When we hear anybody talk about brakes they usually are talking about brake pads or shoes. For some reason pretty much everything else in the system seems to get ignored. We have seen this over and over leading to complaints such as horrible noises, excessive black dust on wheels, vibrations when brakes applied, poor braking, pulling to one side, poor fuel economy, premature wheel speed sensor failure, premature wheel bearing failure, brake fade or failure and crashes!
To understand why this occurs you need to understand how brakes actually function. The law of conservation of energy basically states that energy cannot be created or destroyed only changed. What brakes do then is through friction convert the kinetic energy of the moving vehicle to heat. The heat must then be handled for the vehicle to stop properly. In other words the brakes are designed to get hot and the heat has to go somewhere.
How a disk brake functions:
The master cylinder is a pump so that as you step on the brake pedal, brake fluid pressure is directed to the back of a piston in the caliper. The piston can move inside the caliper as well as the caliper can moving on it’s mounts. This allows the caliper to squeeze the friction material (pads) onto the rotor creating
the braking action. The seal on the caliper piston is square cut and fits very tight to the piston. When the piston moves it causes the seal to deflect or twist. When you take your foot off the brake pedal the seal will relax and pull the piston back a little bit releasing the caliper and allowing the wheel to spin freely. In the old days friction material was made using asbestos which is a heat reflector so most of the heat generated was absorbed and dissipated by the rotor. However on today’s vehicles the friction material is made out of a metallic or better yet ceramic material. These materials conduct heat away from the rotor and dump it into the caliper. This allows the manufacturers to use a lighter rotor reducing the vehicles un-sprung weight for better ride control and handling. However since the caliper now gets heated a new problem arises. Imagine putting that poor little seal through thousands of heat and cool cycles; eventually it loses it elasticity so instead of flexing with the piston the piston slides inside of it. You now take your foot off the brake pedal and the caliper does not release. This is like driving around with your brakes on all the time. Some of the symptoms this can cause are:
- Overheating of the rotors which then warp and in turn cause a brake vibration.
- Overheating of the friction material causing flaking and pad failure.
- Brake pedal fade.
- Premature friction material wear out.
- Excessive black dust on wheels.
- Overheating of wheel bearings leading to premature failure.
- Overheating of delicate wheel speed sensors leading to failure.
- Overheating of constant velocity joints and boots leading to premature failure.
- Overheating of brake hoses leading to premature failure.
- Excessive fuel consumption.
Of course there are all kinds of other things that can go wrong in a brake system especially when you factor in antilock, traction control and ride control systems, however this one is easy to test for yet seems to be the most missed most of the time.
How to determine if your vehicle has a caliper problem:
- Inspect disc brake looking for uneven wear on the pads.
- Both brake pads in the caliper should have even wear between them and across the face of the pad.
- Excessive inner pad wear indicates a caliper piston not releasing properly.
- Excessive outer pad wear indicates sticking or siezed caliper sliders.
- Uneven wear across a pad face may indicate worn caliper sliders.
- Drive the vehicle and get the brakes warmed up then lift the vehicle on a suitable lifting device such as a hoist.
- Remove the wheel and have a person apply and release the brakes observing the caliper action.
- You should see the caliper piston move out and the brake should apply.
- While letting up on the brake pedal you should see the caliper piston pull back a bit and the wheel should spin freely.
- You should be able to “grab” the caliper and easily move it back and forth a little bit in its mount. CAUTION: remember brakes get hot, it is very easy to burn yourself.
Now when you hear someone say “Man, I had my brakes done a short time ago and they just don’t feel right” you can say “ahhh yes, did you know? …”
