This bike uses a single ATE 38 mm caliper (as in the size of the piston inside the caliper, not the size of the caliper shell). In 1976 the ATE caliper was changed to a 40 mm model to improve braking. There was also a change to the master cylinder mounting system resulting in a single hole in the brake fluid reservoir that mounts on top of the master cylinder. Other than these small changes, the work I did applies to all the /5, /6 and /7 models of the ATE caliper and under-the-tank master cylinder.
You can read about how to do this work here:
I had occasion to work on both my 1975 R75/6 and someone else’s 1976 R75/6 at the same time, so there are some pictures of the markings on the 40 mm caliper and the different mounting systems (two hole and one hole) of the brake fluid reservoir.
Some pictures from this write-up are below.
Master Cylinder & Fluid Reservoir Mount Under Gas Tank. Note the Evidence of Brake Fluid Leak.
Earlier Style Master Cylinder Fluid Reservoir-Two Holes With Mounting Bracket
Later Style Master Cylinder Reservoir-Single Hole With Threaded Sleeve
Earler Two Hole Master Cylinder
Master Cylinder Piston Assembly Removed
Removing Top Hat From Master Cylinder Piston
Master Cylinder Rebuild Kit Parts
New Master Cylinder Piston with New Rubber Seals Installed
Master Cylinder Installed on Frame Tube
R75/6 Caliper Seal Kit – Source: MAX BMW
Front Face of Piston with Center Hole Surrounded by Rubber Dust Seal
A Blast of Compressed Air Removes Piston
Dust Seal Installed in Large Groove in Piston
Pulling O-ring On Eccentric Pin With Pick
Movable Pad with Flat Face of Pad Pointing to the Front
Fixed Pad Secure with Wire Clip
Caliper With Painted Metal Line Installed
crystal clear ! thanks
Really nice job!
Thanks for sharing the info!
BR
Britt,
You’re welcome. And, I haven’t made the decision yet on the the tank bra on the 1977 R100RS I picked up. If I do get rid of it I’ll let you know.
Best.
Brook.
Piston on my 1976 R75/6 is completely frozen. Soaked, air blast, hydraulic press,
nothing works. Any lead on where to find a used caliper?
Hi Dexter,
I’m sorry to hear this one is really rusted tight.
eBay is a good place to find these. I’ve had good luck at Duncan’s Beemers who has an eBay store
[http://stores.ebay.com/Duncans-Beemers]
Larry Stonestreet at Stoner’s Beemer Stash is also a source for used parts. He does not have a web site to my knowledge.
[[email protected]; 951-813-1704].
And a general ebay search should also yield some results.
Best of success on overcoming this.
Best.
Brook.
Hello Brook,
I have used this post as well as many others during servicing of my ’76 R75/6. I recently removed the excentric pin of one of the calipers, and noticed there is also an rubber o-ring which sits in the fork slider ( the top of the excentric pin slides in there). It’s completely crumbled, and prevents smooth rotation of the pin.
I can’t find a part number anywhere, do you perhaps know about this o-ring and it’s part number?
I hope my question is somewhat clear, greetings from the Netherlands!
René
Rene,
I believe it’s part# (34 11 1 237 303) which is for the 40 mm caliper.
I hope this helps.
Best.
Brook.
Brook,
I thank you for sharing your wealth of knowledge.
I have a 1975 R75/6. Should I lubricate the eccentric pin in the brake caliper? I just rebuilt the master cylinder and caliper. I was thinking caliper slide grease. I cannot seem to find any mention of a need to lubricate this pin.
Another thing I noticed is that there are threads cut into the brake lever but the brake cable “adjuster” has no threads. I have to back the cable adjuster on the master cylinder almost all the way out to minimize the free play. I spoke with Rusty at Max BMW Portsmouth who mentioned something about the master cylinder lever contacting the threaded adjuster.
I am putting an adjuster on the hand lever where I believe it was originally intended. I will make sure that the most of the free play is taken up by the master cylinder cable end adjuster.
Peter,
I lubricate the eccentric pin with brake grease.
Best.
Brook.