[brandonbmx1]

Hey, I have an 05 rockhopper with deore LX cranks(new model). I am having an issue with the chain. Whenever I am in the middle chainring and I apply a little bit of torque, the chain jumps off the chainring and down to the frame by the bottom bracket, completely jumping the 1st chainring. This usually sends me falling forward to smash my knee on my stem, or worse consequences when I am hitting a jump. I would love it for my bike to not shif when trying to accelerate.

Does anyone know what could cause this. The derailleur limits are set correctly. Could it be frame flex? Or Flex within the cranks? Has anyone else had this problem? Any solutions? Thanks.

Brandon

 

[brandonbmx1]

Oh, in case it matters, I have the LX cranks, 9 speed LX cassette, shimano derailleurs and sram 990 chain. All of which relatively new.

 

[binary visions]

My first thought is to check your chainline. Is it relatively straight or is it really out of whack?

 

[-dustin]

just curious, has this been happening since you got the new components, specifically the new front derailleur?

 

[Wumpus]

Maybe it is your middle ring --> http://www.bikemojo.com/speak/showthread.php?t=50711&highlight=shimano




btw -- he replaced the rear cogs and chain before finally replacing the ring which fixed it. Try a Blackspire, Raceface or Salsa one.


Along with Inbred's question, did you just replace something -- chain, cogs, crank?

 

[brandonbmx1]

the crankset is a little older than the rear cassete/chain/derailleur. The cassette and derailleur are the same age, and the chain is about 15 miles newer.

 

[chinkerjuarez]

Sounds like a chainline issue like binary visions said. With the new LX Cranks sets if you don't use the spacers correctly with the bb cups then the chainline will be thrown off. First check to see if you have a 68mm or 73mm bottom bracket. 73 will only use 1 spacer 68 will use 2. A couple of millimeters can make a difference on chainlines. Also check the chain for tight links that can also contribute to the problem.

 

[V-Dub GTI]

take it in to the shop and ask for them to fix it (take all of it off put all back on)

the problem with that is that gets really pricy after a while. Like BV said it is probally the chain line, if you are confident with wrenching on your bike then there are probally some instructions in your manual that came with the cranks, if you don't feel like doing a bunch of work then just take it to the shop and tell them something is wrong with your chainline and it is skipping.