Wtf?!
 

So I've been having trouble with front derailleur lately. I made some adjustments and after hours of swearing and getting ready to throw my bike in the garbage I finally got the stupid thing to work.

Then I decided to go for a test ride up the street. Well, all of sudden while riding the front derailleur no longer worked. It wouldn't change gears and when it did it just threws the chain off. Ok. Fine.

So then I put the bike back on the stand and was going to fiddle with the thing, but before I did I decided to check it out one more time. I turned the cranks by hand and shifted through the gears. I was perfect! I hadn't done a thing. WTF?!

Another test ride...nada. It was all f'ed up again.

WTF?!

What is happening here?

Need some info...

Type of derailleur?
Double or Triple crank set?
Type of Shifter?

Thanks!

The number one reason for differing stand VS road test function is the tension that's in the chain during riding (and not present during stand testing). If I had a dime for every time I mention "soft pedaling during shifting" to my customers...

There are other reasons for differing function and oldschoolwrench's request for more info is the start of discovery for those. Andy.

Andy has it right, but even with proper technique a front derailleur setup that's a bit off can be fine until you hit the road. The other question is what guidance did you use for the derailleur setup? "Fiddling" with it does not tell us whether you used a good source (sheldonbrown.com, parktool.com) to set up the derailleur height and angle, which are necessary before you start working with the limit screws or cable tension. Throwing the chain off is very common with a too-high derailleur position, as the limit usually has to be set further out.

Could it be a cable tension issue? On the stand are the bars straight ?

Thanks!

I think I figured it out. It was a cable tension issue. After turning the barrel adjuster things seem to be getting better.

this seems like a good time to go off topic
and brag that my recently-converted-to-8-speed-IGH mountain bike
has not made an unusual sound or missed a shift
in the months since i got it together

this morning
i mentioned my conversion to a co worker who also rides
and he said
I wouldn't care if I never saw another derailleur again
although he rides a full suspension mtb
and so the conversion is not as straightforward an upgrade

all i am trying to say is
derailleurs are a pain in the arse

Yes, derailleurs are a PAIN in the a**!

As it turns out the problem wasn't so much with the cable tension.

I finally gave up, ready to toss the bike out the window and dust off my fixie, and decided to take it in to one of the ba-zillion bike shops around town. At first the mechanic thought it was a case of an old/worn/bent derailleur. He was getting ready to replace it when he looked closely at the chain. Apparently, the person I bought the bike from (someone on craigslist) had put a 10-speed chain on the bike. The cassette has only 8-speeds. Problem solved.

It is a well-known fact that cars and bicycles that make funny noises, throw chains, etc., won't do it while a mechanic is around, so I was wondering if your bike was detecting the stand and shaping up accordingly...but sounds like you figured it out.

Doubt it will help you any, but a drivetrain issue like that I will throw the bike onto my floor trainer and use that as a workstand for the purpose, it's not quite road conditions but it's much closer than the drivetrain on the workstand is.

Glad it was just too narrow of a chain btw!

The derailleur behaved badly even for the mechanic, while in the stand. :)