DIY

How to Diagnose a Faulty Brake Caliper

Reading Time: 5 minutes

Before spending your hard-earned money on a new caliper, you’ll want to make sure the old one is bad. The good news is that caliper diagnosis is straightforward and doesn’t require fancy equipment.

Brake Caliper Inspection Methods

Caliper diagnosis isn’t as difficult as you might think. If you’re ready and willing to get dirty, there are several methods you can use to troubleshoot a bad caliper.

Note: The following are general guidelines for educational and entertainment purposes only. Consult your vehicle’s factory information for specific repair instructions and recommended safety procedures.

1. Inspect for Leaks

Got a low or spongy brake pedal? One of the most common causes is a leaking caliper, so the first step in your diagnosis is to look for leaks. Check the areas around the caliper piston as well as the bleeder screw for signs of fluid loss.

brake caliper leak
Look for brake caliper leak if you have a low or spongy brake pedal.

2. Look at the Brake Pads

A stuck brake caliper or sticking caliper sliders can cause uneven brake pad wear. To check for this, safely raise and support your vehicle, remove the caliper and take a look at your brake pads.

comparison of thick brake pads and thin brake pads because of uneven wear
If one of your brake pads is much thicker than the other and you have floating calipers, the slider bolts or slider pins are probably sticking.

Is one pad much thicker than the other? If your car has floating calipers, uneven pad wear usually indicates that the slider bolts or slider pins are sticking. Check that the sliders move freely. If they don’t, clean and lubricate them to restore proper operation.

If you find uneven pad wear, but the sliders are OK (or your car has fixed calipers without sliders), you’ll want to move on to the next step: checking caliper piston operation.

A stuck brake caliper or sticking caliper sliders can cause uneven brake pad wear.

3. Check Piston Operation with a Tool

A stuck piston is another common caliper problem. A piston that’s stuck in the applied position (out of its bore) can cause brake drag, uneven brake pad wear, and a vehicle that pulls to one side.

There are a few ways to check for this condition. Start by safely supporting the vehicle on jack stands and attempting to turn the wheel/tire assembly by hand. If the wheel is hard to turn, you may have a caliper that’s sticking and pushing the pads against the rotor.

You can also check the caliper piston by trying to push it back into its bore. Here’s how it’s done:

a faulty brake caliper leaking on a wheel
Found a leak on your wheel? Check if you have faulty brake calipers.

Note: Some calipers require a special wind back tool to push the caliper piston back into its bore. This tool is often required on rear calipers that have an integrated parking brake. Also, in some instances, a scan tool is required to put the brake system in service mode. Consult the factory repair information for your vehicle before performing this test.

But wait – if the caliper can’t be pushed back into its bore, how do you rule out a restricted brake hose? Crack the bleeder screw on the caliper and try pushing the piston back into its bore. If the piston still doesn’t move, the caliper (not the hose) is probably to blame. It’s also possible that the bleeder screw is restricted.

Warning: After reinstalling the brake caliper, make sure to pump the brakes until they’re firm. DO NOT drive the car until the brakes feel solid.

Only pump the brakes after everything is reassembled and the car is on the ground. If you pump the brakes with the caliper removed, the caliper piston will come shooting out.

Safely raise the vehicle and support it with jack stands. Have your buddy apply the brakes while you monitor caliper operation.

4. Check Piston Operation with a Buddy

A piston that’s stuck in the retracted position (inside its bore) can cause problems such as a low brake pedal. If you have a friend handy, you can check that the piston moves both in and out properly. Simply have your buddy apply the brakes while you monitor caliper operation.

Not only does this procedure ensure that the caliper piston is moving inward, but it allows you to see if the piston is moving outward as well.

5. Attempt an Advanced Line Lock Test

But wait – there’s more. Although some DIYers shy away from the more advanced line lock test (because the brake hoses can be damaged), it’s sometimes used by professionals.

When there’s a soft brake pedal concern, this method can be useful for isolating a bad caliper. A special brake hose pinch tool (a.k.a. line lock tool) must be used to prevent damage to the brake hoses. A set of regular vise grips should not be used.

tracing leak to a faulty brake caliper
A leak on surrounding brake parts could indicate a faulty caliper.

The process involves pinching off the brake hoses from the calipers one at a time. If the brake pedal firms up when one of the hoses is pinched off, the corresponding caliper may be faulty. You’ll want to inspect it further for leaks and other issues.

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Author

Mia Bevacqua

Chief Mechanic at CarParts.com

Mia Bevacqua is an automotive expert with over 15 years of industry experience. She holds ASE Master, L1, L2, and L3 Advanced Level Specialist certification, as well as a bachelor's degree in Advanced Automotive Systems.

Throughout her career, Mia has applied her skills toward automotive failure analysis inspections, consulting, diagnostic software development, and of course, freelance writing. Today, she writes for companies around the world, with many well-known clients showcasing her work.

Mia has a passion for math, science, and technology that motivates her to stay on top of the latest industry trends, such as electric vehicles and autonomous systems. At the same time, she has a weakness for fixer-upper oddballs, such as her 1987 Chevy Cavalier Z-24 and 1998 Chevy Astro Van AWD.

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