B screw not moving jockey wheel away from cassette

el_Pedr0

Dirt Disciple
I've got an Exage 400LX rear derailleur and the jockey wheel is essentially running directly on top of the largest gear in the rear cassette, so I need to increase the gap.

Screwing in the B-screw seems to have no effect when the chain is on. The end of the screw is making contact with the frame, and so the tab on the derailleur through which the B-screw is threaded, does get pushed round. But the jockey wheel doesn't appear to get further away from the cassette. I have dismantled the knuckle, and cleaned and greased the internals. The action of the knuckle spring seems fine.

I think I might have also cleaned and greased the tension spring a few months ago - but can't really remember.

I recently replaced the chain. Replicating the number of links of the original chain. I've also checked using on online calculator and it comes up with the same number of links as I have on my chain.

I can't figure out what's going on. What am I missing here?

While there are no variable settings in the knuckle spring, I can't remember whether there was in the tension spring. Could a wrong setting on the tension spring inhibit the jockey wheel from moving away from the cassette?
 
Is the mech designed to take the the size tooth of cassette you have? As if its not it can be hard to push them any further away sometimes a longer screw works but ofen it ends up at an aukward angle to the tab on the frame.

check the spring holes on the mech are in the right place too.
 
Is the mech designed to take the the size tooth of cassette you have? As if its not it can be hard to push them any further away sometimes a longer screw works but ofen it ends up at an aukward angle to the tab on the frame.

check the spring holes on the mech are in the right place too.
It's all the original kit that came on the bike when I bought it new so I assume that it is designed to go together. I haven't ridden it for 20 years, but I reckon I would have spotted it back then if it had been ill configured. So I think it used to be fine.

The other thing that cones to mind is that I replaced the cable and housing too. I wonder if I've cut the last stretch of housing too long. Could it be that the stiffness in the housing is pushing in such a way as to counteract the effect of the b screw?
 
I know exactly what you mean.

Is the chain tension rotating the whole derailleur forward so the b- screw is no longer touching the steel plate?
Also, the chain tension can overcome the spring tension
Alternately, is the tab on the plate correctly in contact with the derailleur hanger "stop"?
 
Sometimes there are two holes to choose from to slide the spring ends into which adjusts the tension.
There is only one hole in the knuckle spring - so no option to vary there. In the tension spring, there are two 'available' holes close to one another, and two 'unavailable' holes almost 180 degrees away. By 'available' I mean that the hanger has the four holes, but the disc that the spring fits into only has two. Currently the two holes in the disc are lined up with two of the holes in the hanger. It might be that with some pliers and force, I could rotate the disc to line up with the other two holes. But I can't rotate that disc with my fingers and they are precisely lined up with two of the hanger holes, so I don't think I've accidentally moved the disc and and so I am confident that it has always been in its current orientation. I've tried the tension spring in both of the 'available' holes and there's no difference to the B-screw problem.

It does feel like the knuckle spring is being overpowered by something though.
 
Is the chain tension rotating the whole derailleur forward so the b- screw is no longer touching the steel plate?
The chain tension is pulling the derailleur forwards, but 'forward' in my sense is pulling the b-screw with greater force to the frame (as opposed to away from it).
Alternately, is the tab on the plate correctly in contact with the derailleur hanger "stop"?
I'm not sure which part you mean. I'm going to try and take some close up photos....
 

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