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Chain jumping
Not sure if anyone else has this problem but when I go quickly down a rough downhill section of trail, I go to pedal at the bottom and the chain has jumped from the middle ring down to the granny and occasionally jumps off the front rings all together. This seems to happen about 50% of the time and is now getting quite irritating. Is there something I can do to stop the happening? The chain and cassette are slightly worn now but they have done this from new, I upgraded to a better chain than originally on the bike, to no avail.
I have a Deore Crank set, X7 front derailleur and Sram 991 chain. I also have Sram X9 rear derailleur if that makes any difference.
Thanks in advance for your help.
Edit:- It's a 26" HT 3x9
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put the chain on the largest chainring.
Check that the crank-shaft isn't moving sideways. There's a little spacer that you can screw in or out and if it isn't set right the crank-shaft can move sideways.
Maybe have a look over all the teeth on the rings, if any are damaged they might need replacing.
Happened to me not long ago and thats how we fixed it
chain too long? derailieur spring tension?
shift to the big chainring before you head downhill
There might also be some riding technique changes that can help here to.
the first one, is to lift the back wheel over rough ground ie concentrate on being as sommoth as possible
Second, foot position. I see quite a few riders who when they swap from right foot low to left foot low on the cranks to either corner or to miss rocks, they back pedal to get there this increases the chances of the chain falling off at that point - if at every opportunity you pedal forward, then each time you wind the chain back onto the ring - as its from the bottom that it starts to come off.
If you want to fix it with bling - then go 10 speed, get an xtr shadow plus derailleur - or wait a few months, because i think the new x9 is coming out with s similar system to keep more tension on the chain.
Thanks for the replies.
My technique could be the answer, I'll try to be smoother.
How can I check if derailleur tension is correct? The chain length is the same as when I bought the bike, when I put the new chain on I made sure the number of links was the same. Is there somewhere I can find the correct amount of links I should have? My bike does seem to have the most amount of chain noise of any bike I've heard, I've put a chain stay protector on that helped a bit, but it is still noisy. It's as if the chain is rattling on the front der.
The chain rings are all new, I had a complete bottom bracket/crank set put on about a month ago.
Putting it on to the big ring is ok but what if there's an uphill straight after the downhill?
Have you read the Shimano instructions?
I have found that generally you can remove at least one link from chain as most bikes are setup so you can use every possible gear combination.
See http://www.epicidiot.com/sports/chain_length_cal... or http://www.machinehead-software.co.uk/bike/chain...
Cheers
Evan
+1 to chain length. I went through about 3 front DRs on my first store-bought mountain bike trying to solve the problem with my chain jumping off and missing granny ring on a downshift. It used to jump off even without shifting on the trails occasionally too.
Finally, when replacing the chain, instead of just cutting it the same as the old one as I had been doing, I RTFM and cut it per the instructions, which was to cover big ring and big cog without going through the RD, leaving about half a link pair overlap to spare.
It ended up being 2 or 3 link-pairs shorter. Every new bike I've bought has been the same - chain too long. Why do they do that?
Anyway, the problem disappeared once the chain was set to the correct length and the RD could apply proper tension. Now it's the first thing I check on any bike that joins our quiver.
I still upshift to the big ring on fast rough descents. Stops the chain bashing up the chainstay.
This is done with new bikes because if the chain was the perfect or ideal length it would rip of the RD and the hanger off the bike should the rider decide it a good idea to shift into the big ring and the largest rear sprocket. Most folk know that is a bad thing to do. Certainly those who've shortened their chains. Many, however, don't know this.
The last thing a shop worker wants to experience is some clown blaming the shop for such a mishap....
shortening a chain definately helps, but i wouldnt shorten past the point of taking out the hanger because big big wont fit.
I run a short chain, but i have shifted to big big (well, failed to shift more accurately) - its the sort of thing that happens at night for me - i think i'm in middle ring but i'm in big - not such an easy thing to check when belting along a trail in the dark.
Thanks all for the replies.
I had a look at the web links and ended up watching maintenance videos for about an hour!
I'll have a look at chain length and let you know how I go.
Thanks again
Sometimes I roll the cranks backwards to change feet, maybe to lean on a turn. I think if you do this over a rough section the chain must bounce & drag sideways & then as you turn the cranks it leads all the way around and drops off. Could be to the inside or totally off. Just have to change the habit.
I find if I just pedal forwards it usually goes back on, though it can be noisy if it's dropped to the inside. Reading the comments I might have to take another link out of my chain - but it's shorter than it was when new.
If that happens, it's not the perfect or ideal length - at least, not per manufacturer instructions.
Is it not the whole idea of making sure it is capable of going around big + big plus a tiny bit to spare is to make sure it is as short as possible but no shorter - that is, *without* snapping the chain or causing other damage?
Nevertheless, some do intentionally run it shorter to reduce chain slap and chain jump on rough trails. From what I've been told by a LBS mechanic who runs his AM/DH bike with a double up front and a too-short chain, the chain will part before the RD is damaged, which makes sense to me.
hawkeye, I can get my chain onto big big, but the deraileur is very straight and the chain is tight bottom - the only way you can get it to change is already be in big and change up at the cassette - it simply wont roll over at the big ring on the front, it just crunches away, as if the cable isnt tight enough. Pretty much every bike i've ever bought has been 2 links too long for a start - the giant reign that I am running short when it was delivered in small small the chain rubbed on itself at the deraileur, quite badly in fact.
Brand new bikes are never dialled - i've always had to play with front deraileurs particularly, chain length, and often cable length and routing to get them to work right. This is the case with dual suspension, because what works in the stand at the shop has buggar all bearing on what works when i sit my fat arse on the bike at 25% sag!
pete B has a 3*9 HT set up. That being the case should he be using large large and possibly small small? The advice given here seems spot on re checking chain length and not back pedaling on rough ground. If he was using 2*10 then depending on sprocket sizes, ring sizes and RD length, large large and small small should be able to be used, but on a 3*9?.
Did the bike come with an X9 rear and an X7 front D? If the RD was an upgrade or the bike was put together from parts and not stock - check rear D length is correct (probably a long cage is standard) and the RD is not damaged re tension and alignment. If alignment is out then back pedaling is even worse
As it has done this from new, and assuming it is a 'stock' bike and not a 'bitsa' put together from parts or had 'upgrades', and hasn't been involved in a major stack early in its life, chain length first, then RD issues, then chain ring damage (they are not bent), then chain line, then wheel/frame alignment.
As has been noted go down hill in the largest gear you able to, if followed by a steep uphill then use the front rings to lower gearing quickly for the uphill (from memory think that going from larger chain ring to next lower one is equivalent to dropping three {maybe four} cogs on the rear)
If I'm in the little cogs on the cassette I still prefer to shift up a couple of cogs at the back before dropping a ring at the front, otherwise the chain can still miss the granny ring due to lack of tension.
Go single speed
Thanks for all the advice guys.
I took two links out the chain after setting the length using your advice. Chain slap has all but gone and I didn't have one case of the chain jumping off the ring.
Thanks again
I like it when a plan comes together