74' Disc Brakes
I am looking at purchasing a 74' R90, unknown mileage, very good driver condition.
I am concerned about the disc brake though. The owner said the master cylinder has been rebuilt. The front brake does not stop the bike like I believe a disc brake should. It feels like an old drum brake. No modulation, no grab, just a hard wood like feel to the brake lever. I cannot get it to lock the front wheel up no matter how hard I try.
What is the collective consensus about this? I am not opposed to rebuilding or replacing the master cylinder and or caliper if need be, I just would like to know if this brake is normal or should the disc brake be more like the modern day disc brakes? ...yes I know this is a 1974 single disc and will not be like a 2013 system.
Thank you in advance.
The ATE caliper and pad probably need to be adjusted for maximum contact. The solid disk for the '74s was not the best...the drilled rotors from '75 were better plus helped with wet conditions. You could consider other changes such as non OEM pads, steel brake line, and a handlebar master cylinder. These types of changes have been noted by others in the past to improve the braking. A more radical approach would be to convert to dual disks which requires buying the slider, changes to the master cylinder (maybe), and the second rotor.
I'd guess it is normal for that bike... the single disc on my /7 was the same way. I tried a number of different pads, careful adjustment of the caliper, and a new rotor, but could not get satisfactory results. I've heard that the single disc ATE was referred to as the original BMW antilock brake system. I finally gave up and converted it to dual disc with floating rotors, which I am very happy with and would do again... but it's not a cheap fix.
There is no comparison to a modern brake system. A 1974 front brake is slightly better (maybe) than drum brakes. Make sure it is set up properly and maybe invest in a SS braided brake line.
I replaced my original rotor with an ebc one. Replaced pads with ferodo sintered pads and adjusted the front caliper. Now ebc makes a sintered pad to fit the airhead, but not the HH pads I wanted. After they wore in they work ok. Not great but much better than when I bought it. I am probably going to replace the under the tank master cylinder with a handlebar mounted one. There was some posting on boxerworks on how to do that little project. According to the aussie that did that conversion it made significant improvement.
Thanks folks...this is great information. Now I know there is hope for the front brake on this bike.:dance