1982 R100 Brake Drum Worn on Snowflake Wheel ?

PoorUB said:

I have to wonder if you are looking in the wrong place. I find it hard to believe that the brake shoes and drum could be bad, or be bad enough to give you pretty much no breaking. Have you looked over the linkage well and made certain it is in good condition and properly installed? I wonder if something is wrong with the linkage, binding, or perhaps installed wrong giving you a wrong ratio, wrong action?

Click to expand...

Along the lines of the linkeage being the source of your problem, be aware you can install the cam that attaches to the external brake arm backwards. When you do, the cam does not expand the shoes fully and you get limited braking. This fits your observation of only part of the shoes showing wear because the cam didn't open them all the may, so only the leading edge of the shoes touched the drum.

I suspect when you replaced the shoes with new EBC shoes, you rotated the cam 180 deg and now have it installed correctly. So, now you have a rear brake.

The brake cam is (23) in this diagram.



The cam surface is not symmetric so rotating it 180 deg changes how much it lifts the shoes.



Hope that helps.

Best.
Brook Reams.

Rod, I'd recommend that you take the wheel off and look at that cam again: the difference in the lobes isn't immediately apparent to the casual observer, and if it's still backwards (rotated 180°), you'll have the same issue again.

EDIT: Alternatively, considering that the shaft is captured by the brake arm (#14 in Brook's pic), is it possible that the cam is only off by a spline or two? That might cause a similar issue. Only a detailed inspection will solve it for sure.

Here is a shot of the end of the splines and the arm. When I installed the new "O" ring about a million years ago, I scribed a line across both parts to match up and maintain alignment.
You can just see it in this photo. At about the 10:00 position, from this angle. For some reason the photo rotated when I uploaded it. Of course that doesn't mean it was correct when I got in there ?

I believe this is the correct orientation of the rear brake cam.





Best.
Brook Reams.

Bear with me as I am not well versed on R100's. The brake lever on the rear hub should be close to 90 degrees to the linkage rod with the brakes applied, probably just coming up to 90 degrees with new shoes so as the shoes wear the arm with come closer or just past to 90 degrees. If the arm is way off from 90 degrees you will loose braking power, meaning you will have to push harder on the foot pedal to get decent braking.

I have seen this issue on Japanese imports where "mechanics" have put them back together wrong.

At this point i would disassemble everything and lube all pivot points to be sure everything is working correctly if you haven't already.