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Help, chain overshifting on the tandem(6 posts)

Help, chain overshifting on the tandemMel Erickson
Apr 11, 2002 7:07 PM
I've got a Santana Rio tandem with an overshifting problem. The chain shifts off the small chainring when your torqueing up a hill and shifting from the middle to small ring. This only happens under torque. The travel is set properly, the derailleur almost touches the chain when in the small/big combo. The crank is an Aeromax with an XTR FD M900 front derailleur (top swing). Rear is XT, with an 11-30, 8spd cassette. It's dumped several times and has really scratched up the chain stay where it joins the BB. This has got to end. Temporarily I'm considering a chain keeper but I'd rather have a real fix.
re: I suspect this is stuff you know already, butdzrider
Apr 12, 2002 4:33 AM
Be certain that the derailleur is no higher than it needs to be for the outside of the cage to clear the large chain ring.

If the derailleur clamps on, you can check that the cage runs parallel to the chain. If it is you may want to try pivoting the derailleur very slightly so the back end of it is a little further out from the stay. This may cause it to go off the big ring, but that's less harmful.

On our tandem, I was never able to get a Suntour XC Pro front derailleur to work and wound up using a Shimano Deore that came on a bike with half-step plus a granny gearing. I don't know why but it seemed to handle the wide range of the tandem's chain rings very easily.

Until you find a solution shift first, torque later.
We run a chain keeper on our tandem.MB1
Apr 12, 2002 4:39 AM
Most teams around here seem to. I believe Santana has included it on their tandems for a while.

I think the problem is that it is tough to shift on a tandem. Getting 2 riders to ease up just enough but not too much is not an easy thing.

the chain keeper is an easy fix, give Santana a call for the correct size.
Chain keeperSpoke Wrench
Apr 12, 2002 4:57 AM
The newer Santana tandems come stock with a chain keeper installed, so this must be a fairly common problem. The bad news is that I don't think it's going to fit with your top swing derailleur. Do you have room to install a traditional geometry front derailleur?

I'm a little surprised that you are having this problem with an XTR front derailleur. Most of the bikes I have worked with that intermittantly threw the chain had 105 front derailleurs. It seems like the derailleur binds up a bit and then "throws" the chain hard enough that the momentum carries it over the granny.
Small ring spacersharry hall
Apr 12, 2002 6:14 AM
2 things: Use the thickest possible spacers between the small chainring and the crankarm--this will move the small ring closer to where the chain wants to land. My Ibis works fine with a 28/44/54 with 4.5mm thick spacers between the 28 and the arm. Second thing, and this goes against fashion, but TANDEMS SHOULD ALWAYS HAVE A FRICTION FRONT SHIFTER because of the need to exercise finer control over front downshifts than the slap-bang of STI or Rapidfire will allow. The use of indexed front shifting is without a doubt why Santana includes chain-catchers on their bikes!
Good tips all, thanks alotMel Erickson
Apr 12, 2002 8:08 AM
Unfortunately the LBS don't have a chainkeeper in stock and I don't have time before my ride tomorrow to delve into the chainring spacers. I'll just have to "shift early, shift often" and be careful. The friction shifter for the frt. der. sounds like a good idea. Since this is a mountain tandem I can probably use an old friction thumb shifter I have laying around in the parts bin. Maybe I'll try that tonight. 80 miles tomorrow. Here in west central Wisconsin the starting temp should be 40 with a high of 55 and partly cloudy skies with light winds. Sounds like a marvelous day to be alive.