Braking System

Brake Caliper Piston Won’t Compress

Mike Cross
Updated Aug 10, 2021
Brake Caliper Piston Won’t Compress

Car troubles? Again? There is almost nothing worse than having car trouble. We rely on our vehicles to get us most of the places we need to go and many times we don’t leave time in our schedules for unexpected car trouble.

It’s time to change those brakes. You’ve followed all the steps, but your brake caliper piston simply won’t compress. You need to get your car up and running, you have places to be!

The brakes seem to be on exactly how they are supposed to be and everything appears to be in order. What might be causing the caliper piston to not compress? What can you do to try to resolve the issue?

Brake Caliper Piston Won’t Compress
Brake Caliper Piston Won’t Compress

How Brake Caliper Pistons Work

Brake calipers are one of the most essential parts on your vehicle. If something is not working correctly with the brake calipers, your brakes may fail and you might not be able to stop.

The brake caliper piston applies pressure to the rotor and creates friction that ultimately slows your vehicle and allows you to stop. The brake caliper acts as a clamp on the rotor, fitting over it in a manner that it can compress down against the rotor.

When you initiate your brake system by stepping on the brake, the master cylinder emits brake fluid that forms hydraulic pressure. The hydraulic pressure is applied to one or more brake caliper pistons, which cause the brake pads to clamp against the rotor, slowing the vehicle or eventually stopping it.

Troubleshooting Failure to Compress

The primary cause of brake caliper pistons not compressing when you’ve replaced brake pads or parts is the lack of the right tool. You must compress the piston and turn it clockwise at the same time, which can be a challenge.

The primary key to getting the caliper piston to compress requires you to both compress and turn simultaneously. If you are having trouble compressing, this should be your first goal to try.

If you are having trouble doing these 2 things together, it is a much simpler process if you utilize the right tool to do so. Some auto parts stores will let you check out the needed tool, but it can also be purchased at a reasonable price.

What Are Some Other Reasons my Caliper Piston Won’t Compress?

If you’re quite certain that you are turning and compressing at the same time or you are using the vise or cube tool and still having issues, consider some of these other options.

  1. The piston could be hitting a tough spot. It is possible that your piston is catching on a “tough spot” during compression. You may be able to work through this by clamping it for a short time to apply pressure and then try to run the piston in and out several times to see if it improves.
  2. Check for corrosion. If the piston has any type of buildup or corrosion on it, it could be causing it to not be able to fully compress. The piston may need to be cleaned well or replaced if this is the issue.
  3. Even Pressure. While you are trying to compress the brake caliper piston, be sure you are applying constant even pressure on the entire piston. If the pressure is off balance or not applied to the full area, it could cause the piston not to compress.
  4. Inactive Vehicle. If your compression issue is happening on a vehicle that is not driven on a regular basis, it can cause the pistons to rust or stick. If you are operating a vehicle that you only get out occasionally, you want to check or test the brakes and the pistons before traveling far.
  5. Deformed Piston. Your piston could be slightly misshapen or bent, which would cause the piston to stick and not be able to fully compress. The brake caliper piston could be snagging or catching because of any slight bend or deformity.

What Are Your Best Options to Fix the Caliper Piston Issue?

Brake caliper piston

If you notice a compression issue, whether it is while you are replacing brake parts or while you are driving, you should fix the issue immediately. If your brake caliper pistons are not working properly, it could ultimately lead to brake failure and leave you in a dangerous situation.

Try some of the following recommendations to correct the piston issues.

1.Clean the Pistons

Try cleaning the pistons to remove buildup and corrosion. This would be a simple fix for a caliper piston not compressing correctly and could be your go-to option before spending money to try other fixes.

2.Complete Timely Maintenance

Often, the brake caliper piston could have issues because brake fluid was not refilled and brake pads were not replaced in timely manners. Taking proper care of your brakes could prevent caliper piston issues from forming.

3.Try the special vice tool

You have used your trusty C-clamps for years, but maybe they just aren’t cutting it this time. Try borrowing or using the vice tool that was designed specifically for piston compression use.

If you are using that tool and continue to have issues compressing your pistons, make sure that the tool is fitting your brake parts properly. The tool and pistons can have varying sizes.

Final Thoughts

When you have worked through all of the troubleshooting options you can find and you continue to have issues, it may be time to seek professional help. Mechanics are trained and equipped to take care of these issues and it may be a simple fix (like the tool).

Don’t take the chance of continuing to drive on worn down brakes or brake caliper pistons that you can feel are not compressing properly, give in and call in backup. You were trying to save a buck doing it on your own, but there is no price worth your life or the lives of others who could be impacted if your brakes fail while you’re driving.

We hope you are able to resolve your brake caliper piston compression issue simply and effectively so that you can get back out on the road!

Mike Cross
Life is too short to drive with stock audio

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3 comments on “Brake Caliper Piston Won’t Compress”

  1. I have a 2017 toyota camry with 25k miles on it. my brakes feel a bit" light" . I have to press them in a bit harder than usaul. (fyi when it's cold and I touch brakes they stop on a dime)
    It's not my master cylinder, a leak or low fluid. my rotors are fine. air in the line ?could it possibly be my brake pads with 25 k miles on it??
    Somebody gave me advice that's it's the calipers not touching fully, not brake pads and the person sounded sure of himself.
    I'd like to know a few things before I get this checked out. really wouldnt want to get brake pads if that's not the problem.
    What do you guys think?

  2. Great video..explaining everything in simple language. I feel confident to try a rebuild to a caliper that is stuck in position. Thanks.. I will repost afterwards..

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