You’ve noticed, when applying the brakes, that the brake pedal moves up and down under light pressure and that you (may or may not) feel a slight shimmy in the steering wheel. What is it?
The answer is: you probably have a warped brake rotor or rotors.
Some cars are worse than others where warped rotors are concerned.
Disc brake pads are in constant contact with the rotors. Pads and rotors can run extremely hot, as can be seen if you’ve ever watched “under the car” shots of brakes on race cars. The rotors will be glowing red and the same can be true with passenger cars and trucks, especially if you’re towing, hauling a heavy load, going downhill, on a crooked road or any driving situation where you’re using the brakes a lot.
In the past, when cars and trucks only had drum brakes and we ran through water that got the brake shoes wet, it wasn’t unusual to have lots of pedal, but no brakes. Disc brakes eliminated most of that problem and the majority of brake fade that was also associated with drum brakes. Now, with disc brakes, if the rotors are hot and we run through water cooling the rotors too quickly, the rotor will warp. If you heat a piece of metal and then quickly place it in water, you can see the effects of quenching. The metal will twist, move and warp until it cools to the approximate temperature of the water. This is the process used when tempering metals. It makes the outer surface hard, and if done correctly, it leaves the inner parent metal pliable. But, the item has to be machined flat if precision is necessary, as is the case with disc brake rotors.
Running through water isn’t the only reason rotors warp.
If the piston in the disc brake caliper isn’t releasing properly, the brake pad will put too much pressure on the rotor and the ensuing friction won’t allow the rotor to cool. There are different types of calipers and caliper mounts, and some are more prone to sticking than others. Some cars have calipers that slide back and forth on the part that’s bolted to the wheel spindle assembly. If enough dirt or road grime gets between the sliding parts, the caliper can stick and not allow the pad sufficient clearance for cooling.
If you’re experiencing a “pumping” of the brake pedal, or a shimmy in the steering wheel when applying the brakes, you need to have the front brakes and rotors checked. If the rotors are warped, they need to be surfaced or replaced, depending on how worn they are, and the cause needs to be found. If the problem was caused by sticky brake caliper pistons, the calipers need to be rebuilt, which isn’t a bad idea anyway. If the slides are gummed up with dirt and road grime, they need to be properly cleaned and serviced. Be sure the mechanic is qualified to do the work. If you have brake problems, your life can be in danger.
If you wash your car at a pressure car wash, you can wash the brakes out using the pressure wand. Be sure to let the car sit for a few minutes or do other cleaning jobs before hosing off the brakes. If the brakes are hot and you wash them too soon, you can warp the rotors. Some cars have front mounted calipers and on others the calipers are mounted on the rear of the front brake spindle assembly. You should be able to see the caliper casting by looking through the slots in the front wheels. The rotor is a big disc and the caliper mounts over and around it. The brake pads are mounted inside the caliper, between it and the rotor.
Direct the high pressure water through the slots in the wheel and onto the caliper casting. You’ll see black dirt, actually brake pad dust, and road grime being washed out and onto the ground. This will help eliminate brake problems caused by road grime and dirt but will not cure any problems associated with sticking caliper pistons. If you’ve been experiencing squealing noises when applying the brakes, you may find they’re gone after you’ve washed the brakes. Dirt between the pads and rotors is often the cause of brake squeal. Grinding noises when applying the brakes are usually an indication that the pads are worn out and you need to have brake work done immediately.
Warped rotors can be dangerous, especially in panic stop situations. If you have problems with your brakes, have a qualified mechanic check them. The information in the above article isn’t meant to make you a mechanic, but it can help you be better informed and less likely to get a misdiagnosis or a big bill for work that wasn’t done
I was in the automotive parts, repair and race car business for years, and there are a lot more parts replacers around than there are mechanics.
