I rode a friend's '81 R100 RS with the EBC floating rotors and the difference was ama-ZING. Now to be clear, he's a mechanic and keeps his bikes in tip-top condition, plus the '81 has 2 Brembo dual acting calipers. However, it was more than impressive. The brakes responded like the bike was a showroom-fresh 2017 BMW or Ducati.

You've not indicated the concern or issue driving your query, but here are some additional thoughts...
► Unless you have badly scored discs and need to spend that type money, you'll get a better response for your money by replacing the stock rubber brake hoses with what's commonly called "stainless steel hoses". What the general public doesn't understand is that the "rubber" hoses often collapse internally and block fluid flow. (I see this with regularity. The failure rate is really scary.) Plus if you simply lay your hand on the hose and squeeze the brake lever, you can actually feel the stock hose expanding. That's YOUR energy intended to expand the caliper, being wasted to NO useful end.

► With hydraulic brakes, new fluid is always the place to start. DOT 4 type fluids should be changed annually, and have a nasty habit of leaving residue build-up inside the master cylinder and caliper(s) if not. Actually, even if it was changed, face it, you got a 40 year old system. Some build-up is bound to have occurred. Most of the time the m/c and calipers can simply be disassembled and cleaned to restore 100% operation, that is, if you're early in the cycle and leaks haven't set in yet.

Hope this helps.

PS. I'm in need of a single disk to replace my deeply scored rear disc. If this upgrade leaves you with a good spare, I'd be interested to hear a price.

I do have stainless steel hoses, gotta have'm the rubber real does stink...
Master cylinder recently serviced, fluid new.
New EBC pads, system adjusted properly.
No real problems with the operation of system. But I am an aggressive front brake user o entry.
(I'm a bit old school, rear brake evil, more for stability and set up)
Rotors are scored and you can feel the grooves in both and they are 40 years old.
The real fix is to replace the lower with 1980 and up and eliminated the crappy floating caliper system. But then I believe I might lose the clearance for a spooked wheel...

I do not know if a "77" front will fit the rear...

New BMW rotors are $450.00 each. ouch....... $1000 a pair...a third the cost of a replacement bike...

Then you might also wish to investigate a master cylinder with a smaller diameter bore. Something around 13mm. You'd want that handlebar mounted too.

A friend here found an entire K bike front end on Ebay which gave him larger diameter fork tubes, dual Brembo calipers, and the front axle set in-line with the stanchions (for more responsive handling). It used his existing front wheel. Bolt-on magic for about $250.

Any chance you could provide photos? Spoked wheel?
I did not now K-bike front ends were proper dimensions, that would be easier to find.
I know the Master cylinder works best at the highest point, but I've always liked the cleaner look of no hoses.
(less is more, when it comes to cosmetics in my book...)

I know the Master cylinder works best at the highest point, but I've always liked the cleaner look of no hoses.

That's not why I suggested handlebar mounted m/c. The mechanical cable also allows some stretch, and thus loss of braking efficiency. You said you liked using the front brakes, well, the newer method is the better method and uses a lot less parts.

I'll find out more about my friend's bike.

Where can I obtain a 13mm under-the-tank master cylinderfor my 77 R1100/7?
Thanks

I installed the EBC rotors on my 92' R100R about 3 years ago and they work great. All the stopping power of stock at half the price!