bcarter6

No, I am not shifting intentionally while pedaling backwards. But, for example, I pull up to a stop sign and pedal a quarter turn backwards to get the pedal on top and ready to go, frequently the chain will shift to the next cog, or maybe two cogs... I put the bike on the stand and played a bit, I found it happens in a similar part of the chain each time, but I don't see anything bent or damaged. I oiled the chain really well to make sure everything was smooth, still happens.

I'll also say, the bike shifts perfectly when pedaling forward, I have no problems there.

I'm not sure this is a problem other than being really annoying, but I'd still like to know what the problem is and fix it.

Any ideas?

roadfix

If it shifts fine otherwise, you may want to check the derailleur hanger alignment.

DiabloScott

One possibility: worn cogs hang on to the chain too far causing derailleur to take up less slack.

bcarter6

Sorry, I should have mention: the whole system is new. About two months ago I bought a new cassette, new chain, new derailleur, shifters, crank, etc...

2manybikes

The derailleur system is not designed to work when pedaling backwards. The only reason you can pedal backwards is that you have a freewheel. And whatever you do, don't make any adjustments according to what happens when you pedal backwards. That does not work. The bike shifts perfectly when going forward then the bike is fine. Stop pedaling backwards.

bcarter6

Fair enough, thank you

DiabloScott

It still shouldn't happen. Half a stroke backwards for pedal positioning while cornering or stopped at an intersection shouldn't derail the chain.

bcarter - do it in slow motion while off the bike and see what actually happens.

2manybikes

There are pleny of things wrong when you pedal backwards. In some gears you can, in some you can't there is no problem if the bike pedals forward fine. But maybe there is something wrong when pedaling forward that he did not notice. He might be cross chaining. That does not mean there is something wrong with the bike. That means don't cross chain and pedal backwards. Don't adjust anything. Based on what the bike does backwards.

noglider 

I disagree with 2manybikes 90%. It's not a big problem that it shifts when backpedaling, but it does indicate something is wrong. There's nothing wrong with backpedaling. Bikes are designed for it.

The derailleur is not aligned. Make sure the jockey wheels and the rear sprockets are in parallel planes. Bend the hanger to straighten the derailleur, or have your local bike shop mechanic do it for you. There's a specialized tool for this, and it costs about $85.

ctwxlvr

I say there may be nothing wrong with the chain shifting when back peddling, and this is why, the chain ring/ cog alignment may be such that it is the chain ring causing the shift, minor cross chaining, with in acceptable range.

2manybikes

The derailleur does not lead the chain onto the cogs when pedaling in reverse, it is on the wrong side of the cogs. Do not adjust it, The spring tension in the derailleur is backwards and will not keep tension on the chain if you pedal backwards fast. Do not adjust the derailleur. (If it really is OK when going forward)
However they may be something wrong, there may be a stiff link, that should be checked. But it will do that when pedaling forward too, but maybe it's hard to notice.

If he's cross chaining or the bike is not fully shifted or there is a sticking cable that could be it too. It could be lots of things. That means it is not quite perfect when pedaling forward. Or maybe the freewheel is sticking, that happens with cheap bikes. Then you pedal it forward in the stand and let go of the pedals. To see if they spin hard. I repeate the deraileur does not guide the chain onto any sprockets in reverse.

The key may be that he says it happens in the same part of the chain each time. Maybe there is a slightly sticky pin. The above post is correct too.

AEO

chain angle has a lot to do with it.
chain on an angle will try and hop gears until it's relatively straight.

the way to do it correctly: shift down if you anticipate having to stop.
limted to clipeless and toe clip users: you can also grab the front brake hard and lift the rear up to shift down while allowing the rear wheel to spin freely in the correct direction.

try this on any bike with derailers: go big big, now pedal backwards. you chain will auto-shift and then jam eventually.

it's a common problem on my folding bike which is a 1x7 and has to make do with tight chain angles in the extremes.

xenologer

It's just your bike telling you to stop Cross Chaining.
Cross chaining doesn't work well going forward, and works even less well going backwards.

bcarter6

Is it cross chaining using the middle chainring and a 27 tooth cog?

DannoXYZ 

When heading towards a light where you know you have to stop, downshift the front into the small ring. Leave the rear in the middle of the cluster so that you have a straight chainline. Then pedaling backwards won't move the chain.

The front-chainring acts like a derailleur on the top-run of the chain if the chain isn't straight, it will pull the chain towards the cogs that result in a straight chainline. So if you're in the big-ring up front, pedaling backwards will cause the chain to move towards the small cogs if you're not near the right side of the cluster. Same with small chainring, if you're not near the middle of the cluster, pedaling backwards will have the chain try to move up the cluster to larger cogs. This isn't as easy to do and it will just rub and make noise, but not shift.

vikay

I have the same problem and I only noticed this after removing my chain to wash it. I got curious so I tried it on my cheap Walmart MTB and it did the same. I went to the store and tried it on about 10 new bikes. They all did the same.

I believe this is the difference: the new nicely lubed bikes at the store - when you shift, then pedal backwards instead of forwards, the chain gets derailed from the jockey wheel and as you continue pedaling backwards, the chain slides against it giving you the feel that it is working. It corrects itself after pedaling forward hard. The "fix" process was actually pushing the jockey wheel and the lower pulley outwards (looks like if you do this too much it is damaging your RD).

For me, pedaling backwards derailed the jockey pulley, but the inside of the jockey wheel (or the chain) is not lubed good enough for it to continue rotating backwards to slide against it. This caused the RD to be pulled forward.

Anybody saying that this should work should try it on their own bikes in stationary position and watch what exactly happens. It makes sense since when you pedal in reverse, the force is coming from the bottom of the chain/crank set. The roles between the jockey pulley and your cassette are reversed. Your cassette cog is trying to shift gears on the jockey pulley.

fietsbob

Derailleur mechs are made to work with the whole thing going forwards .

if the derailleur guide pulley is Dead On under the cog , you may get it to go backwasrds a bit .

For running the chain thru a rag of example, to wipe off excess dirt & oil
but your hand can mess that up too..


IGH will back pedal better ...

Don in Austin

It is normal for a chain to jump from one ring to another pedaling backwards depending on the following:

Excessively cross-chained gearing selected.

Bike with short distance between BB and rear hub.

Seven speed is not as bad as 9 or more speeds.

Don in Austin

2manybikes

It happens sometimes. The chain tensioner can not keep up if you pedal backwards quickly. And of course the derailleur does not guide the chain onto the cogs. Don't make any adjustments based on what the chain does in reverse. Try not to pedal backwards. The only reason it's possible is that the bike needs to be able to coast when traveling. So there needs to be a freewheeling effect.

The only thing that matters is if the chain works correctly when pedaling forward. I've seen 10 speeds (ten rear cogs), that have insane chain angles, they jump right off if you pedal backwards. They have to, the chain is way off.

BCRider

When pedaling backwards the derailleur isn't guiding the chain. So any amount of cross chaining along the top run can hook a shifter tooth or ramp and pull the chain. Entirely normal and nothing to do with derailleur hangers or derailleur adjustment. Simply the chain is crossed such that when you go backwards it can force the shift.