Stuck piston removal

[acealfa]

Hi all,

I started stripping down a pair of old calipers but I’m faced with a stuck piston that won’t budge no matter what I try. Usually they come out with a couple of pry bars under the lips but this one is jammed solid & they just slip eventually. Does anyone have at tips or tools to remove it? I’ll be forever grateful 😅

[LimSlip]

The proper tool for this job is a pair of "reverse" vice grips with semi-circular ends that grip inside the center of the piston. However these often fail on badly stuck pistons IME.

You might be lucky enough to find a rawlbolt (used for hanging heavy things from concrete/brick walls) of a suitable size to grip the inside of the piston, or make up a simple metal sleeve to increase the diameter of a smaller rawlbolt. A slide hammer attached to the other end would be useful.

[acealfa]

I was looking at this but doesn’t show instructions but looks similar principle

https://www.24mx.co.uk/motocross-accessories/tools...

[Chris32345]

Air line into the fluid inlet/flexihose connection and force it out like you would if using the brakes

[Evoluzione]

Put it back on the car, stop all other pistons and push that out with the brake pedal.

[acealfa]

A bit awkward with them being 4 pots but I guess I could just take the half & put the other piston back in then clamp it in the vice.

Thanks for the ideas

[LimSlip]

Chris32345 said:

Air line into the fluid inlet/flexihose connection and force it out like you would if using the brakes

Pointless with a stuck piston, an air line only provides a small fraction of the brakes hydraulic system pressure.

[Chris32345]

LimSlip said:

Pointless with a stuck piston, an air line only provides a small fraction of the brakes hydraulic system pressure.

Pointless trying to remove it then because it will still provide for more pressure then you ever could by hand

[GreenV8S]

Evoluzione said:

Put it back on the car, stop all other pistons and push that out with the brake pedal.

^^^^ That.

[acealfa]

Air pressure didn’t move it so next step grease gun but cartridge is empty so need to order one. These are spare calipers so unfortunately don’t have the car to use.

[GreenV8S]

If you don't mind getting a bit creative with clamps and so on, you could pair the stuck piston up with a free one and use a clamp on the good piston to blow the stuck one out.

[Piersman2]

GreenV8S said:

If you don't mind getting a bit creative with clamps and so on, you could pair the stuck piston up with a free one and use a clamp on the good piston to blow the stuck one out.

This sounds like the best suggestion so far.

Pull out the other piston(s), fill calliper with fluid, seal filler, then apply clamping force to push other piston(s) back in. I'd use my 6t bearing press for starters, and then the bush pullers if I needed more 'press' force. It's gotta go eventually!

The only thing that can move is the stuck piston!

Like it.

Edited by Piersman2 on Sunday 27th September 23:34

[acealfa]

That is a very clever idea. I will try it

[LimSlip]

Chris32345 said:

Pointless trying to remove it then because it will still provide for more pressure then you ever could by hand

Pointless trying to remove a stuck piston? Maybe you could clarify your argument as it makes no sense at all.

[tapkaJohnD]

Fill the hollow of the piston with ice and keep it renewed while you heat the body of the caliper.
You could use a freeze spray on the piston instead. Available for sore joints or to freeze pipes.
If the body will thermally expand while the pistons stays cool, it might loosen.

What penetrating lubricants have you tried?
For bolts, rubbing a candle onto them while they are hot has worked for me. The liquid wax wicks (!) down the threads, or in this case between piston and caliper.
OR, less folkwise, i'm impressed by Innotec Deblock: https://www.ebay.co.uk/itm/Innotec-Deblock-XS-Oil-...

John

[stevieturbo]

Weld something to the piston and DIY a slide hammer or puller.

[the cueball]

acealfa said:

I was looking at this but doesn’t show instructions but looks similar principle

https://www.24mx.co.uk/motocross-accessories/tools...

I use a similar kit when rebuilding my calipers for both cars and bikes.

Never failed to remove any piston, stuck in or not.

Great piece of kit.

[rustednut]

Just a thought.

If the piston is that seized, what will the bore be like? Will it take a new piston or clean up ok, or does it render the caliper of little/no use?

Probably not worth the expense and/or effort to remove a really seized piston anyway if so ?

Or maybe send it to reconditioning people who may be able to overhaul it to better standard?

Edited to add

never used them, but a company like bigred ? or others are available.

[LimSlip]

rustednut said:

Just a thought.

If the piston is that seized, what will the bore be like? Will it take a new piston or clean up ok, or does it render the caliper of little/no use?

Minor pitting in the bore is not an issue. The seal sits in a groove in the bore and slides against the piston so the surface of the piston is the important area for sealing.

[SuperPav]

Whenever I had a piston that was SERIOUSLY stuck, and which I was going to replace (usually necessary if it's stuck that bad), the method is to drill a hole in the middle of it, tap it out to take a thread (e.g. M8), and then just screw a bolt in it, giving it taps as you go along. The bigger diameter the bolt you can use the better as it reduces the pressure on the inside of the caliper where it makes contact.