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Thread: Final drive vent

  1. #31
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    Item 20.
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  2. #32
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    How much different is the pre 1981 model final drives that they didn't require this "protection plate"? The fiche says it began use in 9/1980. Why don't the earlier FDs spew oil??
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  3. #33
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    Different casting and vent

    I would have to say its the shape of the casting and the vent itself is built differently. The problem with making a puke line for it is you can run the gear oil right out of the F/D on a long ride and damage it. I would have to guess that the F/D's out there without the baffle were resealed at one point and the wrench that did the work got it back together then realized the baffle plate was still on the bench. Didn't want to waste a gasket so the baffle got tossed. There's a ton of those late model F/D's out there so I'm sure someone will have a spare one you pick up. Takes about three hours and $25 in parts to pull one apart and reseal it if you don't have to re-shim or put new bearings in. Mark Hugget may have those baffles, he seems to have a lot of N/L/A stuff.

  4. #34
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    Apparently my final drive doubles as a hydraulic pump. Took it out this morning. Went about 10 miles no faster than 45 mph. No oil in the vent tube i installed. Hit the highway and did about 4 miles at 70-75 mph and this picture was the result. Got back home and nearly all the oil had drained back into the FD. Lost no oil and the rear tire stayed dry. Thanks for all of the help.
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  5. #35
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    Quote Originally Posted by ocoinji View Post
    Apparently my final drive doubles as a hydraulic pump. Took it out this morning. Went about 10 miles no faster than 45 mph. No oil in the vent tube i installed. Hit the highway and did about 4 miles at 70-75 mph and this picture was the result. Got back home and nearly all the oil had drained back into the FD. Lost no oil and the rear tire stayed dry. Thanks for all of the help.
    Are you going to do a proper repair with a baffle?

  6. #36
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    Yes, but probably not until the riding season is over and the bike is in my basement. This fix just keeps me riding for now.

  7. #37
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    One thing that probably isn't helping your situation any is that it appeared that the cap of your vent was shoved all the way down to the top of the threaded nut insert in the final drive. It should be up above the top surface of the nut by a few millimeters so that it is open to normal atmospheric pressure through the tiny holes at the top under the mushroom cap. Otherwise, it may be that there is no air flow/venting going on, and as the final drive heats up under high speed riding, things expand (including the air inside the drive) and it forces things to squirt out under pressure. I have seen this happen on final drives where the oil is forced out of various seals in the final drive, coating the rear wheel in FD gear oil. Simply making sure that the little vent holes in the top of the cap were not plugged, and ensuring that the vent was not shoved all the way into the sleeve of the final drive (it should look like a "mushroom" with a couple mm of "stem" showing ) and it fixed the problem.
    BMWs in my garage: 1982 R65LS, 1978 R100/7

  8. #38
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    The vent was operating properly. Must just be the angle of the picture that makes it look like you described.
    Thanks,
    Jim

  9. #39
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    Finally got around to opening up the rear drive and sure enough, no baffle. Took a few weeks for the part to arrive from Germany but it is in there now. I'll leave my sump line attached until i take it out for a spin this spring and confirm that this was indeed the issue.
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    Jim O'Coin

  10. #40
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    Good job figuring that out. Weird problem.

    Barron

  11. #41
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    Can you help me understand?

    Why did this just start up? It did't have the shroud before this summer. Why didn't it spew oil out before this? What changed?

    With the shield in place now, has it done any oil spewing at all?
    "The difference between death and taxes is that death doesn't change every time congress meets." - Will Rogers

  12. #42
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    I don't know why it didn't spew oil this badly in the past. The final drive vent plug was always wet with oil and occasionally there would be enough that i'd get a few drips of oil on the tire. All i can think of is that this slow progression of oil leakage would eventually lower the amount of oil in the final drive so that it wouldn't spew out during prolong travel at highway speed. The most recent occurrences were just after i changed the final drive oil so it had the full level at the time.

    Right now the bike is still in pieces so when i get it back together i'm hoping this solves my problem. Based on the number of folks that "never had this happen" I think i will be ok now that the baffle is in there.
    Jim O'Coin

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