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Suggestions for freeing frozen Brembo pistons

Posted: Sat Feb 18, 2006 5:16 pm
by Peter Tourin
Can anyone give me some helpful hints for freeing up frozen calipers? I soaked my 2 calipers with PB Blaster for a week, clamped a rubber hose to the brake line and hit them with 120 PSI -- no luck. I heated the outside of one caliper with a torch to see if I could heat shock the piston loose -- again, no luck. Can anyone suggest a tool for grabbing the pistons from the inside so I can try to rotate them and free them up? Or anything else I should try?

Thanks - Peter Tourin

be free

Posted: Sat Feb 18, 2006 10:14 pm
by BevHevSteve

seperate the caliper halves, get a socket that fits down inside the piston, remove the bleed screw now whack the piston IN to free it.

Now pry the piston OUT using 2 small screw drivers, 180 degrees away f rom eachother........

Hopefully you didn;t melt the rubber and kill your caliper..............

Posted: Sun Feb 19, 2006 5:32 am
by Peter Tourin
> Hopefully you didn;t melt the rubber and kill your caliper.............. <

Well, tell me I haven't trashed anything yet....

The only rubber I see is an o-ring between the caliper halves and the seal on each side around the piston. The seals are very old and dirty, and I pulled them before doing anything. I'm assuming I pull the pistons, clean the cylinders as necessary, then put in new pistons and replace the seals. I'm not missing anything here, am I?

I'll give it a try this afternoon and see if it gets me moving.

Thanks - Peter


Posted: Sun Feb 19, 2006 8:09 am
by BevHevSteve
Hi Peter, there are also seals around the piston down in the piston bore - 1 seal per piston. They are a square cross section seal, about 3mm, and are down in the bore about 1 cm or there abouts [I am not looking at one so can;t say for sure]. This is the seal that is going to be a pain to remove once youi get the pistons out - and you will - you MUST get every bit of rubber out of the groove or the new seals will leak............

Posted: Sun Feb 19, 2006 10:45 am
by Peter Tourin
Thanks, good to know. I'll start pounding the caliper I didn't heat first, and see how it goes. - Pete

Posted: Sun Feb 19, 2006 7:47 pm
by DesmoDog
Here's a fun fact that my dad taught me - some grease guns use the same thread on their tips as a brake line, so you can simply remove the gun's tip, screw the caliper onto the gun, and use that to force the pistons out.

I've used a grease gun on a few stuck brakes, works pretty well most of the time. I don't like using air - with air, when things let go it can get quite exciting, not to mention brake fluid can go everywhere. With grease, it's a slow process, no flying pistons to worry about. A bit of a mess though...

I seem to remember that on my GT I had to attach a hose to the caliper and then screw that onto the grease gun though... but that may have been when i was trying to take the M/C apart?

Posted: Sun Feb 19, 2006 8:55 pm
by Peter Tourin
I'll check my gun and see if it likes vintage Italian brakes....

Posted: Tue Feb 21, 2006 3:23 pm
by Geoff
I was advised to cook the caliper halves in the oven at 400 deg F and then, holding them piston-out in an old oven glove, whack them twenty times on a block of wood. Then pistons slowly made their way out but my hands hurt like hell! Seals didn't melt and came out ok. Suggest really cleaning the calipers first though as the dirt on them made the calipers go a bit brown after cooking.

Grease gun sounds good!

Re: Suggestions for freeing frozen Brembo pistons

Posted: Thu Mar 01, 2012 3:13 pm
by in-two
Hey guys,
I know it's 6 years since the last post , but I've just spent an energetic afternoon dealing with this problem. My '75 ss has lain untouched for 18 years under a tarp, BUT, I had to push back the pads/pistons to wheel it about the garage back in the day. Now,on getting to grips with restoring the irreplaceable FO8 shaved calipers, I had the following issues. No amount of air (15 bar) would shift the pistons, the pistons were fully retracted, so the usually very effective 'push in' technique failed and my Wanner grease gun ruptured!!! as nearly did I.
Luckily I had sets of spanking new Brembo pistons, seals etc to hand so a destructive technique was an option. It turned out that two types of corrosion were causing the problem, the original pistons were ferrous (steel?) and either a yellowish chrome or nickel plated, and had started to erupt with rust spots in the caliper bore, secondly, and I think worse, was some kind of reaction in the seal groove with the alloy of the caliper which grew a white oxide(?) layer that pushed the seal against the piston so hard that only brute force was the answer. With the calipers separated and thoroughly soaked in penetrating fluid, I had managed to free one piston by gripping the external diameter with a pipe wrench and twisting it, a few degrees at a time, then blowing by air, brutal but effective. The others just laughed. Working on the twisting technique, and running out of options, I cut two 5 mm grooves at 180 degrees in the protruding edges of the piston with a cut off air grinder, rammed a bit of 5 x 50 mm bar stock in the two slots and pushed to and fro and blew with the air gun in the bleed nipple hole, blocking both the inlet port and the joining port.
Bang! out came the piston as if it always wanted to escape!
On cleaning up the caliper bores and seal groove there seemed to be minimal damage, and the new seals and aluminium alloy pistons slipped in nicely. I have yet to pressure test, but so far, so good.
I appreciate that, in a better equipped workshop, some kind of hydraulic pump set up might have been more effective, and that I didn't try heat, which would usually scare anything from anything, but I really didn't want to damage the caliper castings.
Happy to supply more detail/photos if anybody is interested, and particularly to hear of any better/less brutal approaches.

Re: Suggestions for freeing frozen Brembo pistons

Posted: Sat Feb 15, 2014 3:27 am
by dukabmw
I have just had the same problem with original steel/chrome pistons seized on the rear brake.

I could not budge them by soaking them in Penetrene, nor gripping the edge of the piston with vise grips, then attempting to turn the piston in the bore with an adjustable spanner on the vise grips.

Air in my air compressor would not budge them either, so I took them to a workshop where the mechanic also tried to blow them out with 140 PSI air pressure with no luck.

Last attempt was to use the grease extraction method, but was reluctant, as you have to remove all traces of grease before installing new seals/pistons etc....
I went to an auto spares shop, and found 2 grease nipples (as I have the dual bleed calipers), and screwed them in. I also got the original bolt that holds the brake line on and found a 2 washers and thick oversize nut that fitted over the bolt easliy. I sandwiched the oversize nut between the washers then put them over the bolt, and inserted the bolt into the supply line.

I got a piece of thick steel to slip into the caliper housing where the rotor disc sits, to prevent one piston popping all the way out, and therefore possibly stop the other piston coming out. :vroom: :-D

I then pumped grease into the grease into the grease nipples, and after much time and effort, they slowly started to come out. They both came out to the steel plate, which was then clamped tight in the housing, so I undone both bolts holding the housing together and clamped the vise grips onto the pistons and turned them to which they finally worked their way out.

It was then a hassle cleaning all the grease out of the supply holes drilled into the caliper.

Re: Suggestions for freeing frozen Brembo pistons

Posted: Sat Feb 22, 2014 6:23 pm
by abmartin
I've had success moving the pistons by removing a brake pad and pumping the brake lever while the caliper is still mounted on the fork with the wheel and brake in place. You can place a shim between the piston and the brake disk so that the piston doesn't pop out all the way. Repeat the procedure for the other side of the caliper. Once the pistons have moved substantially they are relatively easy to pull out the rest of the way with a suitable tool, after removing the caliper from the fork and splitting it.