warren goodwine

My friends have a Cannondale Tandem and it will shift on its own when they are climbing. Could this be due to frame flex and deraileur adjustment ? Or what ? Any imput would be appreciated

Possum Roadkill

The upper pulley wheel on Shimano deraileurs has some float in it to adjust for a little bit of inconsistency, like frame flex, however if the deraileur is adjusted right near the limit, it can move to the point that it causes a shift while climbing, so I would check the adjustment. I'd also look at the possibility of a loose cassette being the problem. Make sure the lockring holding the rear gears is thorougly tightened. If the cassette is old and has had several chains, it may skip due to the teeth no longer matching the pitch of the chain. I'd at least take a look at the cable routing to make sure nothing is holding up the cable anywhere either.

MB1

Their tandem is HAUNTED!

More likely it just needs some servicing including lubing the cables or replacing the cables and housing.

TandemGeek

"Shifting on its own" is pretty vague; shifting up, shifting down, or is it simply chain slippage?

Assuming it's actually 'autoshifting' and as some have already noted, if the derailleur isn't properly adjusted some jumping could occur.

However, if the shifting can't be 'dialed-in' using the barrel adjusters on the derailleur or front cable stops, one other thing to look for is a loose or bent derailleur hangar. Cannondale, like most aluminum frame builders, uses a replaceable derailleur hanger. If their tandem fell on the right side, or if the rear derailleur got banged up against something it may have been bent inward just a bit and/or gotten loose. For various reasons, a slight bend in the rear derailleur hanger will often times go unnoticed except during hard climbing efforts. A good bike shop will have a derailleur alignment tool that can be used to check this and, assuming it's just a little off, put it back into proper alignment.

specbill

Cables...cable housing....

Bill J.