Bicycle Mechanics - Shimano XT Derailluer won't stay adjusted?

On my '06 Stumpy I've got the stock Shimano M-750 XT rear derailleur. I can adjust it but it doesn't seem to hold the adjustment for more than a week. Even when I get it pretty well adjusted it still will skip a gear when I really get on it.

I want a system that works well all the time that doesn't require constant adjustment. Does upgrading the derailleur system to something better make for shifting that is spot-on and reliable?

Thanks for any suggestions. I take this bike deep into the wilderness alone and really want something dependable.

Chuck

The M-750 is a solid derailleur. I've got them on my tour bike and my mountain bike. Are you sure your derailleur hanger is not bent?

You would be surprised at what can hang up even the best of derailleurs.

There is a multitude of things that should be looked at:
1) Loose cassette
2) Worn cassette and chain
3) Bad inner wire
4) Bad cable housing, kinked, worn, bad ferrule
5) Dirty Shifter

And these are just the start! My guess is a bad wire or housing.

Does upgrading the derailleur system to something better make for shifting that is spot-on and reliable?

There's nothing you can get that will be more "spot-on and reliable" than a Shimano XT RD. I think your problem lies elsewhere. As roadfix suggested, maybe a bent hanger. Also, full suspension bikes are particularly prone to ghost shifting if there's any problem at all with the derailleur cable-

You would be surprised at what can hang up even the best of derailleurs.

There is a multitude of things that should be looked at:
1) Loose cassette
2) Worn cassette and chain
3) Bad inner wire
4) Bad cable housing, kinked, worn, bad ferrule
5) Dirty Shifter

And these are just the start! My guess is a bad wire or housing.

Good list. Also check for a tight chain link, especially if the chain was installed/reinstalled right before your problems.

XT is a pretty solid der, and I have them on a 10 year old hard tail and 4 year old full suspension. I've had zero problems with the der itself.

You would be surprised at what can hang up even the best of derailleurs.

There is a multitude of things that should be looked at:
1) Loose cassette
2) Worn cassette and chain
3) Bad inner wire
4) Bad cable housing, kinked, worn, bad ferrule
5) Dirty Shifter

And these are just the start! My guess is a bad wire or housing.

I'm betting on #4 because I've encountered that several times. The thing to look for is one or two tiny wires sticking out of one of the cable stops. When that happens the cable housing is gradually shortening itself. You can adjust the cable tension and fix the shifting but you find yourself doing it frequently as the cable housing shortens.

I'll also add bent derailleur hanger and mis-installed wheel, as long as you're looking for culprits.

Thanks for the great inputs! I'll put it on the stand today and really go through it. I'll post when I find the culprit...

Chuck

Cable housing was the culprit with my bike recently. There were no obvious external signs of damage or wear to the housing, no rust or wires sticking out. I swapped it out because it had been on for a couple years and it was cheaper than replacing the derailleur or shifter. New housing made the problem disappear.

Well the forum was right! It was the cable housing. Slapped a new one on there and the whole thing works like a charm.

Thanks again for the help.

Chuck

I'd also doublecheck that you have 4mm derailler housing instead of 5mm housing.