chain falls off

[CsharpDev]

When I ride off road I use the small gear in front about 90% of the time and just shift the rear. On 2 occations while riding the chain has fallen off the small gear onto the bb, I put the chain back on and after a few peddles it falls off again... and again... and again.... it seems to happen when I'm on one of the 2 largest gears in the back. The front shifter isn't touching the chain at all on either side so the front shifter at least isn't out of wack, and the rear shifts great.

The temp fix seems to be to shift the rear down to a smaller gear and then back up, assuming it stays on long enough to shift the rear.... and it will work fine after that (no more falling off) Seems to be intermitent as it didn't fall off at all saturday while riding in Lynn.

Any Ideas?

[skippy]

I am still a relative newbie... but I hope my comments here will help....

I had a similar problem, but mine involved my middle chainring (my most common). On one ride in particular my chain fell off 3 times... I kept thinking that I didn't have enough chain tension (could be your problem, but I will let someone go into that), but it turns out that I had a bent tooth. It would seem that when I backpedaled when I was on/near that bent tooth, my chain would move off of the chainring slightly and then when I started to pedal again it would jump off. My solution was to tap the tooth back into alignment with a hammer ::).

Hope that helps!

[Dave]

I too have had this type of problem, it was because my front chainring was worn out. I had a new chain, new rear cassette, but old chainrings up front, so things didn't match up well, and the chain would fly off in the front and suck up into the chainstay, so if your drivetrain is old, this could be part of the issue, but it's usually more evident when you mix old parts with new ones, especially a new chain with old rings like I did. So you might need a new granny gear. check the shape of the teeth on it, if they're angled at the top of the tooth, then they're likely worn out.

[truckboy]

I had this problem and it turned out to be a too-short BB or too-fat rear tire, take your pick. The knobs were grabbing the chain and pulling it off the chainring when it bounced, which it does more of on the granny. Check your derailleur limits too. I find it best to stay in middle chainring and save the small for that last little something on steep inclines.

[CsharpDev]

Entire bike is new and stock, I would hope the BB and tire arn't incompatible sizes. I did notice last night that I am missing a tooth on one of my gears in the rear cassett, but it's the 3rd one from the top, not the gear I'm in when I have the problem. I'm kinda puzzled how I broke a tooth completely off, I could understand breaking a tooth off the large gear in the front from bottoming out... but a middle gear in the rear...?

[C.P.]

Entire bike is new and stock, I would hope the BB and tire arn't incompatible sizes. I did notice last night that I am missing a tooth on one of my gears in the rear cassett, but it's the 3rd one from the top, not the gear I'm in when I have the problem. I'm kinda puzzled how I broke a tooth completely off, I could understand breaking a tooth off the large gear in the front from bottoming out... but a middle gear in the rear...?


This one's a little puzzling, so I must say you need to start with the simple stuff first. Are the bolts that fasten the smallest chainring on the crank tightened up snug? How bout the chain, clean and lubed up? No tight links? No bent links? Sometimes a shift when executed under full pedal load, especially in the smallest chainring, and any of the larger cogs in back, can casue all kinds of havoc to your drivetrain components. It's not unusual to see a bent chain link, missing tooth on a cassette or even a bent chainring (rare). something tells me the missing tooth on your cassette probably led to this problem, and it is now in the form of a bent a link in somewhere on the chain...sound like a possibility? Watch out for those full power granny gear shifts...and take a moment to carefully check all of the links on the chain.

And, if it hasn't been suggested before, a good shifting habit to form is to try to anticipate when you'll need to shift (especially in a climb) and execute it while letting up on the power delivery to the pedals...your drivetrain will thank you.

[CsharpDev]

I'll have to inspect my chain and gears closely tonight. I do tend to shift hard, I guess that explains the missing tooth. Under high stress peddling the rear is still responsive and shifts when told to (although it does complain about it), the front doesn't shift well under hard peddling (which is why I tend to leave it on the small gear in front when off road). I do attempt to lighten up on the peddls a bit when shifting when I can...seems to shift more smoothly that way...

I wonder what the warrenty is on the cassett... maybe the chain was just dirty, I did clean and lube it before riding in Lynn.

[skippy]

Ned Overend's book "Mountain Bike Like A Champion" has a lot of really good info on shifting technique if you have questions (this is where I learned a lot of my skills). Another great book is "Mountain Bike Maintenance" by Mel Atwood -- nice photos and lots of good info.

[slapheadmofo]

Another random hint - forget about that granny ring except for extended climbs and move up to the middle for everything else. The drivetrain will work better and you'll find yourself riding faster and with more confidence in no time. Takes a little more of a 'push' once in awhile, but overall it's much easier and helps so much with obstacles. Give it a shot.

[CsharpDev]

Well bike is in the shop.. the tech noticed some bent teeth on my granny and also there is play in my bb. He's hoping the bb just worked its way loose as it didn't appear broken. Going to clean and rebuild the bb and use lock tight. Also straighten my bent teeth, if he can find the right size gear in his parts bin to replace the one on the rear with the missing tooth he'll replace just the gear, if not I have to buy a new cassett. Once that's all done he'll look for bent chain links. Rough shifting isn't covered under warrenty... he also recomended not using the granny unless I have to and only shifting 1 gear at a time on the rear... he also suggested going rapid rise to force myself to only shift one gear.

[Quo Fan]

I use "low normal" derailers, and I love them. I especially like them because I can down shift while climbing without losing power to allow the derailer to shift. Also, when accelerating, I can up-shift 3 gears at one time.

[CsharpDev]

The Verdict: it needed and got...
straighten bent teeth on chain ring
repace gear with broken tooth on cassett
rebuild loose bottom bracket
tighten rear hub and rotor
straighten bent derailer tab

the tech also cleaned and lubed my chain, cleaned my rotors, adjusted my brakes and shifters, trued my wheels...
I think that was about it... and 3 days ahead of their estimate :)

Grand Total $20... wow I couldn't believe it... The bike is still pretty new and between me and my friends we did buy 3 bikes from them in April so they have been nice to us...

[Ben-O]

The Verdict: it needed and got...
straighten bent teeth on chain ring
repace gear with broken tooth on cassett
rebuild loose bottom bracket
tighten rear hub and rotor
straighten bent derailer tab

the tech also cleaned and lubed my chain, cleaned my rotors, adjusted my brakes and shifters, trued my wheels...


Huh...that's all that was broken? I suppose THAT COULD EXPAIN IT!!! ;D ;D ;D

...good deal on the repair though!