Boxerworks.com

1984 R100
So I've replaced the O rings on the rear brake cam. I've greased and reinserted the cam. Now I've got to figure out where the cam needs to be positioned to install the rear brake actuating arm on the splines. I'm sure I marked it, but I can't see where. I guess I needed to use a pointed punch

Any suggestions?

Boy, you'd think there'd be a reference.

I've done it by trial and error. Wheel back on and put the lever where it feels natural. Then operate the lever by hand and see if the brake shoes make contact just before the lever would be at 90 deg to the rod. The goal here is to have the lever at 90 deg to the rod when the brake is on, for best leverage.

melville wrote: ↑Sun Aug 21, 2022 11:11 pm Boy, you'd think there'd be a reference.

I've done it by trial and error. Wheel back on and put the lever where it feels natural. Then operate the lever by hand and see if the brake shoes make contact just before the lever would be at 90 deg to the rod. The goal here is to have the lever at 90 deg to the rod when the brake is on, for best leverage.

Thanx Mel!
So it doesn't matter where the camshaft is located before attaching the actuating lever on the right side. There is a BMW mark on the cam. I'm assuming that should be facing up?

Agree, 90 deg when the brakes are applied for maximum mechanical advantage. There is no other logical position.

melville wrote: ↑Sun Aug 21, 2022 11:11 pm Boy, you'd think there'd be a reference.

I've done it by trial and error. Wheel back on and put the lever where it feels natural. Then operate the lever by hand and see if the brake shoes make contact just before the lever would be at 90 deg to the rod. The goal here is to have the lever at 90 deg to the rod when the brake is on, for best leverage.

There is no 'right' position, hence no mark. It depends on the thickness of the lining which will change over time with wear. Drum shoes last a long time but at some stage, the angle between the arm and the rod will get to the point where it is significantly beyond the 90 degree point and the braking efficiency will start to decline. At that point you remove the arm from the splined shaft and move it back by one spline to get back to the ideal setting.

Rob

Question about the cam lobes. I seem to remember a manual saying that there is a "this side up" for the actual cam that the brake shoes sit on.

Tom

Thanx all!

I'll give it a try. Must do better marking. Would finger nail polish work?

Zombie Master wrote: ↑Tue Aug 23, 2022 4:44 pm Thanx all!

I'll give it a try. Must do better marking. Would finger nail polish work?

Depending on the crowd you hang out with, fingernail polish might work for you.

As far as your brake arm goes, just put everything together and apply the brake.
With the brake firmly applied, the arm should be perpendicular to the rod (90 degrees).
If it's not, pull the arm off the spline and reposition it as necessary.
There is no pre-set spot or reference point per se.
As Rob F said, "It depends on the thickness of the lining which will change over time with wear."
I

Should the BMW mark on the cam lobe be facing up?

Zombie Master wrote: ↑Wed Aug 24, 2022 2:37 am Should the BMW mark on the cam lobe be facing up?

Sure why not?
but it actually doesn't matter.