Getting Those Brake Caliper Pistons Out
- Gerry Masterman

As of:  16 April  2006 

        From time to time, I hear stories about how hard it is to rebuild MGB front calipers.  I've done it many times and never felt it was all that big of a job.  The biggest problem seems to be removing the pistons from the calipers.  If you've tried compressed air through the hydraulic line opening and been unsuccessful, here's a last ditch method.

        I've done this several times.  However, I have to say up front that I ALWAYS replace the pistons with new ones every time I rebuild a set of calipers.  Chances are good that, if your calipers are unwilling to give up their pistons, the pistons are bad anyway.  So, losing the stuck pistons isn't much of a loss.

First thing: I always split the caliper halves.  Its a real pain trying to do anything with them if they are still together.  I carefully drill a hole through the center of the offending piston, making great effort not to drill through the caliper behind it.  I use a #7 drill bit, which leaves proper size hole to thread with a 1/4X20TPI tap

Once the hole is drilled, carefully tap the hole with the 1/4 tap.  After the hole is tapped, then you can screw a proper sized bolt into the hole until it hits the backside of the caliper.  As you screw the bolt in the piston, the piston will be pressed out the front side.  You will likely have to find a bolt that has threads all the way to the head to get the piston all the way out.  The size of the hole and bolt is strictly up to you, but 1/4X20 has always worked just fine for me.  Once the piston is out, rebuilding the caliper is pretty straight forward.  Keep in mind that the inside of the cylinder bore does not have to be smooth, because the actual sealing surface is on the piston, which will be new.

Now, after all of this, I have to say this: I've found that most of the time, it is more cost efficient to just buy  newly rebuilt calipers for the local discount parts house.  I seldom do this, however.  I am hardheaded and refuse to be beat by a simple job like rebuilding brake calipers.  But, on the other hand, if you do not have the facilities to do the job, then you will be much better off buying  rebuilt.