Handlebar Master Cylinder Conversion

[moosehead]

I'm assuming Norms bike is the 1980 R100RT he has in his sig line. I believe his current throttle cable control setup on that bike is a dual cable. So the ebay MC throttle assembly he is looking at is a single cable pull version...likely from an 81-84 model.

I had the exact same situation on my 78 R100/7 ...dual cable throttle control. I swapped in in a front end with dual brembo a etc from an 83 RT as well as the handlebar mounted MC from the 83 unit so I just used the set up from the 83 which was a single throttle control + splitter into dual throttle to carbs....easy. Never had any problems with the splitter set up on either my RS,s or RT,s for years. To me a simple solution....or am I missing something????

[loowiloowi]

I just rebuilt my under tank MC. It was badly pitted and I couldn't find a good core to rebuild so I talked to a friend of mine who is a machinist and he bored it out, sleeved it in brass and then honed it for a .005 clearance to the piston. A new rubber parts kit and all is excellent. The brass sleeve cannot be too large on the OD because you need to keep a reasonable amount of the snap ring groove intact. Also lock tite in the sleeve so that brake fluid under pressure can't leak around it. In regards to the bore of the under tank cylinders the parts fitch's show 14mm and 17mm for the ATE pivot type caliper. If you have the $$$ the moto-bins conversion is a great way to go if exact restoration is not a concern..... In regards to the throttle cable scenario the older bikes had 2 cables at the handle bar then BMW went to 1 cable at the handlebar with a splitter to 2 cables under the tank just above the starter vent rubber. Check total length of your cable and find a BMW application that will work with your used conversion handle setup either 1 cable or 2 cables.....

[chasbmw]

Motobins was able to supply me with a twin pull 13mm handlebar MC for my twin disc 90/6. The brakes are now as good as the Brembos on my 82.
The important thing is getting the MC of the right size, 13mm is such an improvement over the 17mm original.

[DucatiPete]

The important thing is getting the MC of the right size, 13mm is such an improvement over the 17mm original.

+1 on that!

My 79 RS had dual cables. The m/c perch I got was off a late 80s RT I believe, so pretty much a straight swap (after shortening the cable lengths a little).

I won't go as far as Chas ("as good as the Brembos") - after all they are only single piston calipers - but I'm pretty happy. Braided hoses help too IMO.

I had great fear and loathing over the original design of (cable to) under tank (and largely forgotten) master cylinder... far too many opportunities for failure IMO.

They are a bitch to bleed though... took mine a couple of weeks (at least) before they settled in. Those ole ATEs are probably as good as they'll ever be now...

[Chuey]

I have found the cable splitter to be a reliable part. I have three bikes with that system. No problems so far.

Chuey

[SteveD]

They are a bitch to bleed though... took mine a couple of weeks (at least) before they settled in. Those ole ATEs are probably as good as they'll ever be now...

Steve in Orange (ex Dubbo) had a way to bleed that system, which involved undoing it from the frame and tilting it in the correct direction...or something like that. It might be worth asking he or Mal?