Relocate MC (Master Cylinder) to Under Triple Tree??

[andyleonard]

Cafe project needs MC out from under custom tank and owner doesn't want MC on the bars. Has anyone simply remounted the under-tank MC assembly to a new location under the triple tree? There's room, hoses/cables reach, any downside? Anyone have a pic of a bracket?

 

[akbeemer]

I believe you'll need to provide more detailed information about the bike and what it is you are trying to accomplish in order to get a helpful response.

Welcome to the forum.

 

[lee]

Welcome to the forum.
Your thread title is hard to understand
I'm guessing MC is master cylinder?

 

[20774]

I'm guessing MC is master cylinder?

Yes, with a hydraulic front brake showing up for the '74 models, the master cylinder for the single disk front brake was located under the tank. The tank had a spot formed into the bottom to accept the master cylinder bolted to the upper spine of the frame. I think they felt that under the tank was less dangerous in the event of an "off" when riding. Of course, it meant more difficulty in checking levels of fluid as well as they sometimes sprung a leak and made a mess. Beginning maybe 1981?? they moved the master cylinder to the topside of the right handlebar.

 

[andyleonard]

Yes, yes and yes. Thank you. I forgot I am appearing as a newbie. I haven't been active with Airheads for a long while but have been riding and wrenching Airheads since I climbed aboard my 1968 R69S in 1969. I traded it in in 1978 for an R100RS, which I have owned since, just recently passing it on to my brother. So 1969 to 2022 with those 2 bikes. I'll see if I can recover my old logins.

The brake project is as stated. The fellow has a rat R80 that someone chopped into a "cafe" bike and abandoned. It runs, but that's about it. He's purchased a shiny new (shoddy) Indian-made black BMW tank he likes and has fitted it to his bike by removing the Master Cylinder (MC) and reservoir from underneath. Yes, he knows about the handlebar conversion. No, that's not an option for him. This is a rat, project bike. Please forget "how it's supposed to be."

What I'm looking for is clues from someone who has remounted the MC under the triple tree and used all the original connections and hoses/cables. I can cobble something up but it would be lovely to see how the last guy did it. No new parts, just a new location. Thanks.

 

[kinterridge]

I remember seeing, years ago, a R100 that was semi customized, that had the factory master cylinder and it was mounted on a fabricated bracket/shelf that was mounted to the voltage regulator bracket and the opposing relay bracket and I think if I recall the oem lines were able to be utilized. This was up in Ephrata, PA at the older Blackman's BMW, so many years ago.

 

[20774]

Wow. Taking the MC under the tank and moving it to the bars? First I don't think the hoses will be long enough. Second the original MC mounts to the upper frame member which has a much larger diameter than the handlebars. So, that's not going to work quite so well. Plus the original MC is fugly to put on the bars. And it's not going to work upside down if that's what you were thinking. You'd need to create some kind of perch or rest for the MC to be mounted to. All that hanging down from the bars is going to takes lots of room and compromise the ability to turn the bars...likely it will run into the tank on right-hand turns.

 

[andyleonard]

NBWTFOWYATTEWATU&UAs




(Translation;

NO BODY want to figure out what you are trying to express with all those useless & undefined abbreviations

English bitte,

then glad to hep if I can

Thanks for the reply but if you don't know what a cafe bike conversion is and you've never seen MC in technical writing as an abbreviation, then I'm afraid you won't be ale to help.

 

[andyleonard]

Wow. Taking the MC under the tank and moving it to the bars? First I don't think the hoses will be long enough. Second the original MC mounts to the upper frame member which has a much larger diameter than the handlebars. So, that's not going to work quite so well. Plus the original MC is fugly to put on the bars. And it's not going to work upside down if that's what you were thinking. You'd need to create some kind of perch or rest for the MC to be mounted to. All that hanging down from the bars is going to takes lots of room and compromise the ability to turn the bars...likely it will run into the tank on right-hand turns.

No thanks. Not on the bars, under the triple tree.

 

[PoorUB]

Thanks for the reply but if you don't know what a cafe bike conversion is and you've never seen MC in technical writing as an abbreviation, then I'm afraid you won't be ale to help.

Not to bust your balls, but there were a few here that were not sure of what a MC was. I assumed master cylinder.

When writing it is best to use full words at first, then abbreviate afterwords.

Sorry, I can't help much on your MC (Hammer?), project. But you can mount the MC where ever you want as long as you can get the controls hooked up and functioning and also get hoses to fit. Obviously mounting it else where will require custom brake line(s).

What did they do? Run a cable from the lever to the MC to work it??

 

[20774]

No thanks. Not on the bars, under the triple tree.

