Chain suck - What causes it and how to fix it?
 

Well, it happened. Twice, in fact. Commuting to work today for only the second time. Cold, windy, heavy back pack and POW! Suddenly the crank arms won't move. The first time I was able to get the chain unstuck from between the smallest chainring and the bottom bracket, but the second time it was stuck for good and I didn't have the right tools (or knowledge for that matter) to get it unstuck. I bailed and used the trusty cell phone to call in a ride.

How can I make sure this doesn't happen again? I'd really rather not go through these ribbings here at work because I had a bike problem.

If it helps any, 2002 Trek 1000 with Shimano Sora components.

PH
:D

Check the height of the front mech (1-2mm above the biggest chainring), and the inner travel setting. This controlled by one of the 2 grub screws on the mech. You need to set it so it just shifts onto the small ring reliably, but no further inboard.
If the chain bounces around, the mech should stop it comming off.

PH,
Hopefully, your problem can be solved simply by adjusting the low limit adjustment on your front derailleur. With your chain on the small chainring and larges cog (ie your lowest gear. Look to see how much distance there is between the inside edge of the chain and the inside of the derailleur cage. That distance should be around 1 mm just under 1/16 inch. Some ders say as much as 2 mm. If it looks like more turn the low limit screw, the one closer to the seatpost, until the gap is small enough.

My question to the experts is what is the difference between "chain suck" and just dropping the chain? Is there any difference?
Regards,
Raymond

John,
Sorry to hear the bad news. What a bummer. Where you having problems shifting when we were riding Saturday?
There may be some information about adjusting your front derailleur in the literature I gave you. If not let me know and I'll email you some instructions with pictures.
Ron

Ron (and everybody else),

Nope, never had this problem before today. Went out and rode a little on Sunday, too and didn't notice any problems.

I got the chain back on the chain rings and took it out for a little test ride at lunch. Seems to "slip" going up hills when I push down hard on the pedals. Can't really say where it slips from because I'm busy watching out for traffic.


PH
:D

Were you shifting at the time? Were you pedalling hard? What gear were you in on the cassette? How many miles on the bike?

I assume it was stuck between the smallest chainring and the chain stay (not really the BB). This is obviously bad for the frame. It may be a mechanical problem or a shifting technique problem or a combination of both.

Some possible causes for 'chainsuck':

1)Worn chain/chainrings.
2) Poor chainline. In addition to increasing the speed of
wear of the drivetrain, poor chainline will contribute to
chainsuck.
3) Mud and/or grit.
4) Bent teeth or 'burrs' on the chainring.

Since you bike is relatively new I would focus on #2 and #3. Since (I asssume) the bike is new, I would take it back to the shop and request that they check and/or re-adjust the drivetrain.

I just cleaned the chain less than 100 miles ago so I'm hoping muck isn't the problem. I'd like to assume that nothing it too "worn" yet since the bike is new.

PH
:D

John,
I don't know where my head is today. :rolleyes:
While I was at lunch I remembered that your bike is about a month old. It's probably time for a "tune-up". Sounds like your cables have stretched and that is part of your problem. All cables stretch when new.
Have you noticed that you have to squeeze a little harder to stop?

Adjusting the limit screw on the front deraileur is just part of fixing your problem but that will get you home.

Call Pedal Power and schedule a tune-up for your bike. It should be free. Maybe free for the first year. Maybe you can drop it off after work one day and pick it up the next.

Ron

>>Were you pedalling hard? Yes

Ease up on the pedalling force as you shift any gear. Shifting the chain under tension is not good for your transmission.

BTW, riding with a heavy back pack is not good for the rider. If this is a regular thing, take a look at luggage racks. The extra weight is negligible, but the bike will take the strain instead of your back.

I'm betting that you have grit/gunk in your freewheel/freehub. Clean it and oil it.

I would clean the drivetrain and then take the bike to the shop for a tune up. I clean and lube my drivetrain at least once a week, no matter how many miles I put on the bike.

I had always heard of chain suck being when the chain is lifted up into the gap between the stay and the rings by either dirty, nicked or worn rings: hence the wide array of bolt-on devices that were so popular in the 90's If your chain is just dropping off the inside, adjusting the limit screw and/or getting a high flanged, narrow BB spacer to keep it out of the cranks should help solve your problem. I had my chain fall off and into the gap between my little ring and the bb shell one time on a night ride- major pain in the a$$ to fix in the dark.

G

Sh*t Happens, get yourself one ofthose "chainsuck blocks", ( I can't remember what they're really called) that mount to the frame to keep your chin from "flying around". There could be several reasons why you get chain suck that a GOOD mechanic who can SEE your set-up may not be able to diagnose or fix successfully. It coud be something as simple as poor shifting technique, severe angles on the chain from extreme gear positions, a frame design that invites "suck", a burr on a chainring tooth, or the mythical Gremlin.

Ride Suckless
Pat

More than you ever wanted to know, I suspect: http://www.fagan.co.za/Bikes/Csuck/

Cheers...Gary

Thanks for posting, Gary. That interesting article confirms my strong aversion to today's ubiquitous "microdrive." No 20T granny rings for me! [Now that I understand chain suck (thank you, Gary!), I also realize that my "obsolete," much-maligned, chainstay-mounted U-brake at least provides protection against it.]

By the way, if chain suck specifically refers to the failure of the chainring to disengage from the slack (bottom) chainline, what do we call chain entanglement caused by a freewheel seizing up and creating slack on the drive (top) chainline?

Chainsuck is very often caused by user error--making front downshifts under pedalling load. Also check chainring teeth for burrs if new and wear if old. It ain't PC to remind people of this but the FEWER gears your bike has the better it will work!

NGear Jump Stop
 

I had similar problems with my 105 triple. I eliminated the chain
falling off the smallest chainring with the NGear Jump Stop, $10. Here
is a review of the product.

http://www.mtbreview.com/reviews/Cha...ct_20650.shtml

For further information see:

http://www.gvtc.com/~ngear/whatis.html

I've been using the NGear for more than two years now and have not had a single chain drop. Works great!

i thought chainsuck was when the chain gets stuck on the chainring you are in, and continues to wrap around the ring causing the cranks to stop turning. i thought its caused by worn rings, and/or mismatched components (new chain, old rings)

the chain dropping off and getting stuck between rings is not chainsuck. from what i understood chainsuck has nothing to do with shifting either.

i used to have a gary fisher big sur that had built in adjustable chainsuck plates. it was cool, but i never had the chainsuck problem on that bike.


anyhoo, correct me if i be wrong

heres a little picture i made in paintbrush of what i always thought chainsuck was......in my pic you can see what i meant in my previous post by the chain continuing to wrap around the ring

You are right legal, that is chain suck. His trouble is the chain slipping off his low ring. Caused by too much slack in the der cable or low der limit screw out of adjustment. Both easy fixes - tighten the cable (most likely) or raise the low limit der screw.

Check your chain. After even one occurance I have found the chain damaged beyond repair, and it never worked correctly until replaced