Drivetrain has started having this problem in the past few days – sometimes when I stand up and pedal hard the chain will slip from the outside ring (I’m on 2×9, 32t shimano) to the granny. It only seems to happen with one gear at the minute, this one being the second smallest on the cassette. It also makes a kind of skipping noise when in this gear. Why would this happen? It’s quite a new drivetrain (had about 4-5 rides on it) with a brand new KMC X9 chain, since the sram one I had initially was shite and suffered from snappage/pins coming out of the plates, despite the low mileage!

Only thing I’m thinking is that the derailleur isn’t adjusted properly and pushing it off as I’m not very good with adjusting the front mech.. but wouldn’t this happen all the time rather than just under pressure? It also doesn’t seem to be that close.

Help me so I don’t have to go back to 1×9 just to save headaches!

bump?

A couple of things.

– have you built this bike yourself?
– is there any noise when pedalling along easily? Any chain vs mech rubbing?
– are you sure – really sure the chainline in right
– are you sure the cassette / chaingrings are new?

Bent link?

http://www.mtbr.com/cat/drivetrain/chain/kmc/x9/PRD_412481_110crx.aspx

Tom start from the beginning again with the whole set up.
One-new chain and gear skipping problems- I would suspect a stiff link if it was not happening before. Put it in top gear and turn the pedals backwards slowly and watch for the bottom jockey wheel jumping. When it jumps check that section of chain for stiff link (eased by correcting connecting pin position or just wiggle chain plates side to side diagonally till stiff link goes. Check whole chain.
If its not that take off chain and start with the front mech. Put shifter in lowest gear so cable is slack.Disconnect the cable and ensure gear pod cable adjuster is set to all the way off and set inner and outer limit screws. (Outer by pressing mech out using thumb).
Now do the same with rear mech remeber that you want cable at slackest point ie on Normal rise shimano smallest casette ring. Disconnect cable and set limit screws.
Reconnect cables taught but only by pulling gently with fingers or it will be too tight.
Now your drivetrain should be properly indexed, any small and I mean small adjustments shuld then be made at the shifter barrels a quarter of a turn at a time but if you have done it all spot on anyway you should not need to do any adjustment.
remeber when setting limit screws on the rear that the top jockey wheel should be vertically aligned directly under the relevant inner and outer cassette rings. On the front shifter you are looking at 1-2mm clearance on the chain.
If all this fails make sure your front deraillieur has not been moved up/down or kicked skew. the outer plate should be parallel to the outside chainring and be running about 3mm clear of the teeth.
Enjoy the sweet feeling of success once you have cracked it-honest its easy.

What type of bike. My FS did the same when the linkage bearings were done. If a FS can you wiggle the rear from side to side?

It’s a hardtail so that rules bearings out!

Thanks for the in depth reply Suggsey 🙂 I followed the park tools guide to set it all up but I think I’m too hamfisted with delicate stuff like this to get it just right. All the shifting seems to be ok, it’s just this slipping problem. I’ll check the chain for stiff links.

– have you built this bike yourself?
– is there any noise when pedalling along easily? Any chain vs mech rubbing?
– are you sure – really sure the chainline in right
– are you sure the cassette / chaingrings are new?

-yes I built it myself. It’s mostly all old/well worn parts, bit of a mess to be honest!
-it’s hard to tell over the sound of tyres and my squeaky brakes, but I think there’s a bit of noise, again only when in that gear and it doesnt sound like chain on mech noise.
-not sure about chainline, how do you check and adjust this?
-the cassette and chainrings are definitely new, I bought em from merlin in December and have hardly used the bike.

-the cassette and chainrings are definitely new, I bought em from merlin in December and have hardly

Well the good news is you’ve ruled out 90% of the common problems!

I presume a new chain at the same time?

Yeah it was a new sram chain. Unfortunately it kept snapping/pins coming out of the side plates, so I’ve just replaced it with the KMC x9. I don’t think I would have used it enough with the sram to wear it enough to cause problems though.. it had probably 20 miles on it if that.

Funnily though this wasn’t an issue with the sram, I think it did appear when I got the KMC the other day. So it probably is somehow chain related.