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Discussion Starter #1
Hi all: My 81 MHR has a stuck rear Brembo piston; it's about 14mm out but doesn't want to move any more. Tomorrow its off to the tool shop to get a long 2mm diameter drift to try and knock it out further. Would heat help? Any words of wisdom would be most appreciated.
 

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Easy to fix. Get an air hose, the tyre filling type, with a small nozzle, take out the bleed nipple and blow air into the caliper.

WARNING Wrap the whole thing in a rag or similar and keep your fingers out of the way. Sometimes it will come out like a bullet and I'm sure many can tell a tale about getting nipped by the ejecting piston.

To install - clean out thoroughly, including the piston or buy new ones - smear a tiny bit of rubber grease on the seals and reinsert. I've done it numerous times and never had a problem.
 

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Thanks Eldert I misread the lack of words and got excited at the thought of sending a caliper piston across the workshop.

Air will probably push it out as well but I'd say it's either the washer, the seal or corrosion holding it in. If you haven't already I'd flood it with WD40 or something similar and wait.
 

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Discussion Starter #6
Apologies for the lack of clarity; it was late when I wrote! Yes, rear master cylinder is being a problem. After soaking it in penetrating fluid, I put the lever back on and managed to push the piston back and forwards and now the spring is powerful enough to move the piston by itself (most of the time). Drawings are pathetic and none of my literature explains how to disassemble the thing. On another forum, I've been told to simply get a longer drift and hit harder. My guess is that the last seal, closest to the lever is a big fat one that needs extra force to let the piston out.

On topic, I did use compressed air, very carefully, with rags and eye protection to pop the caliper pistons out last night. Even with the precautions, they pop out very fast and very suddenly and there's old brake fluid behind them. For anyone that hasn't done this before, I advise putting some rag between the pistons as well as around the whole caliper when blowing. The piston closest to the air popped first. I then broke the caliper, sealed the communicating fluid hole with two small pieces of electrical tape, put the caliper back together and then carefully blew out the other piston. Going to clean-up my old P08 Goldline rear caliper halves tonight!

Thanks to all for your input. I know I will need more so keep an eye open for my troubles!

I have to say that having a living room and kitchen full of Ducati bits is so much fun; just like the old days.
 

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Ooops forgot about that eye protection!

Bloody things fly out don't they? I got the tip of my finger caught about 30 years ago so always made sure after that. And I tell you it didn't tickle.
 

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I have always just pumped them out naturally by topping off the master cylinder and pumping the lever till the piston pops out.

Much safer, no air pressure launching the piston or fluid spraying everywhere.
 

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Discussion Starter #9
Thanks Bob: In my case, the rear master cylinder is jammed so would not pump. Also, as was in my case, the caliper pistons were not jammed but just good and tight in their seals. As noted above, the piston closest to where the pressure was input popped out first. One one has popped out, the other will not move unless the caliper is broken in two and the interconnecting port is plugged so that all the pressure is applied behind the remaining piston.
 

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Discussion Starter #10
I just got the piston out of the rear master cylinder using a long, small screwdriver. As expected, there's a tightly fitting seal at lever end that has to be broken free to allow the piston out. I could feel a ring of something on the inside of the bore that I could not remove with rags wrapped around a large screwdriver so I put a dab of Solvol on my pinky and very lightly rubbed the ring to see if I could remove it. My finger was black; a good sign. I then use a rag and the bore is now really smooth.
 
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