slipping chain

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hi everyone,i have a problem i hope someone can help with.i have a giant xtc hardtail and i have just replaced the chainset,chain and casette, the problem i have is when i go up steep hills in the mid chainring 9 times out of 10 the chain jumps off the chainring resulting in a bashed knee :mad: ,the gears change up and down no probs. when there is not much load on the chain or i stay seated it behaves itself:confused: .all that was replaced is shimano deore for deore, i noticed a bit of play in the rearmech so will replace that.the chain is correct length.any help would be much appreciated.

Sounds like bent and/or badly worn teeth on the middle chainring to me. I've had problems in the past with the chain jumping off and missing the little chain ring on the downshift, but to do it without any shifting taking place... :eek:

Bear in mind that even if you've replaced the rear cassette and chain, a worn chainring can still chew out your chain pretty quickly. And a well-worn chain can return the favour when you replace chainrings and cassette. They all need to be matched within a wear range to give best life.

I have a chainwear indicator and it seems I need to swap the chain out for a new one every 3000km. As my offroad distance increases I expect that distance to go reduce and the replacement frequency to increase.

I also favour SRAM chains off-road as you can pull them off without having to push out pins with a chain breaker if you use the power link. This enables me to clean the thing properly in kerosene, something you can never really do as effectively if you leave it on the bike - no matter how good your cleaning machine.

Sounds like bent and/or badly worn teeth on the middle chainring to me. I've had problems in the past with the chain jumping off and missing the little chain ring on the downshift, but to do it without any shifting taking place... :eek:

Bear in mind that even if you've replaced the rear cassette and chain, a worn chainring can still chew out your chain pretty quickly. And a well-worn chain can return the favour when you replace chainrings and cassette. They all need to be matched within a wear range to give best life.

I have a chainwear indicator and it seems I need to swap the chain out for a new one every 3000km. As my offroad distance increases I expect that distance to go reduce and the replacement frequency to increase.

I also favour SRAM chains off-road as you can pull them off without having to push out pins with a chain breaker if you use the power link. This enables me to clean the thing properly in kerosene, something you can never really do as effectively if you leave it on the bike - no matter how good your cleaning machine.


The OP has indicated that he has replaced the chainset so I would be surprised if it were chainrings.

Is the front mech set up correctly?

The OP has indicated that he has replaced the chainset so I would be surprised if it were chainrings.

Is the front mech set up correctly?AH, I missed the comment about the chainset. However, unless he's changed them all at the same time or within a week or so depending on mileage, wear and/or bent teeth are still something I'd look at.

I'm assuming that it's not DR adjustment, since it happens not when changing gear. Within that, I'm also assuming xlcelt has enough nouse to set it up so that the chain and front DR don't rub when on the middle chainring except perhaps when in the smallest or largest rear cog and that he has the standard chainring combination.

That leaves:

Worn/bent transmission components. This includes individual teeth on the ring. They don't have to be bent by much, as I found out.
Frame flex
Flex in crank/crank spindle
Unintentionally bumping the shifter
Faulty shifter
Poor chain line due to poorly selected BB and/or cranks, or a bent/misaligned frame
Bumpy terrain taken at speed (although unlikely here)
I'd also be interested to know what xlcelt weighs. If he is solidly built, it could have a bearing on the problem (pardon the pun).

AH, I missed the comment about the chainset. However, unless he's changed them all at the same time or within a week or so depending on mileage, wear and/or bent teeth are still something I'd look at.

I'm assuming that it's not DR adjustment, since it happens not when changing gear. Within that, I'm also assuming xlcelt has enough nouse to set it up so that the chain and front DR don't rub when on the middle chainring except perhaps when in the smallest or largest rear cog and that he has the standard chainring combination.

That leaves:

Worn/bent transmission components. This includes individual teeth on the ring. They don't have to be bent by much, as I found out.
Frame flex
Flex in crank/crank spindle
Unintentionally bumping the shifter
Faulty shifter
Poor chain line due to poorly selected BB and/or cranks, or a bent/misaligned frame
Bumpy terrain taken at speed (although unlikely here)
I'd also be interested to know what xlcelt weighs. If he is solidly built, it could have a bearing on the problem (pardon the pun).

i think you may be onto something with the chainline, especially if he has just changed the crankset. Tis quite possible that the new crankset has a different chainline even though it is a straight deore/deore switch (if he had gone from a taper to a splined for example). Would be useful to know whether the bottom brack was replaced at the same time. Id probably rule out frame flex. I agree that worn components would be the most likely cause.

