The New And Improved Unofficial R65 Forum V2

Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Semper Gumby on January 13, 2009, 07:05:39 PM

Title: Brake Caliper/Master cylinder information
Post by: Semper Gumby on January 13, 2009, 07:05:39 PM

I was trolling around for drum brake stuff on this web site and found an excellent discussion on caliper piston to master cylinder ratio.  I think this will help answer questions about what master cylinder you should get.

http://www.vintagebrake.com/mastercylinder.htm

Does anybody know the width of our ATE/Brembo Caliper pistons???

TTFN,

Title: Re: Brake Caliper/Master cylinder information
Post by: rl900 on January 14, 2009, 07:12:09 AM

The F08 Brembos are 38mm (X2), I believe the ATE's are the same, but not positive.
Ron L

Title: Re: Brake Caliper/Master cylinder information
Post by: MrRiden on January 14, 2009, 05:50:11 PM

The standard "bore" for the R65 with single disc is 12mm the LS with dual disc has a 15mm for the "Master". Justin had actually made up some caliper pistons if I remember correctly. He probably could answer that for you. A quick check of MotoBins shows pistons for ATE and Brembo calipers but alas no dimensions given

Title: Re: Brake Caliper/Master cylinder information
Post by: Justin B. on January 14, 2009, 05:59:53 PM

I briefly looked for my piston sketch today while I was out in the shop and couldn't find it.

Title: Re: Brake Caliper/Master cylinder information
Post by: drewboid on January 15, 2009, 11:22:28 AM

The old pivoting ATE (/6 vintage) was 40mm single piston and used a 17mm mastercylinder.
Standard for the R65 was a 12mm master and 38mm dual pistons
R65LS with two front disks used a 15mm master and two 38mm calipers (total of 4 pistons)

The R65s are within the recommended ranges
My dual disk R65 still has the 12mm master but it uses most of the lever travel to fully engage - on the other hand I can get a lot of braking with relatively little hand strength.

According the table my /6 should feel like a toggle switch; however the front wheel is 19" and there is a cable to operate the master cylinder. It feels fine to me - sometime soon I will be adding a second disk to it also and seeing if I need to change the master cylinder as well.
YMMV -

Title: Re: Brake Caliper/Master cylinder information
Post by: nhmaf on January 15, 2009, 09:26:44 PM

I can attest that my LS with 15mm m/c is fairly "wooden" in feel and rather "binary" in operation - it isn't the recommended way to brake but I find that if I use more than 1, or at most, 2 fingers it gets hard to modulate the stopping power without performing a stoppy.  This wasn't as much an issue with the rubber brake line, but with the braided stainless I have on there, it is "enhanced"

Title: Re: Brake Caliper/Master cylinder information
Post by: Lucky_Lou on January 18, 2009, 05:06:30 PM

My 1980 r65 is a twin disc and has a 16mm mastercylinder the size is stamped underneath search realoem with the frame number and it tells you what should be fitted
Lou

Title: Re: Brake Caliper/Master cylinder information
Post by: not-so-fast-ed on January 18, 2009, 06:59:26 PM

My '87 has a 14mm master, single caliper Brembo - twin 48mm pistons.

Rebuilt the caliper, but only flushed the cylinder & replaced the reservoir, cap, and "o" ring seal.

Seems to work well.

Title: Re: Brake Caliper/Master cylinder information
Post by: rl900 on January 19, 2009, 09:29:45 AM

"My '87 has a 14mm master, single caliper Brembo - twin 48mm pistons. "

 :-? Ooops! I guess the Brembos on R65's must be F09's not F08's like I thought.  Mine has ATE's.