Anybody had the chain come off the jockey wheel?

[lightning]

So today l had a "mechanical" that l've never had before.

Having just ridden a rocky path at speed, l slowed for a steep descent and suddenly the pedals were hard to turn. l thought the motor had failed.

However a quick inspection revealed that the chain had come come off the lower jockey wheel on the (sram) rear mech and was jammed between that and the cage.

I managed to free the chain and put it back on the pulley, and all was well after that.

However l was left wondering how it came off, because if it was to come off again while l was pedalling at speed it could smash the rear mech into the cassette and make a right mess.

The only thing l will say, is the chain and cassette are quite well worn, because the cassette wouldn't take a new chain so l put the old one back on.

Should l change the drivetrain (chain, cassette, front chainring and jockey wheels) ? The drivetrain has done 1600 miles.

l don't trust it now. Maybe the chain jumped the jockey wheel because a stone hit it?

Have you ever had the chain come off the lower jockey wheel?

 

[Gary]

chain can jump off a jocket wheel for all sorts of reasons.
Only you know how worn your drivetrain is. But by the sounds of it your jockey's probably are worn.
the mech cage may well be damaged from the chain jamming so check that too.

Ps. that's a lot of words to type and not bother mentioning what particular drivetrain parts you're actually asking about?

 

[lightning]

Sorry, it's a SRAM 12 speed ebike drivetrain, NX cassette and GX rear mech.
Drivetrain has done 1600 miles, first chain replaced at 750 miles (worn to 0.5) Cassette jumped in the high gears when l tried to fit a second new chain at 1400 miles (worn to 0.5) so l refitted the old chain.

l do have a complete spare drivetrain.

Rear mech seems to have survived the chain jamming.

 

[Gary]

Just fit the complete new drivetrain when the current one slips.

but inspect the mech and jockey for wear/damage

 

[urastus]

There is a lot of movement with chains, esp when "Having just ridden a rocky path at speed". I don't think that's a coincidence that it happened there. However, is your derailer clutch working / switched on?

 

[lightning]

lt's a SRAM mech and the clutch is automatic l think, you can't turn it on and off as with Shimano.
l've never had the chain come off before, unless it was a stone hitting it, l guess l need to change the chain and jockey wheels. l can't take the chance if l don't know what caused it, the GX 12 speed rear mech seems to be currently unavailable to buy here in the U.K.

 

[Aikone]

I had this happen on a first gen GX, then noticed the second gen I replaced it with had a different profile on the side of the jockey wheel but it still kept happening, I switched to an XO1 in the end which was fine. Though I’ve been on Shimano for 2 years now.

 

[lightning]

l've fitted new jockey wheels, a new chain and new cassette
Although l can re use the cassette after l get replacement gears, it's only the smallest three that jump and you can buy those as a kit.

 

[Mikerb]

You will be fine with the new parts. One reason why the chain may have skipped off the jockey could be very worn bearings wheel which would allow sideways movement or another reason may be very worn teeth which leave a bigger gap between the jockey wheel and the cage.

 

[urastus]

lt's a SRAM mech and the clutch is automatic l think

but is it working? Just try pushing down on the chain - is it stopped by the derailer, or does it move freely to the ground?