Removing rear master Brembo piston - need help

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81mhr900ss
Diana
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Removing rear master Brembo piston - need help

Post by 81mhr900ss » Mon Nov 26, 2018 10:21 pm

Hi all: I'm pulling my 81 MHR apart for an overhaul. I took the rear brakes apart today; the master cylinder piston has been jammed for years (bike's been off the road 28 years). The only parts I cannot remove is the master piston and the plastic cup! I have a flat head punch that was just the right size to start the job but it''s not long enough to finish it and I think the thing is jammed. It's sticking out about 17mm so far. Any words of advice? I'll be at the tool shop tomorrow to find something longer but the hole through which to work is only about 2.5mm. Do you think heat will help?

As for the plastic cup, it will not budge and I don't want to ruing it as it is great condition. Maybe I'll just have to clean around it.

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Craig in France
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Re: Removing rear master Brembo piston - need help

Post by Craig in France » Tue Nov 27, 2018 4:15 am

For the piston in the m/c, time, patience, plenty of penetrating fluid (of which ever particular mix you prefer: acetone cut with atf isn't all bad ...), a drift that is long enuf (a blunted 3" or 4" nail normally does the job) and repeated sharp blows with a light hammer. And a bit of heat never hurts, of course.

For the plastic cup - care. If it will break if forced. Do you really HAVE to remove it?

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81mhr900ss
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Re: Removing rear master Brembo piston - need help

Post by 81mhr900ss » Tue Nov 27, 2018 4:15 pm

Thanks Craig: I managed to get the piston moving back and forwards under its own spring pressure (sometimes) last night and left it soaking in penetrating fluid. Got to find a bigger drift! I decided to leave the cup as-is and clean around it. What is it that hold the thing in place? Just an extra fat seal? The drawings don't show it. I'll be doing the front brakes later this week; I did a front Brembo many years ago and don't remember knocking out the piston to be so difficult.

I have to share; it's been so much fun pulling the old bike apart in my living room and kitchen; just like the old days. I found a few surprises; HT leads are glued in to the coils?!?, I found the unused side-stand leads, using compressed air to push out the brake pistons works great, everything is dirtier than expected, stuff I thought would be really tight wasn't and vice-versa. Scraped a few knuckles. More fun/frustration every day.

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Re: Removing rear master Brembo piston - need help

Post by BevHevSteve » Tue Nov 27, 2018 8:21 pm

Hi there - you just need a longer drift and pound that sucker out of there. Easy. Regarding the cup it is threaded on thats all. Use a band clamp to remove it if you must but really there isn't any reason to remove it unless you want to replace it (yes I have new cup kits availavle for both your rear and front Brembo master cylinders).
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