Boxerworks.com

To all at Ken's who helped me walk through the stiff pressure on the front disk on the R65, I copied and pasted the below.

I checked the casting underneath the master cylinder on there and it is the "16" not the "13", ergo the stiffness at the lever.

Thanks again, I'll go on the hunt for another one.

Doug


"A 1” master cylinder creates 127.4 PSI as compared to a 7/8” master cylinder which is 166.7 PSI based on your foot making 100 pounds of force at the master cylinder. It is important to consider that the smaller cylinder makes more pressure but the smaller bore will move less fluid. More travel will be needed to make up for the reduction in fluid moved by a 7/8” master cylinder as compared to the larger 1”.

Glad to hear you've got it resolved, Doug.

Sounds like the 16mm master cylinder would be perfect for dual disks--unless you already have dual disks, that is.


Ken

Yeah, I asked that question from the seller, he said it was a single set up like mine. Who knows, I'll start looking at the various resources for a good used one with the "13 " stamped on the underside of the part.


Grrrrrrr

Thanks for a great time Ken.

Not sure what year R65 we are talking about but the single disc 78 -80 models with the Twin piston ATE calipers had a 13mm master cylinder as stock. That's the set up I have. It gives a firm lever but you need a strong grip to get decent braking. I can only imagine a 16mm would be terrible.

81 on R65's with the Brembo caliper came down to a 12mm master cylinder even though the caliper pistons are the same size as the Ate's.

I think BMW were being too cautious when they specified a 13mm on the earlier bikes. They must have been worried that we were going to lock the wheel ! If I was changing a master cylinder I would opt for the 12mm every time.

Here is one option, if you want to change from under the tank to a handlebar mount master. I have bought from this seller pretty often in then past years, he is constantly getting BMW parts from salvaged machines.

http://www.ebay.com/itm/BMW-motorcycle- ... 35c7bf0851

+1 on dealing with lamontsanfurd (Larry Chabira) I've always gotten great deals on well described parts from him, and he offers a return policy.

I've got a 13mm MC from an 83 RT that I was going to use on another bike to convert it from under tank MC to handlebar MC. Was going to run SS brake line directly from handlebar MC to the single disc ATE...

Think it will work? Curious as to what kind of "feel" I'll have at the lever? Hmmm....guess we can always give it a whirl. Will be interesting.

Hoping it works, as the under tank MC is pouched and leaked everywhere (what a mess) and this was an alternative fix that I looked forward to. SS brake line was from my old GS and think will fit fine.

"I've got a 13mm MC from an 83 RT that I was going to use on another bike to convert it from under tank MC to handlebar MC. Was going to run SS brake line directly from handlebar MC to the single disc ATE...

Think it will work? Curious as to what kind of "feel" I'll have at the lever? Hmmm....guess we can always give it a whirl. Will be interesting.

Hoping it works, as the under tank MC is pouched and leaked everywhere (what a mess) and this was an alternative fix that I looked forward to. SS brake line was from my old GS and think will fit fine."


I have a handlebar mounted 13mm MC on a single disc R90/6 and it works great. I used an R80ST brake line with no problems mounted on R90S bars.

I have a handlebar mounted 13mm MC on a single disc R90/6 and it works great. I used an R80ST brake line with no problems mounted on R90S bars

.

Well that's good to hear...thanks. Hoping to get at it in a few weeks to make the conversion and give it a go.

moosehead wrote:

I have a handlebar mounted 13mm MC on a single disc R90/6 and it works great. I used an R80ST brake line with no problems mounted on R90S bars

.

Well that's good to hear...thanks. Hoping to get at it in a few weeks to make the conversion and give it a go.

I thought it was a 13mm, but it's actually a 12mm off an R65 that I modified to run dual throttle cables. Sorry to misinform you.