I'm quite stumped on this issue i'm having. I took apart the rear derailleur to grease everything and when I put it back together the B spring is pushing the derailleur to the rear of the bike instead of forward.

The thing is though I can't get it installed the way it should be. It twists the spring in the wrong direction so it expands instead of contracting. Could the spring have been changed with the wrong one at some point? Are old derailleurs just made this way?

Did you put it together correctly?

You have to have the unit in a vise or something to hold it, rotate the unit, then lock it in.


Pay attention to about 13:45 on.

It sounds like the spring was tensioned in the wrong direction during re-assembly.

I'm tensioning it the way shown in all these videos. By twisting the plate counter clockwise. Can anyone confirm the job of the B spring is to push the derailleur towards the rear of the bike or towards the front? I'm thinking it might be an issue with the P spring not being strong enough rather than the b spring.

I strip and rebuild every derailleur that I get my hands on, I find it relaxing.

Anyway...
Did you completely disassemble the derailleur? If so it is possible that you swapped the cage spring and the B pivot spring.
There are a few derailleurs that I've come across that the springs are close enough in size that they could be unintentionally swapped.

If you have another RD take a close look at the way the cage spring and B spring rotate. They rotate in opposite directions.

I did but they aren't interchangeable. I even went back and checked. They both have the same coil direction. I'm stumped.

So I figured it out. Turns out B spring is meant to push the derailleur to the rear of the bike. I'm not sure why it's designed like this and it's counter intuitive to the way you would think it would be. My issue was in the P spring not having enough tension any more. I drilled a new tension hole put it all back together and now I get great chain wrap.

Actually, it isn't counter-intuitive at all. To maintain tension in the chain the derailleur has to pull the chain backwards. By limiting the forward movement of the RD body it puts a minimum on how little pull-back the RD can apply. In practice though it is generally used to position the guide pulley w.r.t. the sprockets.

I have never played with that particular RD but I'm guessing your term P-spring refers to one in the upper knuckle, not the spring on the lower knuckle which torques the cage. Regardless though, it would be unlikely that a spring would become so weak that it couldn't at lest do something without breaking first. Most RD's are such that the springs can be pre-torqued enough, either by using a different anchoring hole or by re-orienting the cage on the shaft. If you have to drill a new hole then most likely something else isn't assembled right.

All my issues were solved by tensioning the P spring as shown in the picture. When it was tensioned more, it pulled the B spring forward getting the chain to wrap around the cassette better.