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  1. #1
    cyclist/gearhead/cycli... moxfyre's Avatar
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    New (to me) SRAM force cranks wobble... BB problem?

    Hi all, I bought a moderately used 2007 SRAM Force group and installed it recently on my road bike. Everything works great, except for the cranks. There's an unusually large amount of side-to-side play in them. They're clearly not pressed all the way up against the bearing surfaces.

    I've never installed external bearing cranks before, but not exactly sure what I did wrong. I followed Park Tool's instructions. The BB cups seemed to install just fine in my 68mm BB shell.

    I installed the right crank, then the splined left crank, and tightened it down as far as it would go. I tightened the bolt that attached the splined left crank almost to the point that I was afraid of stripping it, but there's still a lot of wobble in it.

    I'm trying to figure out what could be wrong. The spindle appears to be straight and undamaged.

    1) My BB shell is not wide enough. Spacers needed? Park Tool says these aren't needed for SRAM force. And the old Shimano Octalink BB fit fine...

    2) BB bearings are completely hosed and flex all over the place. They don't look brand new, but turn smoothly by hand, so I doubt this.

    3) There's something else preventing the spindle from pressing all the way up against the cartridge bearing surfaces. What?

    Has anyone else had this problem? Any advice will be greatly appreciated!
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  2. #2
    coprolite fietsbob's Avatar
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    spline interface doesn't need tightening , so much, You may have damaged the crankarm,
    or the last guy did and that's why he sold it.
    torque wrenches at least offer Data,, how much is a number.. that can be typed ..

  3. #3
    pmt
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    The right side simply rides on the bearing; it does not need to press against the cup. You probably have a loose spider-crankarm connection like this.

    The red line shows the motion possible, the yellow shows the gap created. That turned me off any Truvativ crank going forward, since I had an aluminum unit do the same thing.

    sram_crank2.jpg

  4. #4
    totally louche Bekologist's Avatar
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    Bring it into the shop, i think you might need a wavy washer at the very least!
    "Evidence, anecdote and methodology all support planning for roadway bike traffic."

  5. #5
    cyclist/gearhead/cycli... moxfyre's Avatar
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    Quote Originally Posted by fietsbob View Post
    spline interface doesn't need tightening , so much, You may have damaged the crankarm,
    or the last guy did and that's why he sold it.
    torque wrenches at least offer Data,, how much is a number.. that can be typed ..
    There doesn't appear to be any damage to the splines...

    Quote Originally Posted by pmt View Post
    The right side simply rides on the bearing; it does not need to press against the cup. You probably have a loose spider-crankarm connection like this.

    The red line shows the motion possible, the yellow shows the gap created. That turned me off any Truvativ crank going forward, since I had an aluminum unit do the same thing.
    Thanks, that picture was helpful. My right crankarm basically looks just like that, but the spindle interface is NOT loose. The play is definitely due to the cranks not pressing down on the bearings, even when tightened as much as possible.

    (And thanks for correcting me... I didn't mean that the right arm had to press against the cup, just against the bearing surface.

    Quote Originally Posted by Bekologist View Post
    Bring it into the shop, i think you might need a wavy washer at the very least!
    According to Park Tool, the SRAM cranks don't use wavy washers. But at this point, I really really think the spindle is too long or the BB shell is too narrow, for some reason. I believe I need a spacer of some kind. I'll take it in and see what they think. THanks!

    Oh, and glad to see you Pacific NW-ers in this thread. I'm moving to Portland, Oregon next week
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  6. #6
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    you are using a sram bb or a bb that is designed for the gxp system? the left cup has a spacer pressed in the bearing

  7. #7
    totally louche Bekologist's Avatar
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    sram tech docs show a spacer, wether it is attached to the bearing assembly is unclear. I'm not familiar with the crank and BB enough to say from experience.
    Last edited by Bekologist; 09-23-10 at 11:22 PM.
    "Evidence, anecdote and methodology all support planning for roadway bike traffic."

  8. #8
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    I think you need 2.5mm BB spacers on either side of the BB shell. The crank is probably made for a 73mm shell width.

  9. #9
    cyclist/gearhead/cycli... moxfyre's Avatar
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    Quote Originally Posted by reptilezs View Post
    you are using a sram bb or a bb that is designed for the gxp system? the left cup has a spacer pressed in the bearing
    Bingo. It was a Shimano BB... *sigh*

    The previous owner told me that the BB and crank had worked together, but obviously this was incorrect. The size of the Shimano and GXP BBs is really similar, but not exactly the same. Annoying
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  10. #10
    pmt
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    The only real difference is that the GXP has a reducing insert on the left side. A GXP crank will fit into a Shimano BB, but will never tighten properly. A Shimano crank won't fit all the way into a GXP BB unless the insert is pressed out. Then it works fine.

  11. #11
    cyclist/gearhead/cycli... moxfyre's Avatar
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    Quote Originally Posted by pmt View Post
    The only real difference is that the GXP has a reducing insert on the left side. A GXP crank will fit into a Shimano BB, but will never tighten properly. A Shimano crank won't fit all the way into a GXP BB unless the insert is pressed out. Then it works fine.
    Ah, that makes sense. See, I had noticed that the parts were different brands, but I figured that because the cranks just had to press up against the bearings, there would be little difference between the different brands. As you point out, the insert makes the whole difference, and its absence prevented the crank from tightening in the Shimano BB.
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