U-joints; Twin Shock vs Paralever

Discussion in 'Airheads' started by Big Bamboo, Apr 29, 2013.

  1. Big Bamboo

    Big Bamboo Aircooled & Sunbaked

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    I know the twin shock BMWs require a bit of gear oil in the swingarm, but the Paralevers do not. Are their U-joints of a fundamentally different design, such that a Paralever is lubricated for life? Or is the oil there primarily to lubricate the splines where the shaft mates to the rear drive? (done with grease on the Paralever)
    #1
  2. Boxer Metal

    Boxer Metal Mad Scientist

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    The u-joints are the same on pretty much all BMW's produced after 1970, minus the new new bikes. The oil in the early bikes did more for the splined end at the rear drive.
    #2
  3. More_Miles

    More_Miles ├╝ber-n00b

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    While I don't disagree about being mostly for spline lubrication, I think there is more than a little oiling going on at the U-joint on the twin-shock models. I base this solely on the personal and anecdotal observation that I've never removed the rubber boot at the transmission output without having to dump a tablespoon or so of oil out of it. It had to get there somehow, and once there, probably provides some splash lubrication with bumps, jolts, etc. In my opinion, any lubrication in this application, even accidental (at least in a closed system like a twin shock swing arm anyway) is better than none.

    The description "lubricated for life" is accurate. Bearings, joints and the like usually die through lack of lubrication. I'm sufficiently old-school to still want grease fittings on U-joints, ball joints, and bearing oilers where appropriate.
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  4. ME 109

    ME 109 Long timer

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    What about the dust seals on uni joints?
    They probably prevent any significant amount of oil from getting into the needle rollers.
    I cant remember what the oe uni joint looks like, but the Hardy Spicer unit I used as a replacement on my RS had dust seals on it. As far as I can remember, I didn't take them off and that was a long time ago.
    #4
  5. Solo Lobo

    Solo Lobo airhead or nothing

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    Here's a shot of the joint on my R80G/S.. the factory one being replaced by an HPMGuy replaceable one...

    [​IMG]
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  6. Boxer Metal

    Boxer Metal Mad Scientist

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    Here is a driveshaft I built for one of my projects. Part /6 and part R1150 showing the u-joints are all the same. With that said the paralever models do not have oil in the housing and the u-joints last just as long as the earlier models.

    [​IMG]
    #6
  7. ME 109

    ME 109 Long timer

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    Interesting, half circlip and half welded washer.
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  8. Stagehand

    Stagehand Imperfectionist

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    welded washers hold the circlips in :deal
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  9. ME 109

    ME 109 Long timer

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    So what's with the shaft in the pic, only two washers?
    Washer and circlip doesn't make much sense to me, either way should be good on its own.
    #9
  10. Stagehand

    Stagehand Imperfectionist

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    Sorry- to retrofit the circlips onto the shaft, where the cardans were originally staked in, washers need to be welded onto all four apertures. They become the de-facto "hold the circlips in" devices. Without the washers which are not longer washers in this application, but have become forward material to bear against the outer surface of the circlip, you would have to somehow grind a trough out of the yoke material for the circlip to ride in to hold the cardan in.
    There probly isnt enough material there to do that job, even if you could grind an interior radius like that, so you weld a washer on top, and the space between becomes the shelf where the circlips ride.

    Clear as mud, eh? :lol
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  11. ME 109

    ME 109 Long timer

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    I just used washers, although a belt and suspender approach can't hurt.

    [​IMG]
    #11
  12. Stagehand

    Stagehand Imperfectionist

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    Well the whole point of circlips is that theyre replaceable ie rebuildable without future grinding and welding

    Like putting clips on your suspenders and not sewing your belt to your pants :)
    #12
  13. mattcfish

    mattcfish R90X

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    Anybody have a part # for the u joint on a 70 to 80's airhead? Can you get them through Spicer? Not readily available anywhere I've checked. I've got a shaft I need to rehabilitate. I like ME 109's DIY method. Probably quicker to grind off the 2 spot welds than to remove a fiddly circlip. Should last another 100,000 miles anyway.

    To answer the question about oil getting to the u-joint. When you go down hill lots of oil gets to the front of the shaft. You'll find this out if you ever get a split in the rubber boot.
    #13
  14. ME 109

    ME 109 Long timer

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    The hardie spicer uni cost me about 175 delivered. Bloody expensive! I got caught out because I didn't ask for a price..........because I didn't recall it being so expensive 15 years ago when I last repaired the driveshaft uni.

    There will be other brands for a lot less. Just need to cross reference the size.

    I can measure my old uni when I get home, unless someone else knows?
    #14
  15. RecycledRS

    RecycledRS Along for the ride

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    Got a part number? Failing that dimentions would be appreciated.
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  16. _cy_

    _cy_ Long timer

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    there is NO way non serviceable ujoints with no way to add grease like used in all paralever last long as earlier ujoints bathed in oil.

    all bearings require lubrication to prevent metal to metal contact. when grease in those tiny ujoints goes dry ... game over. they self destruct shortly after going dry. which is exact what BMW wants.

    major components that last for lifetime of the bike is NOT good for new bike sales. IMHO this is why BMW moved away from taper roller bearing used in airheads. because airhead wheel bearings typically last lifetime of the bike.

    BMW knows how to design components to last lifetime of the bike. look no further than monolever final drives which typically last the lifetime of the bike.

    compare that vs R1200 final drives which are notorious for failing. if one looks at design BMW went to a sealed main wheel bearing. this means main rear wheel bearing cannot be lubed by hypoid oils in final drive.

    BMW can control how long final drive bearing lasts by simply changing amount of grease main wheel bearing is loaded with and/or side pressure on bearing set by shims. have a final drive go out in the middle of a long road trip could mean costs to repair approach 1/3 to 1/2 value of motorcycle.

    it has gotten so expensive to repair late model BMW that it makes more sense to sell your BMW when it gets close to warranty. then purchase a new BMW with warranty intact. recent record sales for BMW Motorrad means their strategy must be working ...
    #16