1983 R65LS brake actuating arm rear wheel

[suecanada]

I saw a great looking brake arm on the Motobins parts internet site. But, the actuating arm was for R65's from 1985 onwards. Does the 1985 monoshock R65 by chance use the same actuating arm as my twin shock 1983 LS?....anyone know?? Motobins sales pointed out the discrepancy as I had missed the '85 onwards description.

The reason Motobins arm looks good to me is I can see a couple of square grooves for O-rings at either end of the arm!! Not that expensive either.

[Bob_Roller]

Hi Sue !!!

Is this the part from Motobins ??

P/N : ZZ35034

Looks the same as the earlier bikes, but those extra grooves are too shallow to allow extra o-rings to be used .

They are not located where they would be sealing against the final drive case, they would be in the area between the two parts of the final drive case .

[suecanada]

Hi Bob, Thank you for replying!
Yeah, the middle grooves are too shallow for sure but what I have now has ALL shallow grooves! No square ones at all, let alone at the ends for O-rings..hence there is leakage. Rather than get my brake arm machined with 2 end square grooves, I figure I might as well get this part from Motobins if it is the correct part for my '83 LS. Somehow I don't have enough faith in a machinist knowing what to do and me trying to explain it!
Maybe I am incorrect but the Motobins part "looks" to have 2 square grooves...one at each end of the rod where they might be able to seal against the case walls. You see no square grooves then?
I have a question in to Motobins about square grooves being present but just wanted to know if the part was even correct for an '83LS.

[Bob_Roller]

I searched RealOEM parts site  and found that the first generation R65, '78-80, has a specific  rear brake cam .

The second generation, '81- '84 have a different part number and the '85  (monoshock ) and later bikes have a different part number as well .

So, the best I can tell, no the Motobins part won't work .

Don't know the differences between the two later model parts .

The cam shaft you have, may be from a first generation R65, those final drives had some sort of sleeve through the cases and didn't need the o-rings on the shaft .

[Barry]

The first generation R65, 78-80 brake cam never did have O rings but didn't need them because with the earlier smooth case diff the shaft was not open to diff oil. The shaft was greased on installation and the shallow grooves are intended to retain a little grease.

The second generation 81-84 brake cam did have O rings because the shaft was open to the diff oil on the later ribbed case diffs. Presumably it was intended as a means of lubing the shaft but it was rather too good at that and while at first two O rings were fitted, later they had four in an attempt to keep the oil in.

It has been suggested that another way to keep the oil in is to lower the  fill level a little. 

Given the LS models must all have the ribbed final drives and a brake shaft open to the diff oil I'm Surprised to hear they came with a shaft that didn't have O rings fitted. You have to wonder if it is the original part or one substituted from an earlier model.

[suecanada]

Barry I measured the oil in the final drive when I had no leak and it was down to 235 cc. from the 330 cc I put in it. Surely that is too little. The specs want 350 cc. Any thoughts as to how many or how few cc's I can get away with without damage to the FD?

The Driveshaft retains its oil just fine.

[suecanada]

Sales dept guy at Motobins measured their arm at 95 mm from inside cam edge to end of spline. Anyone have an old one out to measure it from a '81 to '84 time period?

I remember Snowbum said BMW made a whole bunch of reiterations of these arms with a variety of groove numbers but the square ones are what I am interested in. The number of square ones probably doesn't matter much but at least 2 should be present at the opposite ends.

[Barry]

Barry I measured the oil in the final drive when I had no leak and it was down to 235 cc. from the 330 cc I put in it. Surely that is too little. The specs want 350 cc. Any thoughts as to how many or how few cc's I can get away with without damage to the FD?
 

Sue,

The oil level isn't critical but I agree 235 cc is too little and if the brake cam still leaked at that level then lowering the level is not a solution.

See attached for where the reduction in level idea came from.  20cc is a small reduction but of course he's referring to a shaft with O rings already fitted.

[suecanada]

Well I put 330cc back in and it's been happily leaking out the spindle....when it stops I'll  empty it again and measure the quantity that comes out. This will be interesting. Thank you Barry.

[Tony Smith]

The final drive is splash lubricated by the crown wheel throwing oil about inside the housing.

Any oil level that immerses the teeth will be sufficient in my opinion for lubrication, the unknown is to what extent the oil is there to cool things - that I do not know.

But I can say with sureity that when my seal failed and the drive flung oil all over the RHS of the rear wheel (something I didn't know until I cranked with some enthusiasm into a Right hand corner) that I drained the oil down to a level that meant that the bottom teeth only were immersed and then rode it 200km home with no problems.