Bicycle Mechanics - Chain slips off jockey wheel when backpedaling.

Hoping someone can help out the new guy.

I have an '85 Eddy Merckx that I've been building up with Super Record. The problem I’m running into is that the chain slips off the guide pulley when spun backwards (even just a quarter turn).

When I sight down from the top it looks like the jockey wheels are not perfectly in line. My first thought was a bent hanger but that checked out to be straight. So I am wondering if there could be something bent or out of alignment with the derailleur itself?

This is my first time using technology from this vintage, and I have been told about the overshift/trim back method when using these old campy RDs. When the bike is on the stand and I am patient, I can find a perfect place on each cog that prevents this from happening. However, since I don’t seem to hear many people complaining about this topic, I'm hoping that it is more than just user error!

-Thanks

Note- The jockey wheels are Suntour sealed bearing. They have some wear, but not to a point where they would be at fault IMO. Maybe the whole problem is the result of the RD rejecting the Japanese parts!

The guide pulleys are meant to guide the chain 'onto' the proper cassette when peddling forward not guide the chain 'off' when back peddling.
You didn't mention if it does it in all gear combinations or not but I'll bet it mostly slips off when the chain angle is the most severe between the guide pulley and the chainring.

I think the words above are wise indeed.
The other question I have is that I assume that you are using a freewheel ... if so how old is it?
As the pawls in the freewheel wear or the internals of a frewwheel dry out, it will not want to coast or back pedal as easily which will either cause the chain to go slack or your derailleur and pulleys to start acting up.

Thanks for the responses gents. This problem does occur across the entire freewheel (7spd). It is about as old as the rest of the components but still buttery smooth and easy to spin.

I keep thinking that the hangup is due to the fact that the jockey wheels are not in the same vertical plane. I mean they are close... but not perfect. Is it common for the pulley cages to get bent? CV guys?

I can try to get some pictures up if that will help.

Not sure if this helps (and I'm no mechanic so I might be completely off base) but fwiw I had the same problem as the OP with a 1985 Suntour derailleur, and the mechanic at my LBS said the problem was because the jockey wheel teeth were so worn. There was apparently enough chain tension when pedalling (forward) that it wasn't a big problem, but low-tension backpedalling yielded instant chain dump off the jockey wheels.

Just don't back pedal .. coast or apply power, to go forward.

derailleur has to be dead under the cog in the back, to back pedal,
if its not it will pull the chain off line.

I Only do a slight back pedal on my 3 speed , to ease its shifting.
it uses no derailleur.

[QUOTE=fietsbob;12522567]Just don't back pedal .. coast or apply power, to go forward.

It is sounding more and more like user error. I guess I can't blame my components after all. DarnIT!

In my defense, when I say backpedaling it would be to reposition my launch foot at a stoplight (I live in the city). Or even any time I need to walk my bike backwards (elevators, apartment etc).

I do no extraneous backpedaling.

Cheers.

Well if you've tried everything else, here is one more. Is the chain ok? If the links are not in good shape, they could cause your problem I'd think. But I maybe just grabbing at straws here.

IMO there's something going on if you can't back pedal without losing the chain...

I'd say one of the most likely possibilities is the angle of the dangle; can't really imagine what else might cause it other than maybe the aforementioned worn teeth.

At getting on for 30, it could just be wear in the derailleur's pivots - have you checked how much side to side play you can get out of the bottom of the cage without actuating the parallelogram? Or it could just be a bent hanger...

If you want to stick with period gear and can't fix or replace the derailleur, you could just tweak it on the bike, so the hanger matched the derailleur, so to speak...

Best to use a good derailleur and get the hanger checked, though.

SOLVED!

Upon closer examination I discovered that the pulley cage was slightly twisted. I was able to straighten it and that seems to have taken care of the problem.

Thanks everyone for the suggestions.