I bought a GT avalanche 3.0 2005 recently, and within the first 30miles
I had trouble with the casette/chain.
It seems that when using any of the chainrings, and the higher sprockets
at the rear (smaller cogs) my chain climbs and drops a gear or so whenever
I put a little power in.
It's making it impossible to ride, as the chain just jumps up and down a
gear all the time.
I thought perhaps the chain was faulty/damaged so I replaced it with a
new 8 speed SRAM, which seemed to work fine for the first 2miles or so,
now I'm getting the beginnings of the same problem.
The bike was prebuilt except for the usual handlebar/pedal adjustments
etc out of the box.
From turning the cranks while on a stand, I can see that the chain is
almost making contact with the next cog (lower gear) every now and then
as it leaves the casette. (This is not because of the deraileur)
Might the casette have the spacers positioned incorrectly or be damaged
in some way? To my untrained eye, it looks undamaged.
# Gears: 24 speed Shimano XC-202 front and Acera rear derailleurs
# Shifters: Shimano ST-EF29 gear shifters
# Chainset: Suntour XCC-252 chainset with 42-32-22 teeth chainrings
(top view of rear derailleur in 8th gear)
I'm aware that you're not really supposed to use certain gears where the
chain is forced to bend, but this problem happens in a range of gears,
even where the chain is straight (largest front cog + smallest rear cog).
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Thread: Casette/chain problem