tri24

Hi all,

I plan on doing some off road touring, and I figured the best way to know how to fix my bike if something went wrong somewhere out in the wilderness was to build it myself. I thought I was at the part where I would be riding around my parking lot dialing in my indexing, but instead my frame is still in the workstand because I can't figure out why the chain is hopping. It is a soma groove mountain bike. I have sram front and rear derailluer and sram trigger shifters. This is the first bike I've really worked on, so any help is greatly appreciated. I don't have any tight links as the chain hops almost constantly, and I went through by hand and tested each link. I have tried 1/4 increment changes to the B tension screw, but no angle relieves the hopping. The hopping is the most exaggerated with the smallest rear cog and any combination in the front, and I can actually see the chain moving on the jockey wheel and then recoiling when it hits the cog, but I can't seem to fix it. Any suggestions? I don't seem to have any chain flap, but could this happen is this chain was a little too long?

Thanks,
tri24

CaptainCool

Is it worn out?
https://sheldonbrown.com/chains.html#wear
https://sheldonbrown.com/derailer-adj....html#skipping

cascade168

More often than not, this is a cable tension problem. Crank your drive train and get the chain to a point where it's trying to hop to the next gear (talking rear derailleur here). While you are doing this, adjust the cable tension with the barrel adjuster for the rear derailleur and the chain should eventually settle on the next gear and become quiet when you've got the tension correct.

Sometimes, with a rear derailleur, it's possible to get the cable tension off by one whole gear. The easiest thing to do is start over:

1. Shift the shift control to the highest gear (i.e. smallest cog).
2. Loosen the cable tension clamp bolt on the r.d. The cable should now be loose.
3. While the cable is still loose, crank any and all barrel adjusters to minimum tension. This is usually CW as you look at them.
4. Pull the cable tight (just using your fingers is ok) and tighten down the cable tension clamp bolt.

I'm going to assume your limit screws are set correctly. Refer to Park Tool repair section for help.

5. Now crank the drivetrain and do a test shift. There's a good chance that it will shift to the next cog on the first shot. If not, put a couple of 1/2 turns on the barrel adjuster. Test again. Repeat until you can shift back and forth between the first two high gears smoothly.
6. Once you get that good then shift right up and down the cassette. You may need another turn or so to finish off the tension adjustment. Cassettes with a really wide range (like with a MegaRange big cog) can be fussy.

I like to do my r.d. adjustments with the chain on the middle chainring, but that's just me.

I'd suggest you also refer to the Park Tool proceedure for additional information. My proceedure is the stripped down method that I use.

Best luck!

cascade168

One other thing to consider is that you may have a bent r.d. cage. If you don't know how to check this out by eye, a quick trip to the shop should get this affirmed, or not.

tri24

Thanks for all the advice. I tried everything I could think of and everything suggested, but it ended being that the lockring on the rear casette wasn't tightened properly which is why the chain would shift beautifully until you got to the first cog. Now, when this northeaster passes I'm ready to ride. Thanks again for all the advice.

tri24