R80 ST Brake Cam Questions.

[Tom H Ca]

I'm helping a friend with a weep that looks like it's coming from the brake cam shaft. We pulled the brake cam and found 4 O rings on the shaft. Figured we would get 4 new O rings, looked at the parts list and the confusion set in.

When we pulled the cam, gear oil came out from the brake side and the outside of the hole the cam rides through. Should that happen??
If I read the parts list right, there is a tube that MAY?? seal the cam shaft hole.

The O rings have 2 different sizes. I think that by the month made, that will tell us which to use.

But a confusion is what parts are needed on the cams shaft. What came out was:

While holding the cam section (the area the brake shoes ride on) in your left hand and working you way out to the lever:

We found a metal washer, the 4 O rings on the shaft, and then the lever for the foot pedal.

Per the parts list, we may or may not be missing a felt washer????

What do we need to seal this?

Thank you,
Tom

[barryh]

I'm helping a friend with a weep that looks like it's coming from the brake cam shaft. We pulled the brake cam and found 4 O rings on the shaft. Figured we would get 4 new O rings, looked at the parts list and the confusion set in.
When we pulled the cam, gear oil came out from the brake side and the outside of the hole the cam rides through. Should that happen??
If I read the parts list right, there is a tube that MAY?? seal the cam shaft hole.
The O rings have 2 different sizes. I think that by the month made, that will tell us which to use.
But a confusion is what parts are needed on the cams shaft. What came out was:
While holding the cam section (the area the brake shoes ride on) in your left hand and working you way out to the lever:
We found a metal washer, the 4 O rings on the shaft, and then the lever for the foot pedal.
Per the parts list, we may or may not be missing a felt washer????

What do we need to seal this?

Thank you,
Tom

The history of this arrangement is that prior to 81 the hole for the brake cam spindle did not communicate with the oil in the final drive so no leakage was possible. The spindle was simply greased and a felt washer was definitely uses on the inside.
Starting 81 the hole was opened up to the final drive oil for lubrication first with two O rings fitted and then with four in an attempt to contain oil leaks. The sleeve you mention was the final attempt to cure the problem taking the arrangement back to how it was prior to 81. There is a suggestion here from someone who was in the trade at the time as to how you might eliminate the leakage.

Brake cam.png (71.88 KiB) Viewed 681 times

[Rob Frankham]

OK, this is what it looks like to me...

Prior to 03/83 there is a sort bush 24mm long that fits into the inner case and 2 of 10 x 2mm 'O' rings.
From 03/83 the bush was replaced by a pipe 84.5mm long that bridges the gap between the two cases. The two O' rings were retained. The rear brake cam was also replaced.
From 09/83, the two 'O' rings were deleted and replaced by what is described as a gasket ring measuring 12x1mm.

The sheet metal washer fits between the cam itself and the inner cover. The felt washer fits on the shaft between the lever and the outer case. I believ there is a recess for it there.

I can see no fitment for 4 'O'rings of any size... perhaps this is an anomaly perpetrated by a PO.

If the bike your working on has the ling pipe/bush there should be no oil leaking from the shaft. If there is, then it's is probably leaking from the joint between the 'pipe' and the case so it may be a case of sealing that joint...

Rob

[Tom H Ca]

I will have to find the build date for it.

I do not know if there was any sort of tube in the hole for the shaft. Again, pulled the cam and gear oil started flowing out from both sides. So....To me that would say there was no tube. OR...If it had the short tube, would it flow out when the cam is removed?

For the O rings. It did have 4 on the shaft. The size should be 10 X 2mm correct?

Also, there was no felt, not any recess for it. If I did use one, it would just be slid against the case and held in place by the brake lever.

Thank you very much so far!!
Tom

[Rob Frankham]

Build date is easy... just put the VIN into the REALOEM website (https://www.realoem.com/bmw/enUS/select?) Parts Catalogue and read off the month and year from the last column...

Rob

[Tom H Ca]

A silly question. A 10 X 2mm O ring. Is the 10mm the ID or OD. I have 6 ID X 10 OD X 2 or 10 ID X 14 OD X 2

Thanks again,
Tom