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How to unseize a brake caliper

How to unseize a brake caliper

Having a brake issue and think that one or more of your calipers could be seized? Read on to find out how you can diagnose it, and what you need to do next – and find more practical advice at the bottom of the page…

What are the symptoms of a seized brake caliper?

Brakes seized after sitting? When brakes seize it can be because the piston becomes stuck within the caliper, the pads become stuck to the disc, or on single-piston calipers the slide pins can seize.

If the brakes seize when the vehicle has been unused then the symptoms are fairly obvious: you can't get the car to move.

Check out more FREE advice for the DIY mechanic with our Home Mechanic Guides

If it's the piston that's stuck within the caliper the car could well feel down on power (as its fighting against the resistance of the brakes). You may also get uneven braking, with the car pulling to one side. As you drive, the binding brake will get hot – very hot, and you'll quickly smell the brake linings overheating, and even see the smoke coming from them. It's a distinctive acrid smell. If this occurs, stop! If you carry on driving not only could the heat cause the brakes to catch on fire, but you will also damage the discs and potentially damage any component connected to the wheel hub.

If it's the slide pins that have seized then the car may appear to drive normally, but the pads will only be pushed onto the disc from the piston side. This will give reduced braking ability, plus wear out the pad on the inside much faster.

Often this is only picked up at MoT test time when the brakes are tested and are discovered to be imbalanced. 

Find out how to change your car's front brake pads and rear brake pads

What are the symptoms of a seized brake caliper?

What causes brakes to seize on?

The main cause of brakes seizing is inactivity. If a vehicle is sitting for a long period of time, especially out in the open, it's not uncommon for the brakes to seize. This is usually a case of the pads becoming 'stuck' to the disc as it becomes coated in surface rust, particularly after rain.

Also bear in mind that brakes are subject to a huge range of temperatures, they're permanently exposed to the elements, and are never serviced between pad changes. As a result corrosion can build up in key areas and failure occurs.

If it's the rear brakes that are causing problems it may not be the caliper. Sometimes it's the handbrake mechanism that's causing the brakes to remain on. This could be a seized handbrake cable, the mechanism itself could be corroded and seized, or the electronic handbrake could be faulty.

Check out the Haynes YouTube channel, with hundreds of model-specific procedures such as this…

Should you rebuild or replace a brake caliper?

Even if you free off a sticking caliper there is a high likelihood of it seizing again if it's caused by the piston or slide pins. You could find yourself having to repeatedly dismantle the caliper, when it would be more sensible to either rebuild it or replace it entirely.

A rebuild kit is something a competent DIYer can do at home, but it is a bit involved, and you do need to be careful. But as long as the corrosion on the various components isn't too bad, it's worth considering.

You may want to get a secondhand caliper and rebuild that with new seals but don't just buy a used caliper and fit it – you've no idea about the condition of it, and it could even be worse than the one you're replacing. Haynes recommends buying a brand new caliper - it's the wisest option.

How to unseize a brake caliper