johnadarin

Does anyone know why the chain keeps on falling off on my Giant Seek 1, when I switch gears too quickly or when there is an extreme distance between the front and rear gears? I need to find a solution because it's making me crazy.

I went to my local bike shop and he said that there's nothing to adjust, and to just keep the front and rear gears lined up, somewhere in the middle at all times. What would be the purpose of having 27 speeds if I can't use them all? Thanks, John



2011 Giant Seek 1
1977 Peugeot PX10LE

mulveyr 

Define "When there is an extreme distance between the front and rear gears" please. Are you referring to being in a small chainring in the front while on the largest cog in the back, and vice-versa?

A chain that's too long, or a wheel sliding in the dropout is one possible cause. Is the rear wheel seated as far back as possible? Barring that, possibilities are:

Is it falling off to the inside or the outside of the cranks? If it's the inside, you can install a chainkeeper. Because of the large tooth jumps to the small ring on a triple, it can be difficult to have both good shifting and yet keep the chain from jumping off the small ring. A chainkeeper/dogtooth/etc will help take care of that.

If it's falling off the large chainring to the outside, then you need to adjust the high limit screw on the front derailler.

In either case, your LBS guy is either lazy or incompetent, possibly both.

Also, on a triple, you really don't get 27 gears. You should avoid the small/small and large/large gear combinations. It's also likely that you have a fair number of gear ratios that are so close as to be effectively the same. That's just the nature of a triple/

johnadarin

Yes, it happens mostly when it's on the largest chainring in the front and the smallest chainring in the back. It always falls off the small chainring in the back. It jumps off the smallest rear chainring and gets stuck to the left of it. I usually have to loosen the back wheel, lift it out of the well and put it back on.

Thanks Mulveyr, for your advice. I'll also look into getting a chainkeeper or dogtooth.

Retro Grouch 

How old is the bike? Did it ever work satisfactorily?

Dropping the chain repeatedly is not normal performance. Whenever I encounter a shifting issue that doesn't respond to normal tuneing the first thing that I do is to check the derailleur hanger alignment.

Shift your bike into a gear combination that makes the derailleur arm point straight down. Then stand your bike up vertically against something and examine your rear derailleur from the back of the bike. If your derailleur arm seems to be pointing toward the rear wheel, that's it. Get your local bike shop to realign the derailleur hanger and readjust the derailleur and you'll be good to go.

If it's throwing the chain on the back a chain keeper or dogtooth isn't going to help.

mulveyr 

Big chainring/small cog is a combination that should work just fine.

If I'm understanding you correctly - the chain is coming off and getting stuck between the smallest cog and the second-to-smallest cog? ( "It jumps off the smallest rear chainring and gets stuck to the left of it" ) That should be almost impossible, especially on a new cassette. There shouldn't be enough space for that to happen. When you say "left" - is that "left" when sitting on the bike normally, or looking from the front to the back? If you reversed the meaning and the chain is coming off the small cog and getting stuck between the cassette and the frame, then that's an extremely easy fix by correcting the high-limit screw on the rear derailler. And if that's correct, you really, really, really need to find another LBS. It's literally a 30-second adjustment.

johnadarin

When sitting on the bike normally, the chain jumps off the smallest ring to the rear left (but by my right foot) and gets stuck against the frame. It looks like there isn't enough space and the LBS guy said the same thing, but it actually gets jammed against the frame and the smallest ring. The chain sought of forces its way into that spot which makes it difficult to get it out. It sounds like the high-limit screw adjustment might be the answer. Thanks again.

mulveyr 

Gotcha. OK, the chain is jumping to the right off the cog, not the left, since all directions on a bike are relative to you standing at the rear of the bike and facing forward.

If you're not already aware of it, https://www.parktool.com/blog/repair-...nts-derailleur has great instructions on how to set the limit screws.

johnadarin

Great instructions on setting the screws. Thanks again.

ChowChow

https://www.youtube.com/watch?v=IDJU2KTrXbg&NR=1

johnadarin

thanks, chowchow....great video

contango 

Another vote for setting the limit screws. Any LBS worthy of the name should be able to fix that in no time at all.

johnadarin

Thanks, contango.