Brake caliper rebuild
How to rescue those seized brake calipers by fitting new seals and pistons.
In some cases, a sticking piston inside a brake caliper can be freed off by spraying penetrating fluid down inside the dust cover and around the walls of the piston. This can only be done with the caliper removed, but you won’t need to detach the flexi-hose. You may have to carefully press the brake pedal to push the piston out a little, but not too much.
Once the piston has been lubricated with penetrating fluid, it will need to be pushed back in again to help the penetrating fluid work and to see if the piston has become easier to move (check the brake fluid level in the reservoir before doing this). Use a G-clamp to force the piston in. You may need a flat piece of metal to spread the load across the end of the piston.
Some pistons cannot be pushed in, but have to be wound in instead. A brake caliper windback tool should be used here, although some people have used long nosed pliers, but there is a risk of slipping and stabbing your hand. Once the piston has been retracted, carefully press the brake pedal to see if it moves out – but not too much as it may pop out entirely.
The pistons in the rear calipers on the Mazda MX-5 and some Volvos have a stop fitted in the back to help with handbrake adjustment. If this is wound in too far, then you may think the piston has seized and you won’t be able to refit the caliper, especially with new discs and pads fitted. Instead, wind the stop out for more clearance.