Jockey wheel cage contacting the freewheel cogs.
 

Here's an issue I haven't encountered before. 1981 Motobecane "Mirage Sport" 12 speed.

When the chain is on the smaller chainring, the cage that protects the jockey wheels actually contacts the cogs in the freewheel.

I'm pretty sure the chain is the right length. I tried shortening it and it was clearly too short.

Original rear derailleur. Original drivetrain except new chain.

Any ideas? See photo.
https://cimg8.ibsrv.net/gimg/bikefor...43000bae14.jpg
Red arrow points to where the aluminum cage that protects the jockey wheels is contacting the outer surface of the 6th cog.

Curious. If nothing changed, what changed?

This is squarely in the b-screw wheelhouse, but a b-screw is not a thing you have...How's the spring tension? Did it lose a turn? Is that a thing that can be lost?

On cantileversthat have a plastic spring retainer, the plastic spring retainer has a tendency to crack & fatigue with age releasing the spring. Could something similar have happened here?

Please educate me as to what a B-screw is. I think the spring tension on the freewheel jockey wheels is right up there.I don't think the spring tension on the derailleur has ever been messed with.

See jpg.

https://cimg1.ibsrv.net/gimg/bikefor...bac53ab216.jpg

I believe the chain is actually too short and is pulling the cage too close to the big cog. Did you duplicate the original chain's length when you installed the new one? Is it a new freewheel with a larger big cog?

I'll try adding a a couple links.

I sized the chain according to the standard method the guys on the Park You-tube videos describe.

I can't remember what happened to the original chain, frankly. This rebuild was long in coming and survived a move. Chain probably got trashed along the way.

Everything on the bike was OEM except for the new chain.

I'll let you know how it comes out.

The b-pivot is the place where the derailleur attaches to the dropout. One some derailleurs, there is a screw next to this pivot, which you can use to adjust the angle at which the derailleur hangs from the bicycle. In most cases, causing a derailleur to rotate clockwise about the pivot (when viewed from the drive side) will cause the jockey wheel and cage to sit farther from the cogs, thus solving the sort of problem you're having.

However, your Huret derailleur does not appear to have a screw for b-pivot adjustment.

In your first photo, where the derailleur bolts to the dropout, see how there's a sort of tab from the derailleur resting against a stop on the dropout, which controls the angle that the derailleur mounts at? You could remove the derailleur from the bike and see if there's some way to adjust that tab; some Huret derailleurs have multiple "stops" that the tabbed washer can be set into, to control this angle.

I think the cage's inner plate being upside down has something to do with the problem... Remove it and reinstall right side up and get back to us with your findings. Andy

Well spotted!

Thanks for all the great ideas, gents!

I'll take the derailleur off and see what you're describing and let you know. It's possible I reassembled the cage wrong.

There's no adjustment screw to allow changing the angle of the derailleur. This was a lower-end bike.

Andy has it exactly right. The inner plate needs to be flipped end for end.

YOU GUYS WERE RIGHT ON!!!

I assembled the cage wrong!

See photos. Any ideas?


https://cimg3.ibsrv.net/gimg/bikefor...0ad53360a6.jpg
(Incorrect)


https://cimg5.ibsrv.net/gimg/bikefor...1b31e208ba.jpg
(correct)

Not the stupidest move I've ever made by a long shot, but the good news is:

1. Nobody got hurt.
2. No money was lost.
3. No permanent damage.
4. Learning experience. This is a mistake I won't make again.

But the saga continues:

I decided to remove the 40 year old largely solidified grease from the hanger cage and spring. Every 40 years or so I figure that should get done.

I can't for the life of me figure out how to reassemble it so the derailleur hangs as it's designed. See photos. There's only 1 hole for the spring.

What the heck am I doing wrong??

See photos:

https://cimg1.ibsrv.net/gimg/bikefor...2ab4568bdc.jpg
It's off by about 180' What gives?
https://cimg6.ibsrv.net/gimg/bikefor...1c916eab69.jpg
other side


https://cimg5.ibsrv.net/gimg/bikefor...d4fa48306b.jpg
disassembled
https://cimg6.ibsrv.net/gimg/bikefor...2f98e289c4.jpg
disassembled

Good eye! That was hard to spot in the photos, at least for me.

Can you pull it down? Maybe it will hang correctly once the chain and wheel are on there.

First picture in this thread might help as a reference as how to it’s supposed to hang.
https://www.bikeforums.net/classic-v...otobecane.html