From the Airheads mailing list

I see a question and comments about improving front braking on a 1978 R80 from a single disk to dual. One person said go to brembo brakes.

It can be done, but prepare for a snowflake front wheel, the spoked one won’t fit with Brembos. Also you will need the later model down tubes as the attachment of the dampeners is by different means. So you just can’t replace the lowers. (But you can use the originals, if one can get some parts machined).

The wheel cylinders were of different sizes, there are some 38 MM units and some 40 mm units, the 40s give more brake power, the R75s and 80 had 38s. The R100 units and later (75 – 76) and R90S had 40s. So look at the cylinders, it is stamped on there some where. You can’t go by colors, some are silver, some black, the blue anodized ones were 40s probably they came on the 77-79RS.

Brakes going bad can be most easily corrected by changing the fluid yearly, replacing the soft hose(s) to stainless. Using new cables and keeping the pivot points lubed and the contact area of the pad to rotor adjusted properly on the ATEs. On handle bar master cylinders one needs to check the sizes on these also, there are some sized for the smaller diameter that give more pressure per square inch on the wheel cylinders but also requires more hand travel. Brake pads other than stock also help but can be hazardous in rain. For example, Ferodo stop good when dry, but when it rains one must keep putting on the brakes to dry them out. That my 2 cent worth on older front brake systems.

There is an extensive articles on brakes in the following article. It includes a section on improved braking, with photos of some installations.  Brakes from many Oilhead and Classic K bikes are relatively easy to adapt.
http://bmwmotorcycletech.info/brakes.htm

John Davidson