I picked this bike up in April 2016. Finally, on September 1, I got started on it. I had to finish up work on the 1975 R75/6 “S” update and completed that in July. I’ve put about 600 miles on that bike and its running well. You can see all the work I’ve done on the R75/6 here:
I made a short video to show the routing I used and where the front turn signal, neutral switch, voltage regulator, starter relay, coils, Dyna III electronic ignition, oil pressure switch, neutral switch and rear tail light/turn signal wires go.
It includes links to two other write-ups: The first describes the wiring connections to the diode board, alternator, points, and starter motor when I replaced the timing chain; The second write-up shows the details about the circuit board connection areas inside the headlight shell and how to connect the right handlebar switch inside the headlight shell.
I had to replace this switch and decided to document “what wire goes where” inside the headlight shell on the circuit board and to the ignition switch and headlight relay.
I also explain how to map information found in various wiring diagrams to the labeled areas on the circuit board. There are some places where things got confusing for me in going between the various published wiring diagram(s) and the circuit board inside the headlight shell, so I hope this material helps others avoid being confused.
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.
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
Okay, I’ve yet to achieve the first of the 12 steps for recovery: Admitting You Are Powerless Over Your Addiction. I see no problem in adding one more bike to “Brook’s Garage” inventory of BMW Airhead projects. So, I’ve acquired a 1977 BMW R100RS with about 37,300 miles. Yes, I already have the 1983 R100RS bike project, but 1977 is the first year for this innovative machine from BMW. So, getting one has been on my “Lust List” for awhile. Now, it’s in the last remaining storage space next to my car in our garage.
[Hey, maybe if I just sell the car I get 1/2 a garage for more bikes!!! But, I think that way lies divorce, so an even half dozen Beemer Bikes is the limit for “Brook’s Garage”.]
My intent is to complete a frame-up restoration of the bike, but when I start that, I haven’t decided yet. Right now I just began assembling the 1975 R75/6 “S” project bike and the 1983 R100RS was next in line; but that was before the 1977 came home. I’ll see what grabs me when I get the R75/6 “S” out of the shop.
The bike is a “10 foot bike”: It looks nice from 10 feet away :-):
“10 Foot” View
“10 Foot” View
“10 Foot” View
10 Foot View
I’ve ridden it about 75 miles and it certainly shows the value of the 40 mm Bing carburetors and lack of EPA mandated emissions modifications compared to the 1983 R100RS. It has dual plug heads, oil pressure and oil temperature senders and VDO gauges (not installed at present, so I’m not sure the gauges or senders still work), heated grips and is claimed to have the reinforced snowflake wheel installed.
The cosmetics need attention, and we shall see what surprises are inside in due course. Someone did invest in it at one time as evidenced by the modifications, but there are also signs of being parked and ignored as well.
