What Is a Brake Caliper, Anyway?
The brake caliper plays a central role in a disc-brake system and has two functions. First, it acts either as a bracket to support the brake pads on either side of the rotor or to support the caliper bracket itself — there are other designs, but these are the two most common. Second, it uses pistons to convert pressure exerted on the brake fluid by the master cylinder into friction on the rotor.
In simple terms, a brake caliper’s purpose is to squeeze the brake pads against the rotor to stop the car. There are two main types of calipers, a single piston and a dual piston. Most front calipers are dual piston but many cars use single piston calipers on the rear, where less braking force is needed.
Stepping on the brake pedal forces the master cylinder piston forward, compressing the brake fluid. The brake fluid forces the caliper pistons toward the rotors, pinching the rotors in between the brake pads, which creates friction and slows the vehicle.
When Brake Calipers Go Bad
In general, brake pads and rotors wear out and need replacement far more often than calipers. A leading cause for damaged calipers, however, stems from driving a vehicle on worn-out pads or warped rotors. (Find out how to change front brake pads.) Both prevent the system from dissipating the heat of friction, as they’re designed to do, which can damage the calipers.
If the pads fail to insulate the caliper from excessive heat, the piston can be damaged or the heat can be passed through the piston to the brake fluid, which can cause it to degrade. The latter can result in brake failure.
A damaged piston, or one that is simply corroded, may get stuck in one position. If it sticks in the retracted position, that wheel will lose braking ability. If it sticks in the engaged position, the wheel will brake continuously until freed.
How to Tell That a Caliper Has Failed
With a retracted piston, the car may pull toward the side of the car with operating brakes when they are engaged. You may also notice that braking distance increases. Conversely, an engaged piston will cause the car to pull toward the engaged brake when driving. (Note: A stuck caliper can cause pulling, but there are many other possible causes as well.) Excess heat will be present, and the brake pad will quickly wear down. Any of these symptoms indicate immediate need for service. (Here’s what to do if your car shakes when braking.)
Another sign of caliper failure could include leaking brake fluid, as a damaged piston may no longer seal completely. If enough fluid escapes from the system, the warning light on the dashboard will call your attention to it. If you check your pad wear regularly, you may note uneven wear on the pads, comparing one side of the rotor to the other, or even left wheel to right wheel. If the pads show uneven wear, check the caliper function. And yet another sign of a seized caliper is excessive brake dust on one wheel compared to the other.
In the rarest form of failure, the caliper bracket could snap, causing a clunking sound when the brakes engage. If you hear this, stop immediately and do not operate the vehicle. (Here are nine more strange car sounds—and what they could mean.)
Ignoring any of these symptoms can magnify the damage. The cost and effort required to address the problem increases proportionally. Make an effort to examine the problem as soon as possible or have it evaluated by a qualified technician. (Find out more car problems you’ll regret ignoring.)
Important Maintenance Points
- As the brake pads wear, the caliper needs to stay centred on the rotor to allow for even pressure on both sides. There are different ways manufacturers accomplish this, and some designs are better than others at keeping the calipers sliding to compensate for pad wear. When brake service is done, always clean and grease the sliding mechanisms with a high-temp brake grease to preserve the full range of travel. If not properly lubricated, calipers can lock in one position, resulting in only one pad getting proper pressure on the rotor.
- Whenever possible, inspect the dust boots protecting the caliper piston and the two slide pins. These flexible covers prevent dirt and moisture from fouling the action of the associated parts. Any damage or tears found in the boots must be addressed quickly, before dirt and corrosion cause the parts to seize. It is possible to disassemble the caliper, clean the parts and replace the boots if you have some skill as a DIYer. Labour charges, however, make this impractical in most auto shop situations, so the most common resolution is full replacement of the caliper and bracket.