What Calipers Do
Brake calipers, found only on disc brake systems, house pistons which use the force of hydraulic brake fluid to stop the vehicle. More specifically, those pistons squeeze brake pads against rotating disc brake rotors - creating the friction necessary for scrubbing off speed.
Calipers can contain a varying number of pistons, and come with either a "fixed" or "floating" mount design. Fixed disc brake calipers have pistons on BOTH sides of the caliper housing. They remain stationary because they're fixed in place over the center of the brake rotor. In contrast, a floating caliper housing, with a piston or pistons on only one side, will slide from side to side so that the piston(s) can apply pad pressure from both directions.
Generally, disc brake calipers are tough and durable. They have to be, because they endure grueling conditions whenever the wheels are turning. On modern vehicles, it's not uncommon for calipers to last at least 100,000 miles or 10 years. Because caliper life can vary significantly depending on how you drive, the climate you live in, and the humidity level in the air, automakers have always avoided making replacement recommendations at specific intervals. Instead, they advise checking the condition of calipers along with pads and rotors during routine maintenance checks.
The clear question is how do you recognize when new calipers are actually needed? It's good knowledge to have - considering new caliper parts can cost a few bucks, even if the labor isn't extensive. In this article, we'll look at what causes brake caliper wear, and we'll help you spot the signs of trouble.
Rebuilding vs. Replacing Calipers
In the old days, shops would rebuild worn-out calipers using new pistons, seals, guide pins, pin sleeves, guide pin covers & boots, and other items. The practice isn't so common any more because labor time has increased to the point where customers don't see the value in it. Plus, there's always the risk of a comeback if everything isn't installed in a meticulous, perfectly correct fashion. Today, it's more economical to install replacement calipers when old ones become too compromised to do their job. However, if new or remanufactured calipers are not available for your particular vehicle, then it's a good idea to check for the parts to have them rebuilt.
How Brake Calipers Wear
When calipers do their thing during the course of a standard drive, a huge amount of heat is generated. This heat radiates directly from the pads and rotors into caliper assemblies, where temperatures can reach over 300 degrees Fahrenheit.
Over countless heat-up and cool-down cycles, corrosion can form inside and outside of the caliper. This corrosion comes from many places: the moisture in the air, whether it's humidity or precipitation; and any moisture that may have been absorbed by the brake fluid, especially if it hasn't been changed at specified intervals (see our related article When Is It Time To Replace My Brake Fluid? to learn more about this subject).
Because temperatures inside a brake caliper exceed 212 degrees Fahrenheit, any water that's found its way into the brake fluid boils and turns to steam. Countless repeated cycles of water boiling, then condensing, then boiling again is what eventually gives corrosion a foothold.
Corrosion which forms on the caliper pistons or cylinder walls is likely to create rough surfaces that cause abrasive wear on seals as the pistons slide out and back during operation. Because the piston seals also dry up and harden with age, they are no longer flexible enough to withstand normal forces or scraping - so they start to leak.
If corrosion reaches a critical point inside a brake caliper, it may seize up and not move at all if pistons become stuck inside their cylinder chambers. The problem can be exacerbated by pads which have worn almost down to the backing plates, requiring the pistons to extend even further out of their caliper bores.
Floating Caliper Pins
As we mentioned before, "floating" calipers slide on guide pins from side to side over the brake rotor. As caliper pistons move outward, the inboard pad contacts the rotor first, causing the caliper to slide over until the outer pad makes contact with the rotor. When the brakes are released, the floating caliper self-centers itself over the middle of the rotor. Your vehicle owner manual may tell you whether your disc brake calipers are fixed or floating - but if not, a quick call to the manufacturer's headquarters should provide an answer.
If you do have floating calipers, it's important to inspect the slides, pins, and rubber bushings that are integral to their operation. The pins are subject to the same corrosion concerns as the pistons. Note that these items should be cleaned and "greased" periodically with brake lubricant paste, and they should be replaced whenever new calipers are installed. Usually, a new caliper includes such pieces.
A common failure with floating calipers is "stuck" guide pins which prevent the sliding portion of the caliper from moving. This leads to either a brake that won't apply, or a brake that is always applied. Neither case is good.
