Can't get the rear derailleur to work...can't figure out why!!!!!!!!!!!!
I have a Shimano Deore XT derailleur, with Shimano Deore LX shifters. Everything was working fine but the shifting got a little messy so I did everything according to the park tool's tutorial on derailleur adjustment. I adjusted the high screw, the low, then the B screw (I don't really get the B screw because there is a large range of settings for it that seem to all work), then adjusted the barrel on the shifter just like they said to do.
Every time I do this, it's easy to get a nice shift inward (to the biggest cog), but then you shift back outwards and the chain never wants to go back down. So I'm left with the option of adjusting the barrel screw, I guess? I make it looser, but then I have problems going back outward the other way when I shift because the barrel screw is looser now.
It's like only one or the other works, and I've done this whole process literally 20 times, trying all sorts of variations of adjustment, but I can't get this to work. I am pretty sure my derailleur isn't bent, it looks ok, and my chain isn't that old. I am ready to give it to the shop because I have no idea why this isn't working but figured I'd ask to see if anyone knows any tricks.
Last edited by Dibble Donkins; 09-01-12 at 10:52 AM.
I just did that exactly after watching and it does the same thing. It will shift fine going in to the biggest sprocket but then you try to go back down and it doesn't do anything/shifts halfway and the chain rides right in the middle of the two. So I loosen the barrel ever so slightly till it hops outward to the next smallest sprocket, but then the third sprocket has trouble too. After I get over those three biggest sprockets it shifts down fine. But then I try to go and shift back to the biggest sprocket and it doesn't shift because I just loosened the barrel to get it to go down!!!!
I'm using correct combinations of large and small chainrings. Something to note is that I eliminated the largest chain ring and now I essentially only have the middle/smallest on there. So I don't know if that's messing up with the adjustment or not.
The derailleur is oiled and seems to move fine. It has a little scrape on the bottom of the derailleur but that's about it and looks ok.
A scrape on the derailleur can often be a sign that the bike was laid down on the drive side or had some other impact which could have bent the derailleur hanger. That can lead to the type of problem you're having where you can't get the shifting dialed in.
Also, if there is excess cable friction from old cables and housing, gunk on the cable guide under the bb shell, or poor cable housing loops (too small a radius increases drag) there could be some problems for the RD to pull down to the lower cog because the cable is not releasing properly.
You should also double check the b-screw. It can affect how well the system shifts too. You want the guide pulley to be close enough for good shifting but not so close it's bumping the big cog. Hope this helps some!
AHHH it works - all it needed was some olive oil in the cable housings. It makes just that little bit of difference to help shift outwards. It shifts fine now. Surprising because the cables looked fine and 100% clean but I guess they needed some oil.
Last edited by Dibble Donkins; 09-01-12 at 10:01 PM.