Brake Caliper Repair...

Well, I tried a method to get the stuck inside piston out of the caliper.
I drilled a hole in the center of the backside, then used a drift and bench vise to press on the piston.
The piston moved after some pressure and revealed the flaking chrome plating that was probably the cause of the jam.

It took a bit of work to clear the corrosion and chrome but finally was able to press the piston all the way through the outside bore and out.

I tapped the hole in the caliper with a 5/16" x 18 thread and will use a socket set screw to seal the hole.
Perhaps a better choice of thread/sealing is recommended?

This is a spare caliper I used to try this method, but I would like to put new seals and pistons in and see if the plug holds pressure.

A 1/8 NPT plug would have been a better choice, regarding sealing. It will hold pressure fine.

Thanks for the advice.
I'll get the 11/32" drill bit for the tap hole and try it.

Hello Bob,

I would be tempted to use a set bolt with a copper washer plus sealant on thread. I would not use a grub screw

Had you tried the grease gun method? Added heat after that? Before drilling?

I did try compressed air and also hooking the caliper up on a bike with a good master cylinder and the hydraulic pressure would not move the piston.

I'm wondering if many operational bikes have unequal brake pad pressure applies on the disc due to sticking pistons.
I have seen examples where the piston did not release pressure when braking is off.
Quick and unequal wear to the pads.

concours said:

A 1/8 NPT plug would have been a better choice, regarding sealing. It will hold pressure fine.

Click to expand...

agree. It ought to be a tapered thread. Suggest getting a professional to do this job properly.

Only the concurs inspectors will notice the back side plug which for some decades has always worked with plain straight threaded hole to skip the Rub Goldberg set ups. Always put in SS pucks for the next guy to praise you over. Inspect bores closely after the chrome and rust flakes dragged across. On Trixie I didn't want to alter the factory finish so had holes taped in the pucks and they both came right out as the tap was withdrawn. Oh yes I gave it a good normal shot at em by heating and pounding on wood with a stack of big super magnets on for inertia mass prior to easy way out.

I think a sticking piston is quite a common , and often unnoticed problem.

I have worked on high pressure hydraulic systems. The pumps often had multiple outlet options. Put the fitting in the one you need and a bung in those you don't. As long as the thread is sealed correctly, it will be fine - there is no magic in a taper thread, they can still leak and even worse cause cracks if over tightened, especially in situations not designed for them, .
Were I worked we used a gloopy Rocol product which was called RAS on the shop floor. Can't remember the full title. Filled gaps and then set sufficiently to make it hard to get out.
No doubt there are more modern sealants these days.

Or would getting it welded be an option? Don't know the material spec of Norton calipers.

A copper washer works well on mine. The hole was drill back in the mists of time an has 8mm domed cap head.

Personally I would avoid thread sealant as brake fluid an it may react over time and as with elsewhere in the system a copper washer should be all that is needed.

I would also recommend that you pay close attention to the clearance between the blanking screw head an the wheel spokes. Perhaps I trail fit of repaired caliper may be useful to check as my spokes only miss the screw head by 1/32".