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How to compress a brake piston on the caliper

Several cars which I have worked on - a Honda, an Acura, and an Audi had rear brake pistons which needed to be screwed in to be compressed after a brake pad change.

Problem is (especially if you do not have even a basic repair manual) that old pistons will not screw in.

This method is only for pistons which must be SCREWED in to be compressed - they will usually have a large "plus" in the middle, or in case of the Audi, two notches across from each other for pliers.

If you have an old caliper which is completely stuck (it does not rotate when you are absolutely POSITIVE that it must be rotated to be compressed) you might need to use a pipe wrench to get it to rotate. Be very careful to not twist the brake line - secure the caliper very well when putting force trying to unscrew it!

For pistons which do rotate freely, but do not retract (compress) - do this test. Turn then a little counter clock wise. If the piston retracts then you are doing the right thing. In many cases, it will extend when rotated counter clockwise, but not compress when rotated clockwise.

If you do not have access to (and cannot rent from your car parts store) a special piston retraction tool, a C clamp or similar can be used.

Place the C clamp on, make sure to secure it at the back of the piston, and place the clamp at the center of the piston. Tighten it somewhat, but not too hard. Piston will not retract by you putting force on it. Now get adjustable pliers, and being careful to not catch and damage the rubber boot, grab the piston and rotate it with pliers clockwise, while compressing the clamp at the same time. Piston should not retract. Refer to the following pictures:

Notice the tube in the background to relieve the brake fluid pressure.

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