Classic & Vintage - bottom pully on rear derailleur jumping

so the chain jumps a bit on the lowest gear the problem seems to be happening on the bottom pulley

Any idea on what could be causing this? it only happens when it's in the lowest gear(the one closest to the spokes) it's a '85 campy Victory derailleur

Maybe the hanger is a little bit crooked - or possibly the stop isn't adjusted quite right.

or a slightly bent tooth or maybe a bent link?

If your cable tension is good and nothing is obviously broken, then the lower pully probably isn't tracking on the chainline. This is from the cage being twisted. Take an "English Wrench" and snug it down on the lower pulley bolt and bend it straight. or your derailleur hanger is bent, if you don't have the tool take it to a shop.

Or maybe a tight link in the chain.

happens in the cog closest to the spokes, therefore largest and pulleys are under the greatest load, if everything looks straight and in plane, I suggest repacking the pulleys, had the problem on a pair of Campagnolo units decades ago I got one to stop, had to replace the other, if one had a radial crack, that also can do it.

thanks guys, I have a spare der so maybe I'll sub that in to see if it's the hanger or der that's causing the problem, if it's the der I'll overhaul the pulleys if it's the hanger I'll bring it in to the shop, I'm fairly certain that it's not the chain, as it skips on every revolution of the lower pulley.

Thanks!!!

Or maybe a tight link in the chain.

+1.

I've run into this on two different bikes lately. I'd check the chain first. Put the bike on a stand (or somehow elevate the back wheel), get yourself on eye level with the chain, and slowly rotate the crank. When you get to the point where the chain jumps on the pulley, test the links in that area. Try to flex the links. If they don't flex freely, that will cause the chain to jump.

I'd try this before changing out the derailleur.

OK i found the problem, I guess I damaged the old Der when the bike fell, YAY!
so now I have a Campy Victory der with a broken part, it's the part that adjusts the angle that the der sits on the hangar, it's partially snapped off, any ideas where i can get a spare part? I had a spare Campy Triomphe der that's sitting in the victory's place and working way better than the Victory, but i'd like to revive the Victory if possible.

...it's the part that adjusts the angle that the der sits on the hangar, it's partially snapped off, any ideas where i can get a spare part? I had a spare Campy Triomphe der that's sitting in the victory's place and working way better than the Victory, but i'd like to revive the Victory if possible.

The "fixed" adjustable parallelogram angle adjustment + derailer stop. You're probably SOL on that one - I've tried myself. I think one fellow on eBay had some a few months ago (along with the sprung C-Record first-gen variant), if I recall right, they fetched more money then most Campagnolo Victory derailers are worth complete.

-Kurt

yeah. just buy a used one in good shape next time one comes up on dBay. then you'll have one for spare parts!

Propinquity is a wonderful thing, ain't it? Spent the weekend rebuiling my old Raleigh Royale tourer (Worksop 531. early mid 80s - and by the way, we're 7-12 hours ahead of most of you guys ;-]) for a 400km ride I'm doing in France in 3 weeks. It's got late 80s Deore XT drivetrain, and the RD was ticking when it was on the middle crank ring. Reading through this thread, I now have three leads: check the chainlinks, check alignment of the cage (my first thought), and check the chainlength.
Good on you guys - BF foreva!
Jeff