Chain skipping problem

OK, I have the common chain skipping problem, however, I think I've
covered all the normal bases in trying to fix the problem....

Bike is a Specialized