Bicycle Mechanics - Smallest cog slipping

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cooleric1234
08-12-10, 09:36 PM
My wife borrowed a bike from someone recently and I'd like to tune it up a bit before giving it back to them. One problem that already existed with the bike before my wife got it was to do with the smallest cog on the cassette. Whenever in that gear sometimes it feels like the cassette slips. I'm not sure how to describe it, but my wife will be pedaling and her feet will still go around but it's like it won't propel or turn the wheel any more.

At first I thought it was a problem with the frame and cassette. You'll notice by the attached photo that the smallest cog is right up next to the frame. I thought that maybe the chain runs up on the frame and loses grip with the cassette. I'm not sure that's the case though, in that case I would think it would stop altogether and grip.

One other thing worth mentioning is that I tried to remove the rear wheel and I couldn't. It felt like it was stuck in there. I've done it tons of times on my bike, I don't know if I'm doing something wrong, but it's not rocket science. I loosen the QR skewer but then I can't force the wheel out. Any ideas?

164502

ramjet1953
08-12-10, 10:36 PM
Yes, that top gear certainly seems very close to the frame.

If I read what you say correctly, there is a total loss of drive, not just the chain jumping?
If this is the case it would be worthwhile to remove the cassette from the freehub body and check the splines on the freehub body. It sounds like they may be stripped right at the end where the high gear sits.

From the photo it looks like a Shimano setup, so you will a Shimano cassette tool and a chainwhip to remove the cassette,

Regards,
Roger
cooleric1234
08-12-10, 10:39 PM
Yes, that top gear certainly seems very close to the frame.

If I read what you say correctly, there is a total loss of drive, not just the chain jumping?
If this is the case it would be worthwhile to remove the cassette from the freehub body and check the splines on the freehub body. It sounds like they may be stripped right at the end where the high gear sits.

From the photo it looks like a Shimano setup, so you will a Shimano cassette tool and a chainwhip to remove the cassette,

Regards,
Roger

Thanks. Yes, it's a total loss of drive but it comes back. I would say it slips for half a revolution then grips for a little bit, then slips again. I was wondering about the splines, just forgot the term :-) I suppose the only solution to that is a new freehub? Could I add a spacer or something on the end of the cassette to increase clearance?

ramjet1953
08-13-10, 03:12 AM
OK, if you need to replace the freehub body, you will need a large allen key to do so.
Here's a linlk explaining how to do so:

http://www.sheldonbrown.com/k7.html

Depending upon the manufacturer of the freehub you will need an 11, 12, or even 13mm allen key.

With the chain being very close to the frame, you would need to adjust what is called the overlocknut dimension of your rear axle.
The most common dimension for modern dérailleur bicycles is 135mm for a mountain bike and 130mm for a 10 speed road bike.
Here is an excellent link with pictures to explain how to do this:

http://www.sheldonbrown.com/chainline.html

Regards,
Roger
mcgreivey
08-13-10, 07:53 AM
Seems like maybe the bike has a non-original wheel with wider spacing than the frame, and that's why you're having trouble getting the wheel out, and that's why the small cog is so close to the dropout. Is that causing the "slippage" problem? I don't know... Yes, maybe the freehub is failing. Perhaps it's happening because of the spacing issue? Stress on the axle?