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Thread: Final drive leaks oil 99 RT

  1. #1

    Final drive leaks oil 99 RT

    I have a 99 RT that leaks oil from the vent cap on the top of the final drive. It only happens on long trips when the bike is loaded up with extra weight ( camping gear, etc. ) I have made sure the fluid level is at the correct level and that the vent cap is clear and unobstructed. It pukes oil from the vent cap which gets all over the rear rim and sides of the tire which is a PITA to clean up not to mention a possible safety issue. Any insights for a possible cause/fix would be greatly appreciated. Thanks, Gregory

  2. #2
    Registered User GTRider's Avatar
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    How have you verified lube level-drain and fill to spec per the manual, or inspection at the fill plug? What type and viscosity of gear lube are you running?

    Best,
    DeVern
    DGerber
    1983 R80ST — 1984 R80 G/S-PD — 2004 K1200GT w/Hannigan S/C — 2010 K1300GT — 2018 R1200GS
    BMWMOA#52184, AMA#271542, IBA#138

  3. #3
    Quote Originally Posted by GTRider View Post
    How have you verified lube level-drain and fill to spec per the manual, or inspection at the fill plug? What type and viscosity of gear lube are you running?

    Best,
    DeVern
    I'm running Redline Shock proof since day 1. Has 90w viscosity. Fill final to spec. which is to the bottom of the fill plug threads.

  4. #4
    Registered User GTRider's Avatar
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    The most common causes I’ve seen for pushing gear lube out the vent are over-filling or incorrect viscosity, exacerbated by high-speed running with a stone cold FD unit. BMW spec for that drive is 75w-90, and while Redline offers three different levels of Shockproof, in their advertising and sales materials none of them are clearly labeled with a viscosity, only a loose viscosity comparison. The first BMW I had (and still have) was parked in an unheated space and on a cold morning (30F or so) would push lube out the breather if not warmed up at low speed. The temporary fix was switching to a synthetic 75w-90 lube after draining while warm and refilling with the specified (updated) quantity of lube. Long-term fix was an insulated garage that never gets below 45F or so, and since it has been quite happy with Castrol 75w-90.

    If it were my bike I’d do a warm drain and a refill with the correct quantity of verified-viscosity lube—and check the SI bulletins for any updates on quantity then ride it to see what happens. Syntrax 75w-90 if you want to stay with synth. You’re out only a qt of fluid and a couple of crush washers should you elect to switch back.

    Just my $0.02,
    DeVern
    DGerber
    1983 R80ST — 1984 R80 G/S-PD — 2004 K1200GT w/Hannigan S/C — 2010 K1300GT — 2018 R1200GS
    BMWMOA#52184, AMA#271542, IBA#138

  5. #5
    Kawa Afterthought weschmann's Avatar
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    Quote Originally Posted by GTRider View Post
    The most common causes I’ve seen for pushing gear lube out the vent are over-filling or incorrect viscosity, exacerbated by high-speed running with a stone cold FD unit. BMW spec for that drive is 75w-90, and while Redline offers three different levels of Shockproof, in their advertising and sales materials none of them are clearly labeled with a viscosity, only a loose viscosity comparison. The first BMW I had (and still have) was parked in an unheated space and on a cold morning (30F or so) would push lube out the breather if not warmed up at low speed. The temporary fix was switching to a synthetic 75w-90 lube after draining while warm and refilling with the specified (updated) quantity of lube. Long-term fix was an insulated garage that never gets below 45F or so, and since it has been quite happy with Castrol 75w-90.

    If it were my bike I’d do a warm drain and a refill with the correct quantity of verified-viscosity lube—and check the SI bulletins for any updates on quantity then ride it to see what happens. Syntrax 75w-90 if you want to stay with synth. You’re out only a qt of fluid and a couple of crush washers should you elect to switch back.

    Just my $0.02,
    DeVern
    If filling to fill line I believe you are putting too much fluid. 180 ml has been a standard which is what I have been putting in my 94 RS. At 180 ml, I was not at the fill line. Sounds to me like when it's getting really hot, it's building up too much pressure and blowing like a pressure cooker relief valve. Check your manual for the exact ml amount you should be adding and go with that amount. See if you have better results.

  6. #6
    Thanks to everyone for the reply's. Interesting part is it never seeps from the vent when there is no extra weight on the bike just when its loaded up with gear for a long ride. I'm going to drain the FD and fill it with a different 75-90w to the exact mil. measurement. and see what happens. Thanks again, Gregory

  7. #7
    I referenced My Haynes manual and it says the FD takes 230 ml. Can someone clarify which is the correct amount 230ml or 180ml. Thanks

  8. #8
    MOA #24991 Pauls1150's Avatar
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    230 is the old number from the BMW service manual, but Haynes doesn't update their books very often. Their torque values are another gross example of this.
    I just take it up to a hair below the bottom of the threads with the bike on the centerstand.
    Never had an issue (incl. multiple coast-to-coast and Mexico to Canada trips, where the bike was certainly loaded up)... and I always used a quality 75W-90, GL-5 rated juice. NOT GL-4...
    Maybe your choice of oil simply has a higher coefficient of expansion when hot than what is expected or typical -?

  9. #9
    Pepperfool GSAddict's Avatar
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    From the OE manual
    Attached Images Attached Images
    Last edited by GSAddict; 07-09-2021 at 03:21 PM.
    '
    Ufda happens..........

    Need your R11xx Hall sensor rewired? PM me.

  10. #10
    Registered User m_stock10506's Avatar
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    Just note that there is a typo in the engine oil fill amount. Without a filter change would be 3.5 liters, not 5.5.
    Michael Stock, Trinity, NC
    R1100RT, R100, R60/6

  11. #11
    Pepperfool GSAddict's Avatar
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    Quote Originally Posted by m_stock10506 View Post
    Just note that there is a typo in the engine oil fill amount. Without a filter change would be 3.5 liters, not 5.5.
    Corrected (to prevent air box from filling up......)
    '
    Ufda happens..........

    Need your R11xx Hall sensor rewired? PM me.

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