Master cylinder piston stuck.

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maz
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Master cylinder piston stuck.

#1 Post by maz » Wed Apr 29, 2020 8:28 pm

Hi, master cylinder piston stuck/seized fully in bore?, does not look corroded, I had a leaking front brake line and I think the seals dried out. sorry stick with me before you switch off, this is on a magura master cylinder on my old 1996 r850 which I have had stored for about 4 years. Seal kit comes with a new piston so as compressed air did not work or heating the cylinder I thought I would drill and tap the piston and pull it out, extreme measures but I,m hoping to rescue the master cylinder as replacements are ridiculously expensive.
Anyway, anybody tried this before? any advice?
Cheers mike.

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BikerGran
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Re: Master cylinder piston stuck.

#2 Post by BikerGran » Wed Apr 29, 2020 9:54 pm

My first thought is, can you get a replacement piston?
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maz
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Re: Master cylinder piston stuck.

#3 Post by maz » Thu Apr 30, 2020 8:12 pm

New piston comes with the replacement seals fitted in a kit with a new seal/bellows for the reservoir and some silicon grease all for the princely sum of £52ish.

RiceBurner
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Re: Master cylinder piston stuck.

#4 Post by RiceBurner » Fri May 01, 2020 2:28 pm

take the banjo bolt off the other end and knock it out with a suitable drift.

Just be careful not to mark the inside of the cylinder.

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Re: Master cylinder piston stuck.

#5 Post by fatboy » Fri May 01, 2020 4:13 pm

Good advice from Rice burner,
If you can drift the piston from either end of the bore then hopefully it will free up the ' stiction ', failing that leave the bloody thing in a jar soaking in fluid for as long as possible
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mangocrazy
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Re: Master cylinder piston stuck.

#6 Post by mangocrazy » Fri May 01, 2020 6:53 pm

If the piston is rusted to the bore, then immersing the whole lot in a citric acid solution may work. Citric is brilliant stuff for eating rust. The hotter the solution, the faster it works. I put small parts for de-rusting in my cheapo ultrasonic bath in a citric solution. The rust fairly melts away.

maz
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Re: Master cylinder piston stuck.

#7 Post by maz » Thu May 14, 2020 8:09 pm

Interesting idea with the citric acid, I would have tried that. Drilled and tapped the piston, its only aluminium and sacrificial as the kit comes with a new piston and seals. the piston actually twisted in the bore when using the tap I probably could have pulled it out like a cork. Used a bolt as a puller. Bore all good cleaned out all the debris fitted kit and bled the brakes really easy much easier than the rear. Very happy all seems good.
Fitted new battery, bike started first turn very impressed I don't think I've run the bike for at least 2 years.

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Gio
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Re: Master cylinder piston stuck.

#8 Post by Gio » Fri May 15, 2020 8:40 am

maz wrote:
Thu May 14, 2020 8:09 pm
I don't think I've run the bike for at least 2 years.
Beware the rubber then, might have gone hard.
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