Chain jumping out of big cog when climbing

Hi all,

I am riding an early 90s steel Serotta frame with a 8 spd Campy group with a
28 tooth big cog and downtube Campy friction shifters. I am having a
repeating issue that if I am in the big cog and small chain ring (ie.
climbing steep grade), the moment I choose / need to stand up in the pedals,
the chain and downtube friction shifter jump to the second cog position.

This only happens at the moment I choose to stand. If I remain seated, the
chain will remain in the big cog. Somehow, I think this is related to the
increase in torque (frame or wheel flex) when standing. I know there is
some additional flex happening when I stand because I can hear a faint
ticking of the derailer cage on the spokes when I'm standing that I don't
hear if I am sitting.

I don't know if it matters, but I can recreate the same while the bike is in
the repair stand. If the chain is on the big cog and I put a little bit of
additional tension on the shift cable coming from the friction lever with my
finger, the shift lever will and chain will move to the second cog position.

FWIW, I do have the center screw of the friction lever tightened down
securely.

Any help would be appreciated.

Thank you

Tim

Tim Graichen wrote:
Hi all,

I am riding an early 90s steel Serotta frame with a 8 spd Campy group with a
28 tooth big cog and downtube Campy friction shifters. I am having a
repeating issue that if I am in the big cog and small chain ring (ie.
climbing steep grade), the moment I choose / need to stand up in the pedals,
the chain and downtube friction shifter jump to the second cog position.

This only happens at the moment I choose to stand. If I remain seated, the
chain will remain in the big cog. Somehow, I think this is related to the
increase in torque (frame or wheel flex) when standing. I know there is
some additional flex happening when I stand because I can hear a faint
ticking of the derailer cage on the spokes when I'm standing that I don't
hear if I am sitting.

I don't know if it matters, but I can recreate the same while the bike is in
the repair stand. If the chain is on the big cog and I put a little bit of
additional tension on the shift cable coming from the friction lever with my
finger, the shift lever will and chain will move to the second cog position.

FWIW, I do have the center screw of the friction lever tightened down
securely.

Any help would be appreciated.

Thank you

Tim

Like ERGO levers, these shifters use shift springs just like the ones
in the LEFT ERGO lever...maybe one of them is busted or just worn
out...may need 2 or 3...went to the 3 spring type about 1995...If 3
spring and ya take them apart, note the direction of the shift disc as
it can be assembled 180 degrees wrong..not a problem with the 2 spring
version.

Tim Graichen Wrote:
Hi all,

I am riding an early 90s steel Serotta frame with a 8 spd Campy group
with a
28 tooth big cog and downtube Campy friction shifters. I am having a
repeating issue that if I am in the big cog and small chain ring (ie.
climbing steep grade), the moment I choose / need to stand up in the
pedals,
the chain and downtube friction shifter jump to the second cog
position.

This only happens at the moment I choose to stand. If I remain seated,
the
chain will remain in the big cog. Somehow, I think this is related to
the
increase in torque (frame or wheel flex) when standing. I know there
is
some additional flex happening when I stand because I can hear a faint
ticking of the derailer cage on the spokes when I'm standing that I
don't
hear if I am sitting.

I don't know if it matters, but I can recreate the same while the bike
is in
the repair stand. If the chain is on the big cog and I put a little
bit of
additional tension on the shift cable coming from the friction lever
with my
finger, the shift lever will and chain will move to the second cog
position.

FWIW, I do have the center screw of the friction lever tightened down
securely.

Any help would be appreciated.

Thank you

Tim
From Sheldon Brown's page on this topic:
"The usual cause of the problem, believe it or not, is the cable guide
that the derailer cable uses to get around the bottom bracket. As you
pedal the bike, the frame flexes from side to side. This causes the
gear cable to get tighter and looser with every other pedal stroke."
More details @
http://sheldonbrown.com/autoshift.html


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daveornee