Gears jam under heavy load

sidarkin

Hardware...
Stumpjumper FSR 2005
Original Octalink Chainset
New HG93 chain
Original XTR rear mech

A symptom has just developed whereby the chain/gears will just jam under very heavy load. It's difficult to see whats happening as it's tricky to look down when you're applying the sort of pressure that make this happen but as far as I can tell the chain doesn't want to leave the front chainring and the rear derailleur gets pulled forward until everything jams.

The gears are well adjusted chain is new and well lubed, the derailleur appears to be in good shape, the froont chainrings are clean. Has anyone any ideas what could cause this?

None of this happens under moderate load.

ratty2k

Chainsuck, looks like time for new chainrings. We get this regular up in the Dark Peak with all the grit on the trials. Wears the rings out quicker than normal and they become slightly hooked and dont release the chain properly

stumpyjon

Second that, sounds like classic chain suck. If you get it at low speed try to stop without back pedalling and you'll see the chain hasn't released off one of the chain rings (often the small one in my case as it's the one I use the most).

I'd try to work out which ring is giving you problems and replace it.

sidarkin

Cheers for the info guys, those rings have seen many a gruelling ascent so that's a good shout, will break out the macro zoom tomorrow for some forensic examination.