Yes pedaling backwards a little can work. And it comes in handy. It sounded to me that he was doing more than one revolution. That should not be done. The derailleur also is a chain tensioner when pedaling forward, when you pedal backwards quickly you can see the chain go slack a little, because not only does it not have a guide now, it has no proper tensioner. If you spin the pedals backwards quickly the chain can go slack and if there is a big chain angle the chain can come off. What I was trying to say is do not make any derailleur adjustments or make any conclusions about shifting when pedaling backwards. It does not apply. If he pedals forward and everything is OK then he should leave it alone. Because he asked the question about backpedaling, I could tell he was not an experienced bike mechanic, so I did not want to start him making adjustments. He points out in another post that it only happens when cross chaining with a severe angle from big cog to middle, or big chain ring, on a triple. Another sign that he should not be making derailleur adjustments. Big cog to big ring? and back pedaling ? C'mon........holy cow!

There may not be anything wrong with the derailleur adjustment even if he has a problem backpedaling.
The derailleur is not designed to handle this, on some bikes it will, on some bikes it won't, it will be inconsistent, If you work on enough bikes you find out. Just because most people can do it does not mean the next bike will do it too. If you are riding and you do this, for example, if you hit a bump at the wrong time when the chain is slack from backpedaling, that can knock it off even if the bike works perfectly in the bike stand. If you can do it every day on YOUR bike it does not mean anything about HIS bike.

Track bikes with a fixed gear do not apply to this conversation at all, they are too different. Also mountain bikes can put up with a lot more drive train banging around than a road bike. They control the chain better. He was talking about a road bike. It's different. Don't confuse the issue. I was trying to keep it simple, by not getting too complicated. Now it's too late.

Now he's getting derailleur hanger advice! If it works pedaling forward that is the only thing that counts, backpedaling does not count. I have no indication that he has any problems with his bike. The derailleur looks twisted with a severe chain angle. PEDAL FORWARD.........then check out the shifting.

About the beer ! :beer: I'm buying !!!

nah..if the bike is still under the LBS warrenty/ free serive thing, it should be free....

It is a used bike, so there is no LBS warranty. Thanks to everyone who offered advice. Luckily I haven't run any to any problems with this when I am on the road. I just happened to notice this when I was checking my bike out in the garage and pushed the pedals backwards with my hands.

So I have basically learned a good lesson. Don't pedal backwards, and if everything works by pedalling forward, then don't worry.

And........go for a ride. :)

it's not really mindless, considering that cables stretch. hence the reason they put that adjustment screw on shifters. granted if it's skipping while you've got the front derailer on granny, and the rear on the 10 tooth then yeah the chain is missaligned because that's not a practical combination. but if it's in granny up front and on the second gear in the rear and it's skipping, then adjusting the screw on the shifter, can (and has on many of my bikes) solve this problem.

oh, and throwing around insults and vulgarity on message boards to people you will never meet in person is BS. seriously, civility can go a long way.

Well, it's like this. The poster did not say anything about shifting problems when pedaling fowward. If it shifts fine going forward, then the screws and tension don't need fiddling with. Your advise would have caused him to possibly hose a perfectly good derailer adjustment, especialyy that part about truning the adjuster all the way out.Then tossing out the lame 'oh yeah,if that doesn't fix it ,it's somethign else'. Typical mindless advice for any drive train problem is 'adjust the screws', when in fact there are all kinds of other possibilities. AFWIW, Tiagra shifters don't have a cable tension adjustment on them and there is NO 10 tooth cog. And yeah, adjusting for shifting problems casued by improper cable tension is a good thing to do if the situation warrants...

actually there are 10 tooth cogs, so yep, done with you.

Assuming you could actually dredge one up from some obscure source,it wouldn't be found on a tiagra equipped triple.

10 tooth? Where can I get one?

A comment on peoples comments about Sydney's BS-comments.

I had a boss like that once, he would yell at me all over the garage and sometimes almost throwing stuff after me if I didn't hear exactly what he wanted or was a bit slow on getting something. But he was quite nice otherwise and certainly knew his trade so no one really got offended about his yelling. Guess it's the same with Sydney. I got my fair share of "that's BS" from Sydney, ok, maybe it was bs what I said and the next day I get good advice from Sydney on some other issue. Fine with me so why bother about it. No need to get upset about Syd saying "that's BS" from time to time. My experience is that he is usually correct when he says that :D

Here's my experience, in case somebody with same problem gets here:
 

Had same problem. It was the chain; it was made of a very weak metal and was too flexible sideways.

Was able to pedal forward. The derailleurs were keeping the chain in place, but when tried to pedal backward the chain slipped from both chain-ring and freewheel. It didn't happen on all speeds. Just for the sprockets that were not aligned with the chain-ring. Out of 7 speeds/sprockets, I was able to pedal backwards on only 3 of them (on speeds 3-4-5).

Tried to get used to it and use the bike as is, but the chain broke in about 100m; at the first stop (I suppose the chain is most stressed when you stop) Changed with another identical chain and it also broke in 100m. Those bad chains costed me less than 1€ each. Changed with a better chain made of strong steel and less flexible sideways that costed 3€ and I no longer have any problem pedaling backward.:thumb: