Leaking Master Cylinder

[lynnsabcs]

The master cylinder on my 80 R65 is leaking at the base of the resevoir. Is the resevoir available separately or do I have to buy a complete master cylinder?

Lynn
Knoxville, Tn

[airhead]

Is the MC round or square? If the round one, to my knowledge it is not replaceable and it means a new MC. If square, then you can replace the reservoir, but more likely it could be just an O ring that needs replacing.

Bill......................;-)

[Justin B.]

The stock 1980 is a round one so he's probably out of luck...  I have never looked at ours that closely, but surely something could be done if one was determined enough...

[nhmaf]

I have heard of (1) instance of someone with a leaking round MC being able to pry it out
of the metal base, and carefully line the inside edges with an epoxy and get the thing to
seat right again and seal, but most that I have heard who tried this didn't fare well.
Some folks look for a later model airhead that someone is parting out and convert to
the square/rectangular unit, which is rebuildable / repairable in case of future leaks.
Of course, this requires buying more parts - I don't know if the switch from the perch
for the round MC will fit in the MC perch for the rectangular...

[Rob Valdez 79 R65]

I would imagine switching from the round m/c perch to the rectangular would involve such things as converting the throttle cable from a dual cable (early) to a single cable at the throttle, to a splitter and two short cables to the carbs.

I think it is a worthwhile swap, simply because I could then bolt on a couple of black G/S brush guards easily.
But the throttle cable set-up is not necessarily better.

On the bottom of the perch, cast in, is the piston diameter.  My round one is 13mm.  It is for a single disk set-up.  If you do get a different m/c, you will want to shop for the same size to prevent any problems.

[Bob_Roller]

If one were to keep the bike for some years to come, I think the swap over to the rectangular master cylinder would be to your advantage, as the parts for the later version, are more readily available, than the round set-up. I'm sure parts availability will get to be a problem in the not so distant future, as the oldest R65's are coming up on 30 years old !

[lynnsabcs]

Since the master cylinder was more weeping than a leak, I thought I would try an experiment. I drained the fluid and removed the round master cylinder assembly including hand brake. I cleaned the cylinder well with brake fluid and let it dry.

I turned the cylinder on it's side and ran a thin bead of clear epoxy around the edge between the metal base and the nylon cylinder making sure the inside edge between the 2 was filled with epoxy. Flipped it over and did the other side. I let it dry overnight.

Refilled the next evening and bled the brake. That was about a week ago and so far everything is dry and the "repair" doesn't look that bad.

Lynnsabcs
Knoxville

[Rob Valdez 79 R65]

At first I thought you meant inside is where you put the epoxy.

But you put it on the outside?  And it is holding!  Not bad!  [smiley=thumbup.gif]

[chris_79R65]

My master cylinder has been weeping for quite some time.  I'm finally buying a new one, the older round model for my 79' R65.  They are pricey though!  Not interested in dealing with the rectangular conversion.  If the round one has lasted almost 20 years so I figure the new one will last another 30.

chris 79R65

[Rob Valdez 79 R65]

Hi Chris!  Good to hear from you again!  Glad you are still around.

You should ride down to Frankfort, KY in a few weeks for the Beemers in the Bluegrass rally.  I am going to try my darndest to be there.

Rob

[Bob_Roller]

My master cylinder has been weeping for quite some time.  I'm finally buying a new one, the older round model for my 79' R65.  They are pricey though!  Not interested in dealing with the rectangular conversion.  If the round one has lasted almost 20 years so I figure the new one will last another 30.

chris 79R65

The only problem that I would have with buying a new master cylinder, is that it was probably assembled in the early '80's, so the chances of the piston seal rubber being 25 years old is a distinct possibility.

[dewjantim]

Try Re-psycle BMW, they probably have a used one.......Dew.

[TomHoldom]

Hello all
I have a the same leak with my 1978 R65 which I'm getting on the road again after 10 years or so, but with the additional problem the 2 out of 3 of my reservoir cap screws have sheered and just turn without coming out.....
Is my only option here to drill out? 4mm diameter (sorry in metric france)

[Barry]

The screws are threaded into brass inserts pressed into the nylon body of the reservoir and the inserts are probably spinning around. They may spin when you try to drill out the screws but it's worth a try.

[TomHoldom]

not quite thought that through....the heads are obviously just spinning. Cap should just lift off, but it doesn't want to..?