Shimano SLX 12 speed crankset confusion- Mtbr.com
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  1. #1
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    Shimano SLX 12 speed crankset confusion

    I have a Boost frame with a 73mm threaded bottom bracket. The frame is Boost so I ordered what I thought was the Shimano SLX 12 speed Boost crankset (7120)

    When installed according to instructions the non drive side crank arm does not completely slide onto the spindle. Everything holds but unlike other Shimano cranksets it is clearly not fully onto the spindle shaft. I did use the two 3mm spacers they say to use between the crank arm and the bottom bracket (one on each side)

    I noticed on my new Giant Anthem that the SLX 12 speed crankset they used is the 7100. Is this what I should have bought for my other bike. Is this the issue.

    Would welcome any thoughts you may have on this.

  2. #2
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    I got the same cranckset to use on my Sentinel, but only needed to use one spindle spacer. The Sentinel is also a Boost frame with 73mm BSA BB shell. The M7120 is more geared toward boost frames because of the chain stay clearance of some boost frames that can't take bigger chainrings without touching the chain stay.
    If you don't have problems with wider Q-factor and want/need more chain stay clearance, the M7120 was the right choice.

  3. #3
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    One spacer for 73mm and three for 68mm. From the Shimano Dealer Manual, including but not limited to the 7120. Boost is just about chainring position (chainline) AFAIK.

    Shimano SLX 12 speed crankset confusion-7120-spacers.jpg
    :nono: :thumbsup:

  4. #4
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    It's not that spacers, the new direct mount cranckset style has spindle spacers to help take the slack if needed.

  5. #5
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    Quote Originally Posted by Aglo View Post
    It's not that spacers, the new direct mount cranckset style has spindle spacers to help take the slack if needed.
    Oh, I see. Well I learned something today.
    :nono: :thumbsup:

  6. #6
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    Quote Originally Posted by Aglo View Post
    It's not that spacers, the new direct mount cranckset style has spindle spacers to help take the slack if needed.
    Thanks for the replies.

    What I am trying to figure out is the use of the spindle spacers. I am using one on each side like they say to but it does not seem right. Anyone else have this experience?

  7. #7
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    Whoís side did you use the spindle spacer on, Drive or non Drive side?

  8. #8
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    Two of the spacers are intended to make up the difference in width between 68 and 73mm BB shells. (73-68)/2=2.5mm. So these arenít used with a 73mm shell.

    The third spacer will typically go on the DS because it is meant to take up the space that a sandwiched ISCG mount would typically take up.

    With Shimano cranks, the chainline dimension is built into the crankset itself.


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  9. #9
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    Quote Originally Posted by incubus View Post
    Two of the spacers are intended to make up the difference in width between 68 and 73mm BB shells. (73-68)/2=2.5mm. So these arenít used with a 73mm shell.

    The third spacer will typically go on the DS because it is meant to take up the space that a sandwiched ISCG mount would typically take up.

    With Shimano cranks, the chainline dimension is built into the crankset itself.


    Sent from my iPhone using Tapatalk
    I think you are referring to the bottom bracket. I have one spacer on the drive side for that. What I am referring to is the spacers that are now included with the Shimano 12 speed cranksets. These are meant to go on the spindle but the information is unclear and I think may be wrong.

  10. #10
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    Quote Originally Posted by Ranger Pride View Post
    Whoís side did you use the spindle spacer on, Drive or non Drive side?
    I installed it on the NDS (left) as per Shimano's instructions. Only if you have clearance problems with frame and chainrings you should install it on the DS (right).

  11. #11
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    Quote Originally Posted by Ranger Pride View Post
    I think you are referring to the bottom bracket. I have one spacer on the drive side for that. What I am referring to is the spacers that are now included with the Shimano 12 speed cranksets. These are meant to go on the spindle but the information is unclear and I think may be wrong.
    Sorry, I saw the diagram that noapathy posted and made some assumptions. Should have read further.

    That said, if your BB is spaced too wide by there being too many spacers, then youe crank spindle wonít have enough penetration on the NDS side.

    If you donít run the crank spindle spacers, you might find that your crank fixing bolt bottoms out on the spindle allowing for some lateral movement of the crank.

    If you choose to run only one, Iíd let the chain line determine whether it goes on the DS or the NDS.

    I run an M8130 (superboost) crank on a frame with a 73mm shell. That unit has meaty spindle spacers. Not the most elegant solution IMO.


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  12. #12
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    Why don't you just remove one of the spindle spacers? If the arms clear the frame fine it doesn't matter. The difference between boost and non boost is the offset of the chainring. Spindle length is the same.

    I just installed a new slx 7120 crank on a 73mm BB frame with a 10 year old shimano BB. Cranks didn't come with any spindle spacers but with one BB spacer as shown in the diagram below everything fits perfectly.

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