Bicycle Mechanics - What causes chain to RUB derailleur plates?

OK. I am no expert but I've done plenty of drive train replacements since i started riding. Rewind to yesterday when it was time to replace the cassette/chain. I took the oppurtunity to remove derailleur pulleys and clean and relube them. That was no problem as i've done this many times before.

Where i did run into trouble was after reassembly of everything, the chain wants to rub on the outer rear derailleur "cage" between the two pulleys. I can't seem to make it stop despite many limit screw adjustments and tension adjustments.

It only seems to happen when chain is on the inner cogs. It rubs so hard that it is almost loud. I wonder if there isn't something wrong with the der. and/or alignment. Awhile back i got into some major mud and the derailleur actually got inverted with the lower pulley above the top until i was able to dig enough mud out.

Any ideas?

are the jockey wheels on correctly?
i suspect that they're not.
the bottom one should not have sideways play at all. the upper one should have some sideways play to aid shifting.

I did them one at a time so there was no way to mismatch them. Unless you can flip them the wrong way. I.E reverse the guide pulley from drive side to facing non drive side.

Other than the above, the only thing I can think of is that the bushings on the wheel opposite the one that is rubbing are not seated fully... In effect this means that the cage at that pulley would be wider than expected, and pinch down the other side decreasing the gap.

Here is a video of the problem. http://www.youtube.com/watch?v=uasEp3J_xCE

Youtube really compressed my video but you can somewhat still see.

Of course it is difficult to know exactly, but based on the angle of the hub and cassette in the video it seems to look like the derailleur is not straight. The RD looks to be pretty vertical while the wheel looks slightly askew.

-D

I am not sure if this is the case or not. I know the bike was less than vertical when the video was shot. I had it in a repair stand pressing on the pedal, so that shifted the bike away from vertical.

Looks bent, nice shirt. :)

I concur, something looks out of alignment...

Did you mount the wheel straight?

Did the hanger or RD get bent in the process?

Did you screw the derailleur in flush to the hanger?

Did you remove or change anything on the RD besides the jockey wheels?

Hanger is DEFINITELY bent.

Rectify and re-assess.

[QUOTE=Little Darwin]I concur, something looks out of alignment...

Did you mount the wheel straight?

YES

Did the hanger or RD get bent in the process?

This is possible. However I compared the hanger to my other Trek 4300 and it looks basically the same. Maybe they are both bent? LIke I said earlier, my derailleur did end up pretty contorted during my mud ride. But i can't see why the hanger would have gotten bent unless the mud was able to do it.

Did you screw the derailleur in flush to the hanger?

I did not dismount the derailleur. It has been on there for about 5000 miles since I installed it over a year ago.

Did you remove or change anything on the RD besides the jockey wheels?

No. Just the jockey wheels.


I suppose i need to try and confirm the derailleur hanger is straight and work from there. Without a guage is this possible to do accurately?

I would have the LBS check the hanger alignment. I don't do that myself, and I suspect the LBS would do it pretty affordably...

Of course, I like to keep my relationship with the LBS good, and I have had the mechanic align drop outs for free without even asking... He just went and grabbed the alignment tool and did it while it was on my car's bike rack... I thought I needed the wheel re-dished. :o

Yeah. I think i'll take it in. I just ordered a bike from them the other day, so they oughta be nice to me.

UPDATE:

Took it to LBS and hanger was fairly bent. He straightened it and all is well. The wierd thing is that it was fine with the old chain and not with the new one. Oh well, the important thing is that it is good to go.