hi guy's thanks for the replys.to answer some questions,the bb is a taper and i can't detect any movement in it, i am 6'5", 95kilos,all the components were changed at the same time, i changed everything as it kept missing gears and it was all overdue (3 years old :o )but cannot remember if it jumped the mid chain ring then, (it may have:confused: ).the cranks are slightley different in that the old ones were shimano deore, now i have shimano deore hollowtech, (could it be that?). as i said before the gears change up and down no problemwhen there is not much load , and also up and down the chainset with no rubbing.i think you may be onto something with the chainline, especially if he has just changed the crankset. Tis quite possible that the new crankset has a different chainline even though it is a straight deore/deore switch (if he had gone from a taper to a splined for example). Would be useful to know whether the bottom brack was replaced at the same time. Id probably rule out frame flex. I agree that worn components would be the most likely cause.

As you have said, the rear mech has play.
The answer may lie there or with the rear mech cable.
It doesn't take much for a shimano 9 speed system to play up.
Dirty cables or slightly bent rear derailieurs or dropouts are more often the cause than slightly worn derailieurs.
I would change the rear outer and inner cable and check the derailieur alignment first.

hi guy's thanks for the replys.to answer some questions,the bb is a taper and i can't detect any movement in it, i am 6'5", 95kilos,all the components were changed at the same time, i changed everything as it kept missing gears and it was all overdue (3 years old :o )but cannot remember if it jumped the mid chain ring then, (it may have:confused: ).the cranks are slightley different in that the old ones were shimano deore, now i have shimano deore hollowtech, (could it be that?). as i said before the gears change up and down no problemwhen there is not much load , and also up and down the chainset with no rubbing.I'm around 80kg fully loaded with backpack, and I reckon Deore is the absolute bare minimum spec for someone of my weight.

Even so, I managed to bend the teeth over on the Deore-level middle chainring on my hardtail - and at that stage that was from riding purely on the road without anywhere near the force levels you would employ off-road.

I subsequently upgraded teh middle and big chainrings and front DR, and put on a Third Eye chainwatcher just for insurance, and the reliability has given me confidence enough to begin venturing off-road - which I'm now finding quite addictive! :o

Other than confirming the chainline is still good, it looks like you've done all the right things. Maybe upgrade the middle chainring to something Hone or XT level? The saying "Light. Strong. Cheap. Choose any two" seems to be just as true of transmissions as it is the rest of the bike, unfortunately.

Maybe go to your LBS and demonstrate the problem to the mechanic? He may see somethign we're all missing.

A final thought is that when doing steep uphills it's often better to stay seated and spin it up smoothly anyway - getting out of the saddle tends to produce big torque surges on the downstroke which breaks traction at the rear more easily.

here's an update on the bike,today got a deore lx rear mech,took old one off and fitted the new one,when i adjusted it,the chain line was so out i had to adjust the front as well:eek: took the bike out inbetween the showers and did a couple of medium climbs, and so far so good:D.i think as the rear mech wore i adjusted it so far,(the pivot was worn and so was the springs)the poor chain did'nt have much chance,i think as it all looked fine when i put some pressure on it the rear mech just jumped about changing the chain line.monday i will give it a good blast up some hills, but so far so good.I'm around 80kg fully loaded with backpack, and I reckon Deore is the absolute bare minimum spec for someone of my weight.

Even so, I managed to bend the teeth over on the Deore-level middle chainring on my hardtail - and at that stage that was from riding purely on the road without anywhere near the force levels you would employ off-road.

I subsequently upgraded teh middle and big chainrings and front DR, and put on a Third Eye chainwatcher just for insurance, and the reliability has given me confidence enough to begin venturing off-road - which I'm now finding quite addictive! :o

Other than confirming the chainline is still good, it looks like you've done all the right things. Maybe upgrade the middle chainring to something Hone or XT level? The saying "Light. Strong. Cheap. Choose any two" seems to be just as true of transmissions as it is the rest of the bike, unfortunately.

Maybe go to your LBS and demonstrate the problem to the mechanic? He may see somethign we're all missing.

A final thought is that when doing steep uphills it's often better to stay seated and spin it up smoothly anyway - getting out of the saddle tends to produce big torque surges on the downstroke which breaks traction at the rear more easily.