With all the hoopla going on about the GM Brake Repair Litigation Settlement (on 1988 - 1993 Chevy Lumina, Buick Regal, Oldsmobile Cutlass Supreme, and Pontiac Grand Prix automobiles), I thought I'd dedicate a column to disc brakes ... what they are, how they work, what causes them to fail, and proper maintenance.
First, let's take a brief look at the Class Action Suit against GM, which was settled in August of 2000. What are you entitled to as an owner of one of these vehicles (providing you got your claim in before the due date, postmarked no later than Oct. 27, 2000)? To find this and any other information about the settlement, call toll free at 1-888-439-4793.
Exactly what was the problem with the above mentioned vehicles? The rear brake calipers (and, infrequently, the front brake calipers) were seizing because the caliper slide pins were rusting up, due to exposure to weather elements (preventing the brake calipers from moving). Depending on the point at which they froze up, the calipers either stayed applied and would not release, or they were not applied at all after the brake pedal was depressed. In the first scenario, if they stayed applied, the brakes wore out prematurely, because the friction from the stuck calipers wore down the brake pads. In the second scenario, when the calipers froze at the point where they were not applied, then the rotors would rust and the calipers would seize internally. As a result, the other set of brakes not involved in this process would wear out prematurely. Why? Because all the responsibility for stopping the car was saddled on those brakes that were working correctly. Either scenario usually resulted in expensive brake repairs.
Let's take a look at the basic disc brake system and how it works ...
- The components:
- Master Cylinder
- Steel brake lines
- Proportioning valve
- Brake calipers
- Brake rotors or discs
- Brake pads, anti-rattle hardware, and siding mechanisms (IE: pins)
1. The master cylinder is mechanically connected to the brake pedal through a system of steel rods called linkage. These rods operate at different angles using bushings that are usually made of nylon, rubber, or Teflon. When you step on the brake pedal, the linkage pushes on a steel rod that pushes into the back of the master cylinder. The master cylinder is nothing more than an elaborate pump that forces brake fluid through the braking system to energize the various components that stop your car.
2. The steel brake lines are the infrastructure that provides a pathway for the brake fluid to travel through to do its job.
3. The Proportioning valve measures and adjusts the amount of fluid that goes to the front Vs back brakes, because each set of brakes require different volumes and pressures to equally brake and stop the car.
4. The brake calipers are nothing more than powerful "C" clamps that are actuated by hydraulic pressure which occurs when the driver depresses the brake pedal, creating hydraulic pressure within the system. The calipers have large pistons inside of them that, when brake fluid pushes behind them, are forced outward ... creating a clamping action on the pads, which are in contact with the rotors.
5. Brake rotors or discs are flat round steel discs that are attached to the car's wheels. The calipers straddle over them and, when the brake pedal is depressed, the calipers clamp down on them, causing the brake pads to make contact with the rotors, creating friction and thus stopping the car.
6. Attached to the calipers are brake pads. They are the friction material that is needed to stop the forward motion of the wheels. Specifically, these pads are made of steel backing with friction material affixed to it, either by the use of industrial grade glue or steel rivets. Anti-rattle hardware consists of spring-steel clips that are affixed to the brake pads to keep them in place on the brake caliper. Without this hardware, the pads would rattle, causing clicking and squealing noises when the wheels are in motion. The sliding mechanisms are usually pins upon which the calipers slide. They are attached to the steering knuckle in such a way as to position the brake calipers so that they straddle the disc with the pads attached to them. When the brake pedal is depressed, the hydraulic pressure generated within the system forces the piston within the caliper outward; this causes the brake pads to clamp onto the discs, creating the friction necessary to stop the forward motion of the wheels. The sliding mechanisms must be clean, lubricated, and moveable for the calipers to apply and release the brake pads on the discs.
In addition, on cars equipped with four-wheel disc brakes, the emergency brake cables must be kept free and moving, because it is the emergency brake cable that actuates the e-brake. If the cable freezes up due to rust or fraying, the emergency brake, when applied, will not release. An e-brake that is frozen in the applied position will cause the brake pads to heat up and prematurely wear out. It will also cause rotor warpage because of the intense heat generated from friction.
Disc brakes need to be checked over every six months. If your car is equipped with four-wheel disc brakes, have the caliper pins and emergency brake cables checked, because this is an Achilles' tendon on such cars! This inspection should include checking the caliper pins for rust or dirt, and broken weather protector seals that would let the weather elements and salt into the slide pins, causing oxidation. In addition, check the cables themselves, as they have a tendency to rust and seize due to exposure to the weather.
When replacing brake parts, use the best quality parts available. The brakes stop your car! Using cheap parts compromises your family's safety! The old sayings, such as ... "You get what you pay for" and ... "A penny wise and a pound foolish" come to mind. Be wise and ... good stopping!
'Til next time ... Keep Rollin'