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Sram GXP BB issue

SkonkSkonk Posts: 364
edited March 2012 in MTB workshop & tech
Hi

Bit of a hard one to explain this so bear with me....

I have an issue with a SRAM/Truvativ GXP BB which came installed on my 2011 StumpJumper Elite.

The crank recently developed some play and creakiness so I whipped it off to take a look and it seems that when installed as per the instruction manual (and how was installed as it came from the shop) there is a gap between the drive side cup and the crank arm (so the crank doesn't sit flush against the BB cup); It's a 73mm shell and the manual states no spacers for this size.

Since on the drive side the dirt cover (that goes over the bearings) is also a shim that goes into the inner race and is then trapped between the inner race and spindle, this gap creates space for the shim to work its way out and allow play in the crank because it's only about half way in and there are some cutouts in the plastic.

Looking at the wear on both the inner race and the plastic shim, it seems the shim has only been half way in for most of its life, which surely can't be right? since this not only allows it to wobble but means that crud and stuff is able to get to the bearings.

It seems to me that it needs about 4 or 5 mm of spacers somewhere, to close the gap between the drive side crank and the cup so the shim is actually held in place but since the manual says not to use any spacers I don’t really know what to do.

Thing is, I've seen this same problem on a friends bike (totally different brand of bike, shop bought and all standard) and in the end, after going back and forth to the shop and the shop seemingly just pushing the shim back in and claiming it was fixed (only for it to just pop back out) he just stuffed a load of spacers on to try to fix it.

Any advice?

(I’ve attached some diagrams)

Thanks.
Canyon Spectral AL 9.0 EX
Planet X RT90 Ultegra Di2

Posts

  • supersonicsupersonic Posts: 82,708 Lives Here
    I have had quite a few problems with GXP and a Noir crank: I run 68mm shell, and received the crank on a bike with no spacers. I added two 2.5mm spacers, and had to torque the single bolt very high to remove play.

    It seems there are two GXP set ups, one that uses spacers, one that does not.

    My crank appeared to have some sort of spacer attached to the spider though!
  • bennett_346bennett_346 Posts: 5,029
    All the GXP BBs ive had have had this part you mention sit where yours does (ie wrong). It's just a censored design. I took it off as it always worked its way out thus served no purpose.
  • nicklousenicklouse Posts: 50,675 Lives Here
    Yes there should be a gap as the bearings do not run any preload.

    Yes the cap can be removed to allow you to grease the bearings.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • SkonkSkonk Posts: 364
    Thanks for the replies chaps.
    nicklouse wrote:
    Yes there should be a gap as the bearings do not run any preload.

    Yes the cap can be removed to allow you to grease the bearings.

    It's not a case it being removed though, it's the fact that it's removing it's self.

    The shim sits between the spindle and inner race of the bearing, if it's not in then there is a gap between the spindle and the inner race so the crank develops play (and is probably why for the last 2 weeks i've had a load of pain in my right knee).

    The shim/cover is naturally working it's way out and ending up pressed tightly against the crank arm, leaving the bearings exposed (4 or 5mm gap) to dirt and the crank free to wobble about, if I push the shim back in by hand it will be ok for a few minutes of riding then just do it again.

    So I understand that this setup doesn't preload the bearings but it can't be right that the gap allows the shim/cover to pop out and for the crank arm to wobble about even when it's torqued up to the correct values (which is it).

    But from the other replies it does suggest to me that I need to look for a shimano crank set or demand the shop take it back and give me a refund (it's 4 or 5 months old).

    James.
    Canyon Spectral AL 9.0 EX
    Planet X RT90 Ultegra Di2
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