Cable housing too short? That would be my first question.

Could be, but Tom's guys built that bike doubt if they would have missed it.

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Jim

**Note above poster works for a retailer selling bikes and related gear*

Well, I would diagnose it from simplest to easiest:

1. Is your rear wheel in straight? Did it shift during transport/loading?
2. Is there a stiff link? (Not too likely, I looked at your delivery checklist and we did check and sign off on the drivetrain).
3. As another poster here pointed out- trace the cable housing to see if there may be a break, kink, bend, etc.

I hope it isn;t something we missed... That is (honestly) very rare and would be pretty embarrassing. Then again, we are only human too.

One way or another- this is the stuff I loose sleep over. If it is not a shifted rear wheel in transit please bring it back in here for us to look at. We'll gladly compensate you for your travel with some free stuff.

Let me know what you find out,

Tom.

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Tom Demerly
The Tri Shop.com

I wish you owned a shop in the bay area!

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"your horse is too high" - tigerchik

My Prodigy does this all the time (both big and small chainring) and didn't start until late last fall, only occasionally, but now it does it all the time. My LBS has done and checked everything, but nothing has fixed it. They suggest taking it back up to Davis to the shop I got it at and have them check the shifter and that it may be something in there and still under Shimano's warranty.

clm

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clm
Nashville, TN
https://twitter.com/ironclm | http://ironclm.typepad.com

are you running Microsoft on your prodigy?

I guess that would be the only case bike components could have unexpected behavior :-)

I had a similar problem with a Mavic wheel. The cups holding the wheel were loose allowing the wheel to shift back and forth on the axle.

Bryan

I had this problem - I bailed on my ride today because I was unable to go up hills without the bike shifting on it's own between three different gears. Turned out that in my rush to put my cassette on, I got one of the spacers switched - doh!

Tom, the wheel appears to be straight and I couldn't find anything wrong with the cables. It only did it the one time so far, will get back with you if I continue to have a problem. It was just a little unnerving to have it shift like that.

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Jim

**Note above poster works for a retailer selling bikes and related gear*

this probably isn't it, but figured i'd throw it out there:

check the teeth on your chainrings and cassette. see if any are abnormally bent or warped or worn. Stamped chain rings will have some variation to them, but usually you can recognize ones that are damaged. Teeth that are warped can throw the chain and cuase "ghost shifts".

I broke a chain mtb'ing just the other day as a result of this. "Ghost shifting" is not a problem to be ignored, chains are really not that hard to break if you are cranking a big gear uphill and it takes hard a jump down the cassette.

Realistically Jim, that shouldn't happen even once. I'd really like to be able to look at it if possible/convenient.

We use either PG2000 or T-9 Boeshield on the drivetrains before they leave the store and we are actually backpedalling the chain through a towel to remove the excess lube on the chain. If there were a stiff link it genrally shows up then, although the occasional one could get through I suppose. That is what kind of worries me here.

Have you tried pedalling backwards and watching the chain go back through the derailleur? It should transition across the pulleys (jockey wheels) smoothly. If you see a little "kick" in them- boom- probably a stiff link. That might prompt the chain to jump from one cog to another.

The irony of this is that, although this is a MAJOR annoyance for the person riding the bike (even if it only happened once, it is like you are waiting for it to happen again...) it usually amounts to a somewhat minor adjustment to correct it.

Let me know what you find out and what we can do for you.

Tom.

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Tom Demerly
The Tri Shop.com

Tom. I really appreciate your concern in this manner. I will keep an eye on it and will bring the bike with me on my next visit to the shop. that will be when you get all the wetsuits for the season in.

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Jim

**Note above poster works for a retailer selling bikes and related gear*

Remember the simplest explanation is usually the right one, check the following

1) Cable tension is wrong, (more than likely). You can tell by shifting to the 4th position, the derailleur should line up exactly underneath the 4th (ie middle) cog. when backpedalling a stationary bike, there should be no tendency to shift gears

2) derailleur hanger is bent

3) cassette / chain is worn out.

4) freehub body is loose and / or cassette is not properly tightened.

5) too much drag in cables, preventing the derailleur from moving properly.

If none of those things, write back and let us know wnat was really wrong.

Oh yeah, the Dual has internal cables, right. It is possible for shift cables to be accidentally crossed inside the frame. If that happens, shifting the front derailleur will affect the tension on the rear derailleur cable. You can tell by shifting the front chainring and observing the rear derailleur, to see if it moves. The shop may not notice somehting like this before it leaces the shop.

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