Rear Braking Improved

[montmil]

Over the past few months, I have worked on improving the rear brake performance on my R65s. Understanding that the rear shoes will never offer the performance of a disc system, I am finally experiencing rear braking that has gone from marginal to quite adequate.

Permit me to share what I have done and offer a few suggestions.

Measure the rear shoe lining. The minimum lining thickness should be no less than 1.5mm or 0.059 inches. If the linings are less than spec, you will need to replace them.

Check for final drive gear oil contaminating the shoes and drums. I was seeing an obnoxious gear oil drip off the final drive case that dirtied up the rim and tire before leaving its spore on the garage floor.

Previously mentioned here is the possibility of the final drive vent becoming clogged and/or closed. Located on the top of the final drive case, the unit can be removed, cleaned and, with the use of a correct sized socket and a hammer, tapped a bit to open the vent to atmosphere. The vent was not the problem on my R65.

Should the brake shoes be oil soaked but within thickness specs, consider boiling the saturated shoes to remove the gear lube. To maintain world peace, I suggest purchasing a cheap sauce pan and use a Coleman stove outdoors to cook out the oil. It works. Really.

Remove the rear brake lever from the brake cam shaft. There ishould be a felt washer between the final drive case and the brake lever. Withdraw the brake cam shaft through the interior of the final drive case. There will be a thin, flat washer on the shaft riding between the case and
the brake camshaft lobes.

The R65 brake cam shaft on your bike will likely have either two or four rubber o-rings on the cam shaft. The o-rings are supposed to prevent gear oil from exiting the final drive. Supposed to, anyway.
  

[montmil]

The o-rings are BMW-specific 10x2mm. I bought "close but not good enough" o-rings from plumbing supply stocks and two large assortments of metric o-rings from Harbor Freight but no joy. I ordered both felt washers and o-rings from Bench Mark Works http://www.benchmarkworks.com/ at $0.50 each. Buy a few extras. Droppers, I call 'em.

My 1983 R65 has four o-rings on the brake cam shaft while the 1983 has only two. Interestingly, the 81's shaft has small indentations where the third and fourth o-rings are located on the 83's shaft. Some BMW owners have machined additional grooves to add a couple more o-rings. Simple enough as the cam lobe end has a centering point for the lathe work. Measure the depth accurately and maintain the flat-bottomed groove as the OEM locations. Need squish space for the o-rings.

The position of the brake lever on the cam shaft is vital to good braking performance. In the relaxed -brake off- position, the brake arm should be a couple degrees aft of vertical. Full on brake should result in the arm being almost perpendicular to the ground. Maximum mechanical advantage will result when you stomp on the whoa pedal.

Hope this helps a few. I have finally exceeded the "plan ahead braking" of my old 1953 Triumph.

Monte

[Yikes]

Great stuff Monte, as usual.  I am about to tackle a drippy rear rear hub myself.  Got a question on those washers.  Does the felt washer go on the outside of the drum between the drum and the lever arm, and the flat washer on the inside of the drum on the right side of the cam lobes?   My ’82 was missing both and I think I installed both the felt and the flat on the outside of the hub next to the lever arm.

Thanks

[nhmaf]

Felt goes on the outside, metal flat washer on the inside.   The Felt washer tends to deteriorate quickly though.   I observed that other airhead owners would sometimes put a rubber o-ring on the outside, and the felt washer over that, which I've done with no issues.

My brake rod has multiple shallow "guide" grooves in it which, if properly milled out, would make for up to 4 locations for o-rings, but I don't have anything with which to machine them yet and haven't brought it to a shop to have it done.   With a new o-ring(s) in the usual place, it seems to be working fine.   I noticed that if you don't have the rod fully inserted through and tightened up by the lever on the outside (allowing for a bit of axial slop or play) it tends to kill the o-ring and cause it to get cut/torn quickly, and leak.   But also, don't OVERDO it on the tightness of that outside lever (by seating it really tight) or you may end up tearing up the felt washer quickly.

[montmil]

Felt goes on the outside, metal flat washer on the inside...

Yeah, what Mike says...

Suggest a little dab of plumbers silicone grease -Lowe's, Home Depot. etc- be smeared on the new o-rings to help prevent them from being cut as the brake can shaft is pushed through the hole in the final drive case.

Add a TINY bit of grease on the brake shoe pivot post and the brake cam lobes.

Lastly, you'll get to deal with the brake cam shaft slipping back into the brake drum as you attempt to refit the brake arm. I ended up slipping the rear wheel on, halfway installing the brake arm, marking its position, then pulling the rear wheel off and doing the final install of the brake lever. Grrrr...

Better braking was worth the effort and time expended.

Monte

[azcycle]

This is good stuff. I've yet to crack open the rear brake to see why mine isn't performing up to it's normal, not very good, ability. It all depended on a center stand, and now that I have that.... the rear brake is 2nd on my list behind fork seals...

I didnt' quite understand what you wrote above though... for my 81, do I need 2 o-rings, or 4 for the brake shaft?

[Mike V]

Graeme,

Should be 2 if yours is like my 81.  I just replaced mine last weekend. Those o-rings were the only things I didn't replace during my restoration and I noticed last week going down the hill from my house I had absolutely NO rear brake. No indication of oil on the rear wheel or housing. The drum and shoes were soaked with hypoid. I didn't notice anything suspect with the originals, no craks or breaks. Maybe just a littled hardened. One of those things I was going to do "later" - that infamous space in time (lesson learned). Cleaned the shoes and drum up the best I could and hoping the new o-rings seals things up back there.  My wife was home at the time so instead of using her 4-qt pot to boil I decided to degrease with brakekleen. I like the idea of adding a couple more deep grooves for additional o-rings back there.

Maybe I'll do that "later".

[montmil]

...I didnt' quite understand what you wrote above though... for my 81, do I need 2 o-rings, or 4 for the brake shaft?

And that's the rub, Graeme. You won't know until you pull out the brake cam shaft! My '81 has two o-rings. The '83 has four o-rings. One day I may whittle a couple extra grooves for the '81's shaft.

Being a sorta belt n' suspenders guy, I bought eight o-rings and four felts. Call 'em spares, droppers, whatever. At only fifty cents a pop, figured I'd stock up.

Monte

[Rob Valdez 79 R65]

...and the early models ('78-'80?) don't have any o-rings on that brake shaft.

At least that is what I have heard.  I've never had mine apart.

[montmil]

...and the early models ('78-'80?) don't have any o-rings on that brake shaft.

At least that is what I have heard.  I've never had mine apart.

True about no o-rings for the earlier design for the brake cam shaft pass through. I wonder if there was no opening to the final drive gear oil reservoir as on the later bikes. I semi-sorta recall reading about shaft seizures and galling plus the need to occasionally pull the shaft and apply grease.

We're back to the farm implement.

Monte

[Barry]

Yes - there are no O rings on the 78 - 80 models and no connection to the final drive oil.

Maybe Tractor technology is best in this case. Clean and grease the old type once or twice every 30 years and it will work just fine and never leak.

[azcycle]

Ah, okay well I'll order a bunch and see what I've got when I crack it open.  On the same topic, I noticed that the pedal actually swung down quite low before engaging the brake, so I tightened up the adjuster bolt all the way in (tire wouldn't move) and then slowly backed it off until there was no rubbing anywhere.

Went for a ride around the block... and at low speed (>10mph) hit the rear brake... and locked up the back tire! I couldn't do that before... Braking definitely improved, and felt much more confident on the commute in this morning.  I need to look in there and see how much lining the shoes have left but at least for the time being I "solved" the bad rear brake.