My 15 year old Roberts touring bike had the chain start jumping on the
big chainring but not on the middle chainring. Big chainring was
shark-toothed and incidentally so was middle chainring. (Campag ATB
Record).
I've just fitted new TA Campag-pattern middle and big ring (last night,
fiddly job having to also unbolt the little chainring allen-bolts too).
Chain and sprockets have been replaced over the years a few times.
But even with new chainrings, it still slips horribly on the big
chainring if I push down hard on the pedals, yet is well-behaved on the
middle chainring.
I suspect the rear Campag mech has a broken spring or summat...is there
a diagram anywhere of what a Campag Record rear mech should look like,
components-wise.
It is making a "tick-tick" noise and flicking slightly forwards with
each tick too, which it didn't used to do. Hence why I suspect a spring
has broken so it's not able to tension big gears (big ring) only medium
and small gears (middle ring and, if I were to find a 1-in-5 hill, small
ring).
The chainrings needed replacing anyway.
Cheers,