What is wrong with my multi-speed bicycle?

[handsomeharry]

Whenever I am seated on my Schwinn, 21 speed bicycle, and riding along, there is no problem.
When I am going up hill, and standing up, pedaling, putting a lot of pressure on the pedal, it feels like the chain slips a little bit. I haven't had any incident, but, it feels like the chain is going to slip off. It does it with either pedal. It's rare that I can watch the chain while I am doing this, but, of the few times that I have, I can't really see any anomalies.
Can you help me?

thanks,
hh

[John Mace]

Your rear derailleur needs to be adjusted. It's not off by much, which is why it doesn't skip when it's not under a load. If there is a barrel adjust, this is an easy thing to do. Turn your bike upside down, and spin the pedals backwards, watching the cog on the derailleur as you turn the barrel adjust-- it should line up directly under the cog you're supposed to be in.

[ticker]

Worn chain/cogs? This can also happen if a badly worn chain is replaced but the cogs, which themselves were worn by the bad chain, were not.

Rear derailleur not adjusted correctly so the chain lies a little off-line from the cog, causing slippage when under high load?

[handsomeharry]

Aha!
It's a fairly new bike, so I guess it's the derailleur!
Thanks, guys!

Best wishes,
hh

[Dag Otto]

It might also be a tight link in the chain. Get off the bike and backpedal while looking at the chain going over the jockey pulleys. If you see the chain hop on that , that's probably a tight link.

[outlierrn]

How new? Cable strech is a normal part of the break in period. They often need to be adjusted in the early days, and occasionally throughout the life of the bike.

[FluffyBob]

I would still check for a stretched chain while you are adjusting the derailleur. After enough use the chain elongates such that the roller on each link rides up against the next tooth of the cog, instead of dropping into the valley between the teeth. This will quickly wear out your chain rings and freewheel, and is easy to fix with a new chain.

Ditto on Dag's comment about the tight link, that is common cause of what you describe.

Park Tool has a nice little repair guide with a click-able map of a bike.

[Magiver]

Originally Posted by John Mace

Your rear derailleur needs to be adjusted. It's not off by much, which is why it doesn't skip when it's not under a load. If there is a barrel adjust, this is an easy thing to do. Turn your bike upside down, and spin the pedals backwards, watching the cog on the derailleur as you turn the barrel adjust-- it should line up directly under the cog you're supposed to be in.

The only adjustment on the derailleur is the hi and low stop that prevents it from coming off either the largest or smallest gear. The adjustment would be in the shifter if it's a modern click-shift unit.

To further explain, a click-shifter is designed to lock into each gear. If it is off then each shift will be slightly off the center-line of the gear.

[John Mace]

Originally Posted by Magiver

The only adjustment on the derailleur is the hi and low stop that prevents it from coming off either the largest or smallest gear. The adjustment would be in the shifter if it's a modern click-shift unit.

To further explain, a click-shifter is designed to lock into each gear. If it is off then each shift will be slightly off the center-line of the gear.

Good point, but not always the case with "click-shift" units. Mine has a barrel adjust, but it's about 10 years old. The OP says he as 21 gears (ie, 7 cog sprocket wtih a 3-ring chain ring)-- that sounds like a pretty old bike.

[Magiver]

Originally Posted by John Mace

Good point, but not always the case with "click-shift" units. Mine has a barrel adjust, but it's about 10 years old. The OP says he as 21 gears (ie, 7 cog sprocket wtih a 3-ring chain ring)-- that sounds like a pretty old bike.

Even a barrel shifter has detents (at least mine does). I adjust it by adjusting the cable length which is done at the shifter just as you would adjust brakes. If you look at where the cable comes into the shifter (for the rear derailleur) it should have a threaded piece that can be turned to lengthen/shorten the cable.

[The Surb]

Check this out too. Sheldon Brown's website has a lot of useful bike info.

[Colophon]

My first guess would be a worn chain. How old is the bike?

It's worth replacing the chain on a bike regularly, like every year, even if there's no slipping problems, because as the chain wears it also wears the sprockets and chainrings down to match the slightly longer links. When you put a new chain on worn sprockets, it will slip, and the only cure is to replace them - which is much more expensive than a new chain.


I tend to replace my chain every 6 months or so, but I do a lot of mileage, both commuting in the week and offroad at weekends.

[butler1850]

Check how tight the pedals are to the crank as well. I had a similar issue on just one side of my mountain bike, and a quick hit with the allen wrench took care of it.

I'd bet it's one of the above explanations though.

[blindboyard]

Had the same thing one my three-speed. Loosened the gear cable, now fine. Don't know how that would equate on a non-Sturmey-Archer gear hub, though.

[handsomeharry]

Thanks for all the help!

For previous comments, my bike is only about 2 or 3 years old, but I dont think it even has 500 miles on it.
OK, what's a tight link? I'm pretty dumb. I haven't read a bicycle since the early 70s, and you can bet, it wasn't multispeed.
Um....

I think that's about it! I'll check out what you all said.

Thanks again,
hh

[johnpost]

Originally Posted by handsomeharry

OK, what's a tight link? I'm pretty dumb.

the chain links should pivot on the pin and so stay tight on the sprocket. if doesn't pivot and stays stiff then it could jump a tooth. if the chain plates are pressed too narrow it might cause this. a dry or corroded chain might cause this.

[casdave]

I bet its chain crossover.

Look at which gears you are using, usually if you are on the largest chainring, you can only get the first five or so smallest sprockets - if you go to the next ones, your chain path is crossed too far and it will rub up against the front derailler.

Similar thing happens when you are on your smallest chainring, you can usually only get the largest five or so sprockets, if you try change to smaller sprockets then it will again pull your chain line across too far.

[John Mace]

Originally Posted by casdave

I bet its chain crossover.

Look at which gears you are using, usually if you are on the largest chainring, you can only get the first five or so smallest sprockets - if you go to the next ones, your chain path is crossed too far and it will rub up against the front derailler.

Similar thing happens when you are on your smallest chainring, you can usually only get the largest five or so sprockets, if you try change to smaller sprockets then it will again pull your chain line across too far.

Good advice, but that's unlikely to be the problem in this case, since it isn't actually skipping a gear. In your scenario, the the front chain ring would drop down to the lower gear, or grind against the derailleur.

[scr4]

Whenever a bicycle is shifting poorly, the very first thing you should do is clean and lubricate the chain.

If you don't want to clean it properly*, at least lubricate it liberally, wipe the chain with a rag, and repeat this a couple of times. Also make sure there is no buildup of crud between the rear cogs, and on the derailleur pulleys.

*The most proper way to clean a chain is to remove it from the bike and clean it in a vat of degreaser or solvent. But a chain scrubber the Park CM5 is my favorite is almost as good. In either case, make sure to rinse away all the degreaser before applying the lube.

[scr4]

Originally Posted by Magiver

The only adjustment on the derailleur is the hi and low stop that prevents it from coming off either the largest or smallest gear. The adjustment would be in the shifter if it's a modern click-shift unit.

Shimano derailleurs have barrel adjusters.

Anyway... If adjusting the barrel adjuster does not solve the problem, and if you are using correct gear combinations*, it's possible that the derailleur mount on the frame is bent. You need a special alignment tool to fix this; best to let a bike shop take care of it.

*The small chainring (the front gear) should only be used with the larger (lower) gears in the rear - you can probably use 1 through 4 on the rear. The middle chainring should work with all rear gears. The large chainring should only be used with the smaller (higher) gears on the rear, maybe 4-7.