Caliper Piston Won’t Compress - Common Causes (& What To Do)

Whether you are running into trouble changing your car’s brakes or the vehicle is pulling to one side and wearing through brake pads, you might be dealing with a caliper piston that won’t compress. How can this be resolved?

When the caliper piston won’t compress, it’s likely due to a rusty or corroded caliper piston, caused by a bad piston boot. If it’s the rear caliper piston, consider the chance that the incorrect wind back procedure is being used. 

In this guide, we look closer at what’s causing the seized caliper pistons. You will also learn how to reduce the problematic caliper piston. We also examine how much it costs to replace a seized piston. 

Caliper Piston Cases Seized

1. Corrosion

Most often, the reason the caliper is not moving is because the caliper's piston has become rusty due to damage to the caliper boot. Brake calipers can’t operate properly if corrosion or rust is involved. The caliper pistons' ability to compress can be affected by any level of corrosion.

If you are using your vehicle regularly, this probably won’t happen to you. If the boot gets damaged, it can cause corrosion. 

RELATED: Brake Caliper Sticking (Causes & How to Prevent it)

2. Worn boots or seals

As time passes, piston seals can wear. The piston may become stuck if the seals fail. 

The rubber boot that covers the piston keeps it lubricated and protects it from damage. The rubber boot can tear or become damaged and water will seep into the piston, causing it to seize. 

3. Broken Brake Hose

Problems with the brake caliper's hose are common. Brake fluid can flow onto the piston if the hose begins to crack or break. Because it can’t get back to the master cylinder where it belongs, the caliper is going to stick.

However, there are times when the caliper itself isn’t actually stuck. Sometimes, the brakes will feel the same as before the hose is broken. To find the source of the problem, do a thorough inspection.

4. The Windback Procedure is incorrect

If the problem occurs with the rear caliper, it’s possible that you aren’t following the guidelines of the service procedure. Rear calipers work differently to the front. To get the rear calipers compressed, you must follow certain steps.

You can’t simply push rear calipers back in. The rear calipers must be turned at the same moment and then pushed. To operate the rear brake pistons, you can use a windback tool. 

A diagnostic tool may be needed to reset an electric parking brake.

RELATED : How to Change Brake pads with an Electric Parking brake

How to Complement Stuck Caliper Pistons

1. C-Clamp

Place the C-clamp above the caliper, and towards the end of your piston. There’s a screw on top that must be adjusted correctly. Wood is recommended to protect the surface of your piston from any damage. 

By turning the screw the pressure will increase, which allows for the piston's compression. Keep this tightening until you get the piston compressed exactly where it is needed. 

2. Channel Locks

Channel locks can be used in the same way as the C-clamp. Place the channel locks behind the brake pad and one side behind the caliper. Place the brake pad and caliper between your grips.

To compress the piston, squeeze the channel lock together. Start slowly and gradually increase pressure as necessary. 

Related: Signs that your brakes are failing

3. Piston Compression Tool

Your job will be much easier if your tool can work with the pistons. You must ensure that your compressor is correctly adjusted to the task. You don’t want to have the push bar hanging out.

The caliper compressor should be placed alongside the pad. While the pushbar applies pressure on the brake pad, pump the compressor tool. This should cause the brake pad to press into the piston, allowing it to retract. 

4. Screwdriver

You often don’t need any fancy tools to compress a caliper piston. Your standard screwdriver may be sufficient to complete the task. 

Place your screwdriver in the window of the caliper. As you insert the screwdriver into the openings, be sure to hold on tightly. The screwdriver must dip until there’s an equal amount of balance of force. You should pull the brake piston back by pulling.

Once the screwdriver has been seated, you should pull in slightly. The pressure should be applied in an outward direction. Your screwdriver can be placed between the brake pad and piston. You should now be able push the piston back gently. 

Caliper Seized Caliper Repair Costs

You might be able to get your caliper down with one of our tips. Every situation is unique. It could actually be the brake line causing similar symptoms. In this case, your caliper piston might be functioning properly.

If you have to replace the brake pedal caliper you will need to pay between $250 and $500. While the parts are priced between $100-300, labor can run anywhere from $150-200. Cost depends on what vehicle you have and the labor rate in your area. You can save money if you replace your brake caliper yourself. However, the bulk of the cost is borne by the component itself. 

You can sometimes restore the caliper with a new piston and seals, but it’s often cheaper and easier to buy a new caliper instead.