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-   -   Chain drop pedaling backwards. (http://www.bikeforums.net/bicycle-mechanics/936082-chain-drop-pedaling-backwards.html)

dwellman 02-28-14 09:12 AM

Chain drop pedaling backwards.
 
Have an otherwise great shifting, reasonably quiet SRAM Apex set up with one annoying foible: If I spin the pedals backwards the chain drops on to the BB shell. Can adjust adjust adjust the FD all day all night. . . External bearing BB, so I don't think it's that. Bent chain ring(s) maybe? Is there a tool or method to evaluate warped chain rings?

Or is there something else it could be?

Thanks, guys (and/or gals)

Bandrada 02-28-14 10:07 AM

Quote:

Originally Posted by dwellman (Post 16534988)
Have an otherwise great shifting, reasonably quiet SRAM Apex set up with one annoying foible: If I spin the pedals backwards the chain drops on to the BB shell. Can adjust adjust adjust the FD all day all night. . . External bearing BB, so I don't think it's that. Bent chain ring(s) maybe? Is there a tool or method to evaluate warped chain rings?

Or is there something else it could be?

Thanks, guys (and/or gals)

Check for bends or burs on the chainwheel. The less likely factor is that your q-factor/spacing is way off. In that case relocate spacers from the drive side to non-drive side.

Hope this helps.

FBinNY 02-28-14 10:30 AM

If this is happening when the chain is on an inboard rear sprocket (lower gears), it's fairly normal. If it's happening even when the chain is spooling from the outer half of the cassette, is isn't, and you probably have a bent or damaged tooth on the ring, or a bent hanger. When hangers get bent inward (about the only they ever bend) the lower pulley is far inboard of the upper, so the chain in the lower loop is coming from too much of an inboard angle an climbs over the side.

Easy to check for a bent hanger. Shift to a gear which has the RD cage nearly vertical. Put a straight edge (ie. a broomstick) vertical against the right side of the rear wheel, and see ic the RD cage is parallel, or tilted bottom toward the wheel.

A slightly sticky freewheel or freehub can make this worse because it causes a slack lower loop when back pedaling.

bobotech 02-28-14 10:41 AM

I had a bike that did that and it was the chainline being off. Forward pedaling was fine but whenever I back-pedaled on the rear big/smal front, it would drop the chain onto the BB.

Respaced and its better now.

Edit: my BB is an external bearing BB as well, I had the thick spacer on the non-driveside and the thin spacer on the driveside, I reversed them and the shifting and back pedaling is much smoother now.

cny-bikeman 02-28-14 10:56 AM

No point in adjusting the FD, as the chain engages from the bottom when you backpedal. As FB notes you need to specify what gear combo(s) you are in when it occurs. Also very helpful to know if this is new behavior and if so any maintenance or incident that occurred just previous to the symptom starting. A bent hanger is a possible but less common cause. More often it's a bad chainline or poorly tensioned chain.

dwellman 03-14-14 12:49 PM

Gee it's taken me a long time to follow up. .

It is indeed bent teeth on the big ring. :(

fietsbob 03-14-14 01:22 PM

Don't pedal Backwards :bang: it wont get you ahead .

And, Buy one of these Chain Catchers for Road, Cross, and MTB Bikes - K-EDGE


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