Chain leaves rear roller

[jlfunder]

I have a SRAM APEX 9 speed system (2 chainrings) 3 years old that has worked well until I took it apart to clean it. I put on a new chain too. Now in high range/low gear (crossing over) the chain jumps off the distal derailleur wheel, causing me to have to get off and reposition it. It is clear that the angle of the chain going from the big wheel on the cluster to the big chainring is causing this. It seems like the guides on the sides of roller wheel should be close enough to prevent the chain from jumping off. Did I put it back together incorrectly? Is the chain too short ? All opinions welcome.

[attachment=4071]

[Painkiller]

pic to narrow. lets a side view of the whole chain around the cogs thru the pullys

[jlfunder]

(04-12-2013, 10:01 AM)painkiller Wrote:  pic to narrow. lets a side view of the whole chain around the cogs thru the pullys

That's a really hard picture to get -very busy background. I will give it a try tonight. Here's the latest thought. There are two wheels (pulleys) on the derailleur cage, big and little. The SRAM documentation never shows them clearly but most pictures of the cage show the idler pulley (the wheel most distal to the hub) as equal or bigger than the guide pulley (close to hub). I currently have the small one in the idler position. Maybe I have them switched?

[RBurrelli]

That is entirely possible. Can't tell from your picture but make sure that the chain is properly running through the derailleur. It wraps around your rear cassette and passes overtop of the top pulley gear and then around the back side of the lower gear.

[FredS]

Not the best pic, but the chain should look like this if it is ran correctly

[torquecyclerepairs]

Did you remove and refit the jockey wheels?