Car Callipers – What Are They and How Do They Work?
There are basically two kinds of brake systems: disc brakes and drum brakes. Drum brakes are an older technology, not as powerful nor as efficient, but still in use in some applications because they’re cheaper to produce and pretty good for rear brakes in most vehicles. Disc brakes are a newer technology, better than drum brakes in every way, but also more expensive to produce and maintain.
Where does a calliper come in, though? The disc brake system is made up of a few basic parts, including the brake calliper, brake rotor, brake pads, and various shims, springs, and clips to hold the pads. The brake rotor, or brake disc, mounts between the wheel and axle hub, rotating with the axle and wheel. The brake calliper is fixed to the steering or suspension knuckle. Gripping the rotor, the brake calliper can reduce the speed of the wheel to the speed of the steering or suspension, that is, zero – more on that in a minute.
Brake callipers come in two basic types, fixed brake callipers and floating brake callipers. Fixed brake callipers are bolted directly to the knuckle and all moving parts are internal. Inside the block of a fixed brake calliper, two to four pairs of pistons compress the brake pads, which slide on pins, from both sides. Floating brake callipers are not mounted directly to the knuckle, but to a “cage.” The cage carries the brake pads, usually on sliding rails, and the brake calliper slides over them, mounted with sliding bolts. Inside a floating brake calliper are one or two pistons on the inboard side.
What Do Callipers Do?
At their most basic, brake callipers are force-multiplication devices. Step on the brake pedal and a small piston compresses brake fluid in the master cylinder. Because brake fluid doesn’t compress, this force is transmitted instantly to the brake callipers. Inside the brake calliper, large pistons multiply the force exerted, pushing the brake pads into the brake rotor.
In the case of fixed brake callipers, the pistons compress from both sides. In the case of floating brake callipers, the piston pushes first on the inboard brake pad, pushing the calliper away from the rotor, causing the outboard brake pad to contact the rotor. The calliper slides allow for this movement.
Can Callipers Fail?
In short; yes they can.
- Stuck Calliper Slider: On floating callipers, calliper sliders are the weakest link and cause many problems. Accelerated wear on the inboard pad is common enough, but a sticking slider exacerbates the problem. If the calliper slider can’t move freely, it could lead to more wear on the inboard pad, dragging of the outboard pad, or reduced braking efficiency, no braking at all on the outboard pad. If one of the sliders is sticking, this might lead to a spongy brake pedal feeling, as the brake calliper flexes trying to make full contact with the rotor.
- Leaking Caliper Piston: In fixed or floating calipers, each piston has a square rubber seal, which holds brake pressure and pulls the piston back slightly on release. An external rubber boot keeps water and dust out of the piston bore. Due to age or poor installation practices, torn dust boots could allow water and dust into the piston bore, accelerating corrosion. If the piston seal passes over this corrosion, it will likely be damaged and leak.
- Sticking Brake Pad: There are tight clearances between the brake pads and retaining hardware. This keeps things from bouncing around and making noise. Reduced clearances also make for more efficient braking. Over time, corrosion can reduce this clearance, causing the brake pad to drag or stick. A sticking brake pad may drag on the brake rotor or not move to engage the rotor, leading to accelerated wear, overheating, and inefficient braking. A sticking brake pad can mimic a stuck slider in the way it feels and acts.
The best way to assess a calliper issue is to take it to the pro’s; why not get in touch with us for a quote today?
h/t to thoughtco.com for the great info!