Signs Of Caliper Trouble
Pulling To One Side
A caliper that's binding up and not releasing can cause brake pads to drag, and the vehicle to pull to one side. When brakes are applied, the vehicle might pull noticeably toward the "good" side where grip is now stronger. Release the brake pedal, and you may notice a pull back toward the "bad" side that's still gripping because it hasn't released.
Uneven Pad Wear
Rusty or compromised slides or bushings may create a situation where a floating style caliper can't move freely and easily across its path of travel. As a result, brake pads will wear unevenly if proper contact isn't made when a caliper hangs up. Excessive wear on outer brake pads may result if brakes stick instead of releasing freely, since that side won't be pulled away from contact with the rotor. These specific problems are less of an issue with fixed brake calipers, since their position is completely stationary.
However, a fixed caliper may still see higher- or lower-than-normal wear on the side where a frozen piston is, depending on the position that the piston is stuck in. If it's jammed too far out, the pad on the bad side will wear more because it's always dragging against the rotor. If the piston is stuck too far in, the pad will wear less on the bad side because it never makes any contact with the rotor. In this case, you'll notice an unusual buildup of surface rust on the rotor which normally gets scrubbed off by the brake pad.
Brake Fluid Leakage
As we mentioned earlier, high heat levels and any corrosion from water buildup in the brake fluid will eventually cause rubber seals and boots around the caliper pistons to deteriorate and leak.
Depending on how bad a leak is, the affected caliper may or may not suffer from reduced braking pressure at that wheel - even if the pistons themselves move freely. When leakage reaches a certain point, any reduced pressure will cause the vehicle to pull away from the bad side when brakes are applied.
Of course, ANY brake fluid leakage is very dangerous, because if enough fluid leaks out, the vehicle may completely lose its hydraulic brake system.
Unusual Noise From The Brakes
If your vehicle's moving and you hear squealing or other frictional sounds from one of the wheels when brakes are not being applied, you've probably got a stuck caliper. If this is the case, the noise will probably go away temporarily during the time brakes are applied.
When stuck pistons are partially (but not fully) jammed in their cylinder bores, they may release in an unpredictable fashion. This can cause irregular levels of noise, grip, and it will likely cause some pulling.
Replace Calipers In Pairs
We'll take this opportunity to stress the importance of changing both front or both rear calipers in pairs - unless the unaffected one on the opposite side is relatively new. If it is, make sure you find an exact match of that caliper make and model to ensure it has the same number of pistons, exerts the same amount of force, and contains pads of identical makeup and thickness.
Assuming both calipers on the front or rear axle are of the same age and mileage, replace them both as a matched set. Even if only the right rear caliper is bad, for example, you should still replace both rear ones to ensure they perform equally and predictably together. That way, you know your vehicle will track straight and sure during hard stops. That left rear caliper may seem alright, but odds are it's just as worn out and will need to replacement soon.
Opportune Times To Replace A Brake Caliper
Whenever any brake work is being performed on your car, whether that's pads, rotors, or a fluid flush, the calipers should be thoroughly inspected for any possible needs. This is the most opportune time to check for corrosion, leaks, or any signs of damage. Obviously, pad/rotor replacement is the best time to also replace calipers.
Another opportunity is when brake rotors are removed to work on items behind them such as wheel hubs, bearings, axle shaft seals, or the axles themselves.
Since the brake system must be flushed with new fluid to bleed out air that enters the lines when calipers are changed, it therefore makes sense to replace calipers and flush the brake fluid as part of the same operation. Other brake system repairs that require a full fluid flush afterward are replacement of brake lines/hoses, master cylinder, or various anti-lock braking components.
Our article How To Replace Disc Brake Pads will help walk you through the steps of detaching a brake caliper from its mounting bracket, and how to lubricate sliding caliper pins. Plus, we recommend reading Special Tools Used In Brake Service to see what equipment you'll need ahead of time. For more details on bleeding out the brake system and putting new fluid in, we've also got some guidelines regarding performing a brake fluid flush.
Brake calipers are easy to take for granted. We tend to pay a lot more attention to brake pads and rotors as these are the most common disc brake system wear items. We hope this article gives you the confidence to understand the warning signs of brake caliper issues, and to shop for brake calipers and related tools yourself. But if you have any questions, we welcome your inquiries seven days a week.