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