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Old 01-01-06, 07:21 AM   #1
netorius77
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XTR/Crossmax slipping chain

Someone - please help me. I purchased a second hand 2003 Giant NRS Air with full Shimano XTR components, and Mavic Crossmax wheels. I have had nothing but grief with this surposedly pretty high end setup. I am reasonably mechanically minded, but this has me stumped. I have read through numerous posts on the subject with no definitive answer.

It started off with having to get the front middle chainring replaced as the original one was damaged/bent. That done, they changed the chain and rear cluster at the same time. I could now ride on the middle chain ring, but on a down hill, the chain somehow got caught against the tyre. I sent it back but apparently there was some problem with the Crossmax freewheel hub which they serviced and seems to be resolved although if you are peddling fast on a downhill in a high gear and stop abruptly, it does tend to catch - I can live with this.

Now my major, so far unresolvable, problem. When ever I am climbing a steep hill in a lowish gear, I seem to get some kind of slipping of the chain (or possibly free wheel hub). It doesn't move out of the selected gear, just "slips" what feels like a tooth or so every pedal rotation or so. I cannot work out exactly where it is slipping, but pretty sure it is at the back and not on the chain ring. It is ususally middle chain ring, and second or third gear at the back when this occurs, and under considerable load (climbing).

It really has me stumped. Being a full suspension bike I thought it may be flex in the frame/swingarm, but this doesn't seem to be an issue at all as all the bushings/ bearings are tight with no perceivable play.
My chain ring is an XTR P-46/34/24 with an HG53 chain and a 34/30/26/23/20/17/15/13/11 rear cluster. As stated the rear wheel is a Mavic Crossmax including the freewheel hub. General no load shifting is fine. I have tried to simulate the problem on a bike stand with no success. How do I access where the problem lies?

Any suggestions would be greatly appreciated.
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Old 01-01-06, 11:21 AM   #2
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That sounds like a stiff or twisted chain link. Or you have a damaged freehub.
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Old 01-01-06, 03:35 PM   #3
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I have had a couple of those bikes that had similiar problems but it always worked out to be a problem with frame flex/rear suspension movement causing the cable housing to pull on the cable and make it shift. We ended up running the rear der. cable at it's loosest possible point that still shifted well.
Ever since the first time I took a mavic x-max freehub apart I have disliked that whole design and I've seen plenty of problems with them since.
I know that you say you elimninated both these factors as a possible cause but I would take another look. One way to eliminate the wheel as the suspect is to try a different one on the NRS that is functioning properly. While you're at it test the mavic wheel on a different bike that was running properly. Try both, swapping the cassette onto the other wheel, and keeping the cassette with it. I wouldn't eliminate the possibility that it is a combination of the Mavic wheel with the NRS frame either.
I know how frustrating this can be, hope you get it worked out.
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Old 01-01-06, 03:52 PM   #4
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You might want to check your chainline. If you're too far angled in you can sometimes catch against your tyre... especially when the swingarm is compressed. If your BB doesn't have an adjustable chainline capability then you might want to consider getting one that does. This might also be the cause of your slipping problem.
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Old 01-01-06, 05:19 PM   #5
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You can always take it by your local bike shop and have them take a look at the cassette with a cog pitch checker tool.
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Old 01-01-06, 05:21 PM   #6
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^^ Here's the tool I'm talking about: http://www.wiggle.co.uk/ProductDetai...9582&UberCat=0

Edit: Found it at a USA site http://www.cambriabike.com/shopexd.asp?id=13754
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Old 01-01-06, 09:05 PM   #7
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Thanks for all the advice. I guess my easiest starting point is to borrow another wheel and see if it does the same thing. That way I can eliminate (or isolate) the freewheel/casette issue.

Regarding the chainline suggestion, how does one know where the chain should be running. Is the a recommended setting?

I tend to agree about Crossmax issue. I have had all sorts of problems. My recommendation - stick to conventional wheel sets!
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Old 01-01-06, 09:15 PM   #8
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Quote:
Originally Posted by netorius77
Regarding the chainline suggestion, how does one know where the chain should be running. Is the a recommended setting?
For full-suspension bikes this can depend on the frame. The manufacturer might have some specs.
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Old 04-30-07, 06:28 PM   #9
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What year is the NRS?
If the frame is still under warranty, you could sweet talk the person you bought the bike from to help out in getting it fixed.
Also, I hate so say it, but do you think you may have bought somone elses problem?

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