Brake caliper rebuilding

[Alex]

I have a pair of brake calipers that require rebuild however I'm unable to get one piston out on each caliper.
In both cases it's the inner piston that won't pop out(with compressed air).
Any suggestions?

No rush as the car is a long way off needing brakes anyway,I just thought I'd investigate  ;D

[StagNL]

I once solved that by rigging up a hydraulic system with a brake master and a large lever.  Took a while but it came out  in the end.

Julian

[TedTaylor]

Push the piston back in and rig something up to stop it being forced back out - though not by bridging across to the piston you want out ...!  I have used a very strong cable tie but anything like this will do - even a suitable clamp

Now when you use the air line you should be able to pop out the other one, and because you have already freed the first piston it can be pulled out with a bit of fiddling.  

If a piston is so heavily stuck in place that air won't do it I use a lever action grease gun and force grease in through the bleed nipple (after unscrewing it!).

MUT

[Glenn]

Hi Alex. I've had a few stinkers like this.  I'd try this - get rid of the dust seal, and then try a good soak of the piston in plusgas or diesel.  I'm guessing you have the better piston back in and secured with a clamp, then give it laldy with compressed air.  Be really careful - can be dangerous when it comes so put some wood in between the pistons so they can't go far.  If that still doesn't work you could try heat, or attack with a cold chisel to get the piston to twist and break the rust bond.  Subtle it ain't!!

[Glenn]

Sorry uncle Ted, you beat me to it!

[Alex]

Thanks everyone!
Glenn I must confess one piston did fly across the garage :-)

[Glenn]

Alex wrote:

Glenn I must confess one piston did fly across the garage

How do you think I know about that!!?  :D

[wealdrise]

Hi,
I am rebuilding a pair of calipers and all four of the pistons had seized.

I split the calipers after sourcing the correct new seal from Canley's.

My solution was to drill a 5mm hole in the centre and then tap an M6 thread(i know our cars are imperial, but I knew the drill/tap size without looking it up and had an M6 bolt to hand :-)).

Using a suitable bolt I then was able to "wind" the pistons out of the caliper body. Just be careful you don't drill into the caliper body and give the whole thing a soak in penetrating fluid for a few days!

I could not find the torque settings for the caliper bolts in my workshop manual, but searching it seems that 40-45ftlbs for the small ones and 70-75ftlbs for the larger ones is right.

BTW I had my calipers ultrasonically cleaned and grit blasted by http://martechengineeringuk.com/ -no affiliation, just had great service from Martin.