Stuck caliper pistons, what will definitely free them?

[DaveEdge]

I'm refurbing some 4 pot front calipers...

2 are free on 1 and 1 is free on the other, meaning 5 are seized...

I've tried compressed air 100psi... Still not budging.

I've read about air/manual grease guns but I've also been through the ball ache of mangling together a brake fluid (hand) pump that also did absolutely nothing to free them and I'm reluctant to fill the calipers full of grease for no gain tbh... but if someone tells me it will free the worst stuck thing then I might consider buying an air gun tomorrow.

Just to confirm, I'm trying to get them out not compress them, they'll all compress for some reason.

Any ideas lads before I try my next idea of seeing if they'll loosen by throwing them through my window?

Cheers

[mgbgt stop]

try putting them in a bucket of diesel overnight to free up all the crud thats makingthem stick.I use a foot pump 2/3 pump and they usually pop out if that doesnt work try a little heat around the pistons

[Good Scrap]

Best way is using hydraulic pressure from a spare master cylinder, clamp the ones that are moving with steel straps and bolts , or wedges between opposite ones that move, otherwise your effort is being used just moving them, and not affecting the seized ones.

The smaller the master cylinder bore the better as you can develop higher pressure, but move less fluid

Compressed air is actually quite dangerous as once thay start moving they can fly due to the rapid expansion of the air.

Brian

[optimusprime]

I've done some by heating them in the oven for an hour.
That freed them off.

Just do not,i repeat, do not,get caught by the missus ......

[DaveEdge]

Cheers lads

I'm replacing all rubber seals so I'll try some heat.

Yeah I know airs abit dangerous but I made sure they couldn't fly anywhere with a piece of wood clamped between Brian, ran out of ideas and heard people had success.

Don't any of you recommend grease guns then?

[DaveEdge]

Btw I did originally try a footpump after soaking them in penetration fluid and still didn't budge them.

Thanks for the suggestions though.

[composimmonite]

I boil callipers in water. That way they get 100 degrees of heat without risk of overheating as with blowlamp.

[optimusprime]

That's why i used the oven method, you get an overall heat, rather than a localised heat build up from a blowtorch.

[DaveEdge]

Will definitely do boil or oven bake them tomorrow evening, if that fails I'll try a grease gun.

Cheers

[nomad]

Not had this problem on a car but on a bike with a pair 4-pots :
leave 1 caliper in place - remove the other caliper but leave all hoses connected.
wedge something between 2 of the pistons to lock them.
use pedal - hyraulics will push out one of the "unlocked" pistons.
clean / polish / refit that piston with new seals.
Then *just* repeat for the other 7

Heat sounds best, I avoid air as I'd expect it to blow free at high speed

[reliantreviver]

Have used the grease gun method to good effect in the past, hydraulic pressure is safer / more progressive. I guess it all depends on how good you grease gun is really!

[DaveEdge]

Update lads.

Tried soaking them in boiling water, no change, these weren't budging...

Ended up getting an air grease gun, couldn't use brake system as it has different fitting. FWIW these can push out upto 6000 psi of pressure!

Hose connection is same as the gun's! Pumped it through and they came straight out, well I've had to muck about putting the loose ones back in because they come out too soon, which was a pain as apart from being really messy I only have one clamp that will fit so had to keep on compressing them one by one until they all reached the piece of wood in the middle.

Now just need to clean up the mess from inside the calipers.

Cheers for the advice and suggestions