The New And Improved Unofficial R65 Forum V2

Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: weasel01 on May 25, 2009, 12:59:04 PM

Title: Square Master cylinder leak?
Post by: weasel01 on May 25, 2009, 12:59:04 PM

With the Fork seal job behind me,Thanks again!

I've moved on to my leaky front brake master cylinder.
I have the replacement piston kit but
I'm having trouble taking it apart?
I have removed the handle,removed 2 Allen screws that are underneath
threaded into the handle block,removed the 3 top screws and 1 bottom screw from the reservoir and dont see anything else but it is solidly in place?
I cant even remove the reservoir tank?
Is there another hidden circlip or something else or am I just being too cautious?

Title: Re: Square Master cylinder leak?
Post by: Bob_Roller on May 25, 2009, 01:06:47 PM

You've got all of the fasteners removed, now all that is holding you up is corrosion .

You need to tap out the master cylinder with a drift or punch.

It would be a good idea to cover everything up with old towels, and plastic trash bags, in case it gets messy from old brake fluid .

The only thing holding the reservoir on is an o-ring, try twisting the reservoir by hand to get it broke loose .

Title: Re: Square Master cylinder leak?
Post by: weasel01 on May 25, 2009, 01:28:14 PM

Bob, you are obviously THE MAN!

corrosion was it,it all came apart but felt like it was epoxied together.

It's full of crud
Should I pull it loose from the hose?
If so is there a torque value to retighten the hose?


It's my first time in on this machine and I'm in a "learn as you go phase"  sorry if I'm asking stupid questions.

Title: Re: Square Master cylinder leak?
Post by: Bob_Roller on May 25, 2009, 01:36:01 PM

It's better to ask, than to go ahead blindly, that route can get expensive .

Don't apologize for asking questions, all of us here have been where you are at, and thoroughly understand your situation .

It may make it easier to remove the line , to remove the innards to the master cylinder off of the bike, put into a vise with a couple of pieces of wood to hold the master cylinder .

Title: Re: Square Master cylinder leak?
Post by: weasel01 on May 25, 2009, 03:30:49 PM

Ok got it all torn down cleaned all the goo out and now I'm set to reassemble but I noticed the new kit has a large washer and an extra
rubber piece that wasnt on the one i took off?
also with the "extra" rubber piece there is no room for the snap ring that holds it all in?

Title: Re: Square Master cylinder leak?
Post by: Bob_Roller on May 25, 2009, 03:38:51 PM

I'm looking at my original master cylinder that I removed about 19 years ago, and I have the same pieces.

My best guess is to install the master cylinder tighten up the two bolts, and then place the washer on the 'stem' from the master cylinder, then the stepped rubber part, I think it's just a dust cover, to keep debris out of the area .

Title: Re: Square Master cylinder leak?
Post by: weasel01 on May 25, 2009, 04:33:01 PM

Thanks again Bob!
got it all back together added fluid and to my surprise I have a leak free (so far) front brake!!!

Title: Re: Square Master cylinder leak?
Post by: bruce_launceston on May 25, 2009, 07:14:11 PM

I had the 2 washers left over and thought they were extra but then I found them in the lever mount, as Bob said it is the dust seal.
Have a look at the lever side of things and you should find the old ones tucked away in there.
Cheers Bruce

Title: Re: Square Master cylinder leak?
Post by: bruce_launceston on May 25, 2009, 07:22:09 PM

Also if you have all that corrosion and crap in there you may need to hone out the master cylinder. I have done this twice on this mastercylinger without any problems.
Get a short length of 1/2" wooden dowell and cut a slot in it lengthways but only half way through. Tuck the end of a piece of 2000 grit wet and dry in the slot and wrap the paper around the dowel. You can spin this around by hand to clean up the inside of the m/c. Use a fine oil or WD40 or similar and dont leave any longitudinal hone marks in the cylinder and with any luck it will live to brake again!

Cheers Bruce

Title: Re: Square Master cylinder leak?
Post by: nhmaf on May 25, 2009, 07:54:07 PM

Hmm, when I put my rebuild kit in mine I had a problem with that extra large washer and rubber boot - no matter how I tried it seemed that the rubber boot bound up the piston so that it wouldn't work smoothly.  Not sure if I still have those parts or not..

Title: Re: Square Master cylinder leak?
Post by: Justin B. on May 25, 2009, 08:54:15 PM

I put some silicone lube on the piston shaft and it's been fine...

Title: Re: Square Master cylinder leak?
Post by: weasel01 on May 26, 2009, 07:37:11 AM

When i cleaned the handle bar mount I found the same metal washer smahed and burried up in the mount so I put the piston in the cylinder after I cleaned it out (didnt see any scratches) installed the snap ring
mounted the MC back on the handlebar mount and simply slid the "extra" rubber piece on the handle side of the mount and everything seems right....I think.

Title: Re: Square Master cylinder leak?
Post by: Justin B. on May 26, 2009, 02:23:30 PM

I believe it's supposed to go on the master cylinder side, but I can't remember off-hand.