Most of my comments still apply I think for under the triple tree. Not to mention that space gets compromised when the front end dives. Not really a good spot I think.

For those that have MCs under the tank, mid to late Airheads, this was pretty obvious as to the general question. At least it was to me!! But yeah, spelling things out in detail along with year/model of bike always helps out!

 

[andyleonard]

I remember seeing, years ago, a R100 that was semi customized, that had the factory master cylinder and it was mounted on a fabricated bracket/shelf that was mounted to the voltage regulator bracket and the opposing relay bracket and I think if I recall the oem lines were able to be utilized. This was up in Ephrata, PA at the older Blackman's BMW, so many years ago.

OK, here we go. I just had a quick look yesterday but there's an ear welded to one of the 2 horizontal frame braces just under the steering head. A bracket bolted there could hold the master cylinder and utilize the original cable to the lever and the hose to the caliper. Has anyone made such a bracket?

 

[andyleonard]

Not to bust your balls, but there were a few here that were not sure of what a MC was. I assumed master cylinder.

When writing it is best to use full words at first, then abbreviate afterwords.

Sorry, I can't help much on your MC (Hammer?), project. But you can mount the MC where ever you want as long as you can get the controls hooked up and functioning and also get hoses to fit. Obviously mounting it else where will require custom brake line(s).

What did they do? Run a cable from the lever to the MC to work it??

MC Hammer....I get it.

The old under-tank master cylinders (pre-81?) used a mechanical cable from the lever to the cylinder under the tank, then a hydraulic hose to carry the juice down to the caliper on the single disc.

It looks to me as if mounting it under the triple tree will allow use of both original cable and original hose. I'm just looking for a bracket design and comments.

 

[melville]

I just took a stroll out to my shop, where my /6 is sitting with the tank off and I have a spare MC that I could hold up to different spots and I think your best option would be to somehow mount it to the top of the motor, above the diode board. I'd offset it to one side to make access to the reservoir easier.

The aesthetic issue with that is that the MC is no longer hidden and would be an opaque item in the frame. Cafe racers need lots of light passing through them.

Mounting would be the curious bit. The stock MC is so clearly designed to mount to the top of a tube with a hose clamp I'm not sure how you'd redesign the mounting system. If you could figure that out, you'd likely need custom cable and hose, with the cable longer and the hose shorter.

I'm curious to see what you come up with.

 

[PGlaves]

I am sure most of the posters know this but that system was BMW's original anti-lock brake system. The brakes were marginal on their best day.

 

[20774]

Thanks, Paul! Actually the more original anti-lock brake system would be drum brakes. I'll take my single disk ATE over my R69S drum brake anyday!

 

[andyleonard]

I just took a stroll out to my shop, where my /6 is sitting with the tank off and I have a spare MC that I could hold up to different spots and I think your best option would be to somehow mount it to the top of the motor, above the diode board. I'd offset it to one side to make access to the reservoir easier.

The aesthetic issue with that is that the MC is no longer hidden and would be an opaque item in the frame. Cafe racers need lots of light passing through them.

Mounting would be the curious bit. The stock MC is so clearly designed to mount to the top of a tube with a hose clamp I'm not sure how you'd redesign the mounting system. If you could figure that out, you'd likely need custom cable and hose, with the cable longer and the hose shorter.

I'm curious to see what you come up with.

Terrific reply. Thank you. Agreed it needs to be offset right to account for a shorter cable and a longer hose. I believe the aesthetics here are a moot point until everything lives again. Form is following function very closely here. Fortunately this bike has tiny bars so maybe....

 

[kinterridge]

Wow. Taking the MC under the tank and moving it to the bars? First I don't think the hoses will be long enough. Second the original MC mounts to the upper frame member which has a much larger diameter than the handlebars. So, that's not going to work quite so well. Plus the original MC is fugly to put on the bars. And it's not going to work upside down if that's what you were thinking. You'd need to create some kind of perch or rest for the MC to be mounted to. All that hanging down from the bars is going to takes lots of room and compromise the ability to turn the bars...likely it will run into the tank on right-hand turns.

No, not the bars, under the frame tube under where it was factory mounted, but above the starter cover. A custom bracket was fabricated and it wass mounted to the 2 relay brackets that are factory welded the the frame tube. not upside down either tube. The relays were mounted elsewhere. Sorry for the confusion.

 

[PGlaves]

When I first read, "Relocate MC to Under Tree" I thought the OP had found a new place to park a motorcycle under a tree. Silly me!

 

[mikegalbicka]

When I first read, "Relocate MC to Under Tree" I thought the OP had found a new place to park a motorcycle under a tree. Silly me!

You're not the only one? Figured it was a Christmas present.