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  1. #1
    Dug
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    XT Cranks keep loosening...suggestions?

    I'm running a set of XT M-752 cranks on the XT bottom bracket. All splined. This isn't the 2 piece M-760 integrated system.

    I can ride perhaps 8 miles, and feel the chain line start to deteriorate. A check of the crank bolts shows that they are very loose. I have cranked the bolts down as tight as I can get them, and this still happens. I haven't used a torque wrench - I bought the bits but not the wrench itself yet. At this point, the crankarm hasnít spun itself off and the splines are not damaged and are perfect.

    I weigh 200 lbs, and like all ss'ers, mash up the hills. On my geared road and mountain bikes, this has never happened and I'm running the same shimano splined system on each of those. Of course, I donít mash on those bikes the same way, and Iím wondering if Iím flexing these cranks to a point where they loosen. Or, Iím not doing something correct in the setup.

    Looking for people who have had the same problem and what was done to fix it. Thanks in advance.

    D

  2. #2
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    Well, the splined system doesn't creep up the way square taper cranks do, as I understand it the system should bottom-out solid so it really does sound as if the bolts are actually backing out but they should only do that if there's movement between the crank and spindle..


    Check your cranks for cracks around the spindle hole, any cracks down there can open up and allow the crank to move on the spindle which could back-out the bolt. Another option is that there's a poor match of tolerances and your crank is actually "loose" on the spindle and each time you cycle the cranks it slops a little bit and that backs out the bolt.

    Either way try some lock-tite on the threads to keep the bolts from loosening and use a torque wrench at least once to find out what the proper torque feels like for those bolts.

  3. #3
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    1) Use locktite
    2) Don't grease the spindle

    And see if that does the trick.
    Dude, where's my gears?

  4. #4
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    Proper torque is everything...

    Quote Originally Posted by Dug
    I can ride perhaps 8 miles, and feel the chain line start to deteriorate. A check of the crank bolts shows that they are very loose. I have cranked the bolts down as tight as I can get them, and this still happens. I haven't used a torque wrench - I bought the bits but not the wrench itself yet. At this point, the crankarm hasnít spun itself off and the splines are not damaged and are perfect.
    I've weighed as much as 240 with my now going on 4 year old LX splined. Proper torque is everything to keeping these cranks happy. 35 foot-pounds is a lot of force to lay down on a standard 8mm allen key.

    Spend the $20 on a Craftsman beam-type torque wrench and give it another go. My cranks are always greased, no LocTite, and don't give me an ounce of trouble.

  5. #5
    ballbuster
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    I had the same issue...

    ... and I fixed it with red loctite. I would not recommend anybody else use red, but I was desperate and that was all I had lying around. I've had good luck with it, so I kept on using it with no issues. I guess Red is for larger threaded parts, and I figured that the 10MM allen bolt is pretty big around the threads.

    My install:

    Clean the crud out of the BB threads
    Clean the crud out of the crank bolts
    lightly grease splines, being careful not to get any where the threads go
    big fat drop of red loctite in the BB threads
    install crank and tighten nice and schnuggg

    Works for me with no loosening.

  6. #6
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    Holy crap! There is a good place in this world for Red LocTite, but you might not have found it!

    The red is designed for "near permanent" installation, and is really more cyanoacrylate glue than anything else. The key thing about Red that alarms me about where you used it is that it's not supposed to release your part AT ALL, unless you heat it over 350f, which usually done with a Torch.

    I hope your repair worked, and works, out great! I'd caution anyone about using Red LocTite, though. The Blue and Green formulas can often achieve what you're after...

  7. #7
    ballbuster
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    No issues yet

    I hear ya,

    but i have had the cranks apart about 8-10 times since my first install to change out worn rings, cleaning, servicing lower pivot point, etc. and I have never had any difficulty getting the parts apart. None whatsoever. My understanding of the difference between (and this may be wrong) red/blue/green was the size of the gaps it would fill. the instructions I read on the little tube was to use a certain flavor with certain sized bolts.

  8. #8
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    This is XTR but...

    Quote Originally Posted by Dug
    I'm running a set of XT M-752 cranks on the XT bottom bracket. All splined. This isn't the 2 piece M-760 integrated system.
    I've been having the exact same problem with my XTR splined cranks. I brought them by the Shimano tent at Sea Otter and the guy there said I have the old-style crank bolts that are aluminum. Apparently the newer crank bolts are stainless steel and the threads bite a bit better than the aluminum ones. I'm gonna get some new crank bolts and see if that doesn't solve my problem.

    Could be that there's a similar issue with XT cranks...

    -Trevor

  9. #9
    theHeadlessThompsonGunner
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    Make sure your spider isn't bent. I either bent mine, or it came outta the box bent - one way or another, I couldn't get the chainline worth a damn. I never had my ring come loose, but play between spider-cog-ring-chain-etc could cause it, I 'spose. Shimano was really nice and replaced it for me.

    I also agree with the above, that proper torque is everything. I'm running a Lexan bashguard, and I know my bolts are tight enough when the Lexan around the bolts starts to spider-crack. I grease my bolts (not loctite), and have never had them come loose - it might be due to the extra friction between the bolts and the lexan (which makes them squeak on installation), and you might consider making a plexiglass or lexan bashguard. Good luck - S
    "I've courted brain damage like some courtesan of darkness."


    -The Good Doctor

  10. #10
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    I had this problem too...

    I had this problem with 2 different XTR cranks, the 952 series. I actually ruined the drive side crank on one set because the splines got destroyed on the crank arm and so had to buy another single crank arm. I couldnt get the answer from anyone but also asked the Shimano folks at Sea Otter in 2003. The answer that kept coming back was make sure to torque to proper specs.

    What did the trick for me was simply the proper torque. 35 lbs-ft is a lot of torque and best applied with the proper torque wrench as well. Once i did this I have no absolutely no problems with my set. I greased my splines too and did not apply anything to the crank bolt. XTR crank and bolt purchased in early 2002.

    I weigh 190 without anything on and so am around 200 outfitted to ride, and, I ride up a lot of hills here in So Cal with this setup on my full suspension rig.

    Regards,
    LocoMotoMan

  11. #11
    theHeadlessThompsonGunner
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    Quote Originally Posted by LocoMotoMan
    What did the trick for me was simply the proper torque. 35 lbs-ft is a lot of torque and best applied with the proper torque wrench as well.
    I think 350 lb-ft is what you mean, but yes - it's a lot of torque.
    "I've courted brain damage like some courtesan of darkness."


    -The Good Doctor

  12. #12
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    Quote Originally Posted by SDizzle
    I think 350 lb-ft is what you mean, but yes - it's a lot of torque.
    It really is 35 ft-lbs (actually, 36).

  13. #13
    theHeadlessThompsonGunner
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    Ooops - I was reading inch-lbs as ft-lbs, but am still surprised to see that ft-lbs damn near equal Nm. Per Shimano's LX manual (XT-752 is no longer online, but they're the same): 35 - 50 Nm (305 - 435 in. lbs.)

    Here's the link: http://bike.shimano.com/product_imag...FC_M571_SI.pdf

    How can ft.-lbs. be so close to Nm? Luckily, I've always been able to wrench away as hard as possible and have them stay in place, and still get them undone!
    "I've courted brain damage like some courtesan of darkness."


    -The Good Doctor

  14. #14
    ballbuster
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    dang...

    .... the driveshaft locking nuts that pinch my front wheel bearings together on my 96 GTi are speced at 125 ft/lbs.

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