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Thread: '81 R80 G/S Final Drive sprung a leak

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  1. #1
    Day Dreaming ... happy wanderer's Avatar
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    '81 R80 G/S Final Drive sprung a leak

    Went for a great ride up into the local mountains and on my way discovered my rear brakes were useless. Nothing wrong with the adjuster and I knew I had plenty of brake material left from a recent inspection and adjustment. Opened it up yesterday and found a big mess in there. So farI am guessing I need to replace the main bearing shaft seal and the gasket for the housing cover. Brake shoes will be toast now too with gear oil smeared on them.

    What seems strange at first glance is the main bearing seal does not really appear to be leaking. There is also a bit of mess outside the breather cap. It was clear last time I checked it as well. Not really sure where the oil came from yet but it seems to be mainly on the shoes.

    Are there any other points of gear oil ingress that I am not seeing on the fiche? I've never had one of these go on me in all these years so I'm in new territory.

    IMG_20130921_145544.jpgIMG_20130921_145531.jpg
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

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    Administrator 20774's Avatar
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    Could there have been a leak along the rod that passes through the final drive that operates the brake cam?
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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    Day Dreaming ... happy wanderer's Avatar
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    Quote Originally Posted by 20774 View Post
    Could there have been a leak along the rod that passes through the final drive that operates the brake cam?
    You know Kurt I was looking at the cam trying to figure that out and it totally makes sense because that is where the biggest collection of crud is. As I said I have looked at the fiche but have not started to pull it apart yet. After reading your post I looked again and just now realized it goes right through and there is a sealing O Ring there. I bet that it is defective and that's how the oil got in.

    I'll report back once I dig into it some more. Spending some quality time with the oilhead to make sure I have a bike to ride to the "Last Chance to Ride n' Camp" next week! If I can get the G/S fixed in time I'd rather take it and have some gravel fun on the way home. If it's just an O Ring and a cleanup job plus brake re-shoeing that would be great news.
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

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    Registered User helmut_head's Avatar
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    Buy new brake pads while your replacing those cam seal O-rings. Save on shipping.
    Helmut always wears a Helmet.

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    Day Dreaming ... happy wanderer's Avatar
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    Quote Originally Posted by 20774 View Post
    Could there have been a leak along the rod that passes through the final drive that operates the brake cam?
    I have it all apart now and I think you nailed the problem Kurt. The two O Rings are pretty flat, there was oil getting past the inner one when I pulled the rod out as well. There is also supposed to be a felt washer in front of the metal one and there wasn't one there. Missing, never installed or disintegrated... who knows.

    Anyway, thanks for steering me there. Local shop where I get airhead parts tells me it's a common occurrence. It would be nice to get off easy if it turns out that way.
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

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    Administrator 20774's Avatar
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    A fix that doesn't cost much but your time is a good one!
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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    Registered User m_stock10506's Avatar
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    Quote Originally Posted by happy wanderer View Post
    I have it all apart now and I think you nailed the problem Kurt. The two O Rings are pretty flat, there was oil getting past the inner one when I pulled the rod out as well. There is also supposed to be a felt washer in front of the metal one and there wasn't one there. Missing, never installed or disintegrated... who knows.
    If possible, pictures would be appreciated!!! If not, as much detail of the repair as you can provide. I might be looking at the same issue on my R100. If got a few drops of gear oil coming out of the drum brake cavity on my return from a ride. I'll be pulling the wheel soon to look at the inside of brake drum and see if that's where the leak originates.
    Michael Stock, Trinity, NC
    R1100RT, R100, R60/6

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    Day Dreaming ... happy wanderer's Avatar
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    Sorry it's too late for pictures as it is back together already. One day to disassemble and go get two O Rings and a felt washer. One day to clean up the mess and reassemble. I cheated and used gasoline first, acetone second and brake cleaner last to get the shoes clean and dry of any gear oil residue. Then I roughed them up slightly with some sandpaper for good measure. I know some of you are cringing at the thought but I think they will be fine. If not, I'll replace them later.

    This is not a difficult job and the steps are as follows:
    - Remove the wheel
    - Remove the circlip holding the brake shoes on the front pivot point. Not shown in drawing below but it is there.
    - Grab the top shoe at the top, bottom shoe at the bottom and pull towards you. The spring tension holding them tight will collapse inward and they will "pop" off the cam at the rear and the pivot point at the front.
    - Remove the wing nut (12) the brake lever (11) and pin (10). The brake lever is splined. Finding no factory alignment mark, I put a center punch mark on the outer end of the brake cam pin at the gap on the brake lever so I could replace it exactly as it came off.
    - Slide the brake cam out of the housing noting the order. Cam shaft, washer, felt washer. You will (should) find two O rings on the shaft looking tired or flat and unless there is extraordinary wear on the cam shaft worn O rings are probably where the leak is. This is what I am hoping anyway. I found no felt washer on mine at all.
    - Examine the main seal and if it looks OK just clean the mess up. I use varsol and a parts cleaning brush for this. Do the same on the brake drum/wheel side. Then use brake cleaner and lots of air on both to get the solvent or whatever your favourite degreaser is off of everything.
    - Reassemble with new o rings, felt washer. Make sure the cam shaft passageway through the housing is clean and clear of any residue. I use red rubber grease on any and all o rings nowadays. Re-insert the cam shaft and replace the brake lever, pin and wing nut but leave it slack for now. (easier to get the wheel/drum back on)
    - Put both springs back in the shoes and pop them back on the same way they came off (at an angle then push them outward and in. I put a thin film of MolyKote on the ends of the shoes where they rub on the brake cam. Like hardly any. Replace the circlip that retains them.
    - Install the wheel and adjust the wing nut until the wheel won't turn then back it off until the wheel turns and you don't feel or hear resistance from the shoes.
    - If you drained the final drive you should refill it now


    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  9. #9
    Registered User jimbc's Avatar
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    Mine leaked too.

    As you know there's a tube that's pressed into the diff housing where the brake cam goes.

    Mine was leaking from the area between the tube and the diff housing. When I took it apart I had the 2 o-rings on the brake cam and a 3rd but damaged one that went between the metal washer and the diff housing on the inside. My local dealer was unable to I.D. the 3rd o-ring so I drained the fluid, cleaned the area, applied Loctite 290 to seal the space between the tube and diff housing, let it cure and then added silicone (used to seal automotive diff covers) to fill the recessed area where the damaged o-ring used to reside. This was in the spring of this year and so far no more leaks.

    I've since found the damaged o-ring p/n (20 35 21 1 457 605) on the Max BMW fiche.
    1985 R80 Original owner

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