Afternoon y’all,

So i’ve decided to replace my worn out drivetrain and at the same time convert from 3×10 to 2×10. (Shimano XT)

I’ve got a whole new drivetrain including a 2×10 specific front mech.

The problem is that the chain keeps dropping from the small ring up front. The limit screws are bang on in the right place, cable tension etc all good too.

I think it has something to do with the little chain guide thingy below the bolt that attaches the mech to the frame. When I was 3×10 it used to be right up against the granny ring which prevented it dropping off. Now I’m 2×10 the gap between the little guide thing is much wider and the chain just slips between it and the chainring…

The little guide thing didn’t come with the new mech. It is the same one used with my 3×10 mech. Should the new mech have come with one?

Any ideas folks? I’ve got a race next weekend so need to get something sorted before then!

We don’t have the little guide on normal type mechs, and manage fine without it, so I doubt that’s the problem. When you set the inner limit screw, have you checked the clearance with the suspension weighted, it can alter enough to require re-adjustment.Also worth checking the mech’s height is correct.

Yep you shouldn’t need a chain guide on a system with a front mech for normal riding. There are always gaps for the chain to drop off the small ring, but it just shouldn’t happen with the limit screws correctly set up, unless under extreme duress (e.g. crash /dropped bike or a big drop). Even then a well setup system, its rare.

Check the limit screws are correct for all the sprockets at the back, cos the change in chainline might identify you need to tweak the limit screws. And yes, it might need to rub the chain slightly at the extremes, to stop the chain dropping.

Well after several hours fannying around I may have sorted it. No idea how though!

I played with the limit screws, height etc but nothing. It seemed to drop off the little ring whilst attempting to change it up to the big ring?! Doesn’t make sense to me that.

But alas! Just as I was about to set fire to it, it seems to have fixed itself. Which is quite worrying as i’ve no idea what the problem was . Shifts fine now, no drops (as of yet but my driveway and street aren’t particularly rough).

Just don’t want it to drop again whilst riding in anger and bugger the frame up.

A ha! Twigged it. The barrel adjuster on the shifter was playing up. Even when fully wound in, the cable housing was staying out (giving full stretch). Meaning that the barrel adjuster made no difference once the cable was attached so the chain was struggling to make it to the big ring which resulted in the chain dropping.