R65 front master cylinder bore?

[darrylri]

I didn't get this bike new; in fact a friend is the original owner, and he gave me the bike a year ago.  I don't know the complete history of it, but he told me that the MC had been replaced by his local dealer, quite a long time ago.  

I noticed the brake lever situation right away, as we were pushing the bike to load it into my pickup.  I asked Jim what was up with the brakes.  He thought it was completely normal; certainly, that's the way he had been riding it for a long time.  (The bike came to me with 169,000 miles on it!)  He didn't think it was odd, even in comparison to his current bike, an F650 single.

[Bob_Roller]

I think Julio A. made a posting a few months ago about a later K series four piston caliper that had the same bolt hole pitch as the R65 caliper .

That would be an interesting upgrade to say the least !!!!!!!!!!

[Julio A.]

Those calipers fit right into the mounts on the R65's Forks but does not clear the rims if it is aligned with the disk. But when I made it fit and it cleared the wheels, there was no way to have the disk go into it.

Now I have a pair of four pot brembo calipers w/ brackets, an extra ATE and brembo left caliper(excluding the one currently installed on the R65), a spare right brembo caliper that only fits the R100, and a brand new spare disk that I recently found out came from a different and incompatible airhead.

I also have a ridiculous quantity of spare brembo pads but no ATE ones. So when I wear out my current ATE pads I will be replacing the whole caliper with my spare Brembo caliper.  

All of which is collecting dust on my cabinet....
They make a good display piece though.

Haha, there were a lot of attempts to convert the thing to a dual disk.
Everything failed miserably.  

[Blackjack]

OK, area of a circle is Pi R², so for a 16mm master cylinder that 64Pi, ignore the Pi.

For a 15mm its 56.25Pi, again ignore the Pi.

64 divided by 56.25 gives you 1.1377777777.

So for a given amount of travel a 15mm piston displaces around 13.7777% less fluid than a 16mm one.

So unless there was something else amiss, the difference in travel would be a little under 14% greater, for the same pressure at the pads.

[Bob_Roller]

You can modify the pads for the Brembo calipers to work on the ATE calipers, you just need to remove material from the steel back plate .

About 20 minutes work on each pad .

[tvrla]

I didn't get this bike new; in fact a friend is the original owner, and he gave me the bike a year ago.  I don't know the complete history of it, but he told me that the MC had been replaced by his local dealer, quite a long time ago.  

I noticed the brake lever situation right away, as we were pushing the bike to load it into my pickup.  I asked Jim what was up with the brakes.  He thought it was completely normal; certainly, that's the way he had been riding it for a long time.  (The bike came to me with 169,000 miles on it!)  He didn't think it was odd, even in comparison to his current bike, an F650 single.

Hi Darryl!

I'm the guy who stayed at your place when you were gone to the autumn beemer bash this last fall! I was going to stop again on my way back from Los Angeles but ran out of time. Hope to make it to your tech day this spring.

Anyway, just wanted you to know the hot ticket is a 14mm master for the dual discs. I've even heard the 13 works very well, but haven't tried it yet. If you're having problems with the 15mm coming most of the way back to the bar, there's something wrong. Since it's already got stainless lines, it's got to be something with the caliper or master.

You got me!

But I do know the 14 works very well for me and I'm really happy with the results on several of my beemers. My understanding is that from the mid seventies into the 80s, hydraulic brakes were still a new thing on BMWs and the engineers still hadn't gotten the ratios right. Going to the 14mm with the dual two-pot Brembos gives great feel and control and none of that wooden feeling.

Terry

[Blackjack]

Back in the 70's, disc brakes were not only a recent thing, tyres were made out of far more "excitibg" rubber compounds, and more critically, every one was used to drum brakes along with the higher lever effort that comes with them.

The difference in swept volume between a 15mm and a 16mm means that the 15mm cylinder's lever will travel about 1.13777 times  the distance of the 16mm one to displace the same amount of fluid. This of course assumes that the 16mm and 15mm cylinders have the same lever ratio.