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Thread: R75/5 Final Drive burp

  1. #1
    Registered User ebeeby's Avatar
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    R75/5 Final Drive burp

    I changed the final drive grease last year. Since it showed low (below lower thread) upon draining, I looked up the exact amount required in the BMW shop manual which is .25L or about 8.7 ounces. It took some doing (driving, re-checking) to get all that in the final drive as that grease is heavy and takes time to settle in, but I did it.
    In June this year on a 40 mile run, I burped out grease from the top vent, enough to get on the tire not just some spots on the rim. I wiped it down, and I don't think it burped again on return trip. Last night, 10 mile run, it burped out a small amount, just enough to show on the outside of the final drive. I pulled the fill plug and grease was below lower thread. To determine how much below, I added grease and it took about 1 ounce to come up to the lower thread.
    Question: Since in the last 15 years I probably never had the exact full amount in the final drive until the change last year (I did other changes, but just filling to lower thread, turning rear wheel, adding a little etc., not forcing 8.7 ounces in) is it just burping to its preferred level which appears to be 7-7.7 ounces?
    1973 R75/5

  2. #2
    Liaison 20774's Avatar
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    I would go back to your "old" ways! Fill to the bottom of the threads, maybe spin the wheel, and see if you can get some more in. The pinion gear is running in a bath of oil with the fill at the bottom of the threads. It doesn't really go bad, certainly not by heat, although it might be sheared up over time with the meshing going on. So, bottom of the threads should be fine. I found a /5 manual online and it says 0.5 pints which is 0.236 liters, so if you're going to 2.5 liters, that might actually be too much.

    What is the weight of the gear oil? I would not use something like 75W140 but rather stick to the 80W90 that was called for.
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    '78 R100/7 & '69 R69S & '52 R25/2
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  3. #3
    Registered User ebeeby's Avatar
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    Yes, 80/90 Valvoline hypoid gear oil. Interesting, the BMW shop manual calls for .25L....

    In any case, the variances involved seem to be 1 ounce or less...
    1973 R75/5

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