are rough and use their rough surface to create friction. Soft pads generate brake torque using adhesion friction. They coat the rotor surface, and grip the coating to preventing rotor wear. Calling one type soft or hard isn’t possible unless tested in a compressibility measuring machine.

3. Damaged Brake Hose Can Cause Brakes to Drag

Brake Hydraulic Hose

False, with some truth. This myth usually occurs on a vehicle where the brakes are only stuck on one wheel. The technician tries just about everything and theorizes its a hose restriction. Brake hoses are designed with multiple layers to take all kinds of abuse from road debris. The myth states that the liner was damaged creating an internal check valve that doesn’t allow the pressure from releasing the caliper. If this happened, the outer liner would break and leak fluids. The restriction is most likely caused by a stuck emergency break, caliper slides, or even a metering/combination valve problem. Updated “Damaged Brake Hose Can Cause Brakes to Drag” section. 

4. Wet Brake Rotors Increase Stopping Distances

Car Driving Through Water

False. This doesn’t happen to rotor brakes due to centrifugal force throwing the water off of the rotor. Drum brakes, on the other hand, do suffer from water on the surface.

5. Replacement Brake Pads are Regulated by the Government

 National Highway Traffic Safety Administration - US Department of Tansportation

False. There are no government regulations concerning brake pad performance.

6. Brake Pads Need to Warm Up

Racing Brake Pads Heating Up

False. Street brake pads produce torque at even very low temperatures, even the exotic carbon ceramic brake systems. The exception is brakes used on high-performance racing vehicles. These pads need heat to generate their highest coefficient of friction.

7. Pads Are The Source of All Brake Noise

Vehicle Cross Section

True and False. All pads make vibrations when applied, but it’s how the vibrations are transferred to the rest of the vehicle that causes noise. Consistent friction materials produce much less vibration by having consistent brake torque at environmental extremes of humidity and temperature. (-40F-500F). Typically high frequency noise comes from the rotor, caliper and bracket while low frequency noise comes from struts, knuckles. or body structure. Technicians can use lubricants, shims, and new hardware to reduce noise.