Master Cylinder Piston Rubbers

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johnbirchjar
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Master Cylinder Piston Rubbers

Post by johnbirchjar » Tue Apr 24, 2018 7:39 pm

Hi guys,having fitted the new Front Brake Master Cylinder Piston Rubbers I am not getting any reaction when operating the Brake leaver,which leads me to think I have not put them on the Piston correctly evil, please advise the correct positioning(silly old me failed to notice which way round they were on the old one red face)rgds,J.B.

BlackIP2
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Re: Master Cylinder Piston Rubbers

Post by BlackIP2 » Tue Apr 24, 2018 8:09 pm

Not sure about the seals being the wrong way around, but I've just drained and refilled my front brake system after a cosmetic overhaul, and the same thing happened.
I had to bleed the system several times and then the old trick of leaving the brake lever pulled back against the handlebar overnight with a strong elastic band bought the pressure back.
Might be worth trying that before stripping down the master cylinder again?

johnbirchjar
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Re: Master Cylinder Piston Rubbers

Post by johnbirchjar » Tue Apr 24, 2018 11:17 pm

It's a thought,but I am not even able to bleed the system exclaim,this is what makes me think it's the Rubbers that are the prob,and neither the w/shop manual for the IP2 or the parts book for the Classic are any use 'cos both of them show pic's of the round reservoir while mine is the "coffin" shape,I await further information from fellow club members wink,J.B.

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Richard Negus
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Re: Master Cylinder Piston Rubbers

Post by Richard Negus » Wed Apr 25, 2018 8:44 am

JB,
I've just done one.
The seals look similar but are not the same. The primary seal has small slots moulded into the diameter.
2018-04-25 082400.jpg
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Anthony Duffield
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Re: Master Cylinder Piston Rubbers

Post by Anthony Duffield » Wed Apr 25, 2018 9:59 am

John,

Once you are happy that the seal kit is the correct one and correctly fitted, the following details how I eventually bled the air from my master cylinder as fitted to my Commander.

Last year when overhauling the calipers even though on completion I had used a new oil feeder filled with brake fluid and pumped fluid back up to the master cylinder it still took me a very long time to get the master cylinder to prime.

This year I renewed all of the brake hoses and again had issues bleeding the master cylinder until I tried the following:

With the old master cylinder to junction block hose temporally connected to the master cylinder with the loose end in a container filled with new brake fluid I primed the master cylinder, tied the brake lever hard against the handlebar reconnected the new hose and with a couple of pumps of the brake lever primed the system and bled the calipers.

The above worked for me and having kept my old hose will use the same method the next time I have to bleed the front brakes.

Hope this helps.

Tony

johnbirchjar
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Re: Master Cylinder Piston Rubbers

Post by johnbirchjar » Wed Apr 25, 2018 11:27 pm

Hi Richard,the sketch was exactly what I was looking for,many thanks Very Happy.
(I tried to print it off but could not on enlargement evil),so would you mind e-mailing it to me so's I can print it off and put it in the w/shop manual?(please nicely)
Tony,your "Bleeding System" seemed a bit too complicated for this old biker,so what I did was,(as the reservoir was off the bike wink)Fill up the reservoir,screw to top back on,fill up the piston chamber(after the piston assembly was in place)screw the pipe union(plus the pipe of course) back into the reservoir,then bleed the brake pipe where it goes into the junction for the two front calipers,bleed the front brakes,and "Hey Presto" they seem to work just fine cool,I shall do a test run in the near future and report anon.once again,thanks guys,ride safe,J.B.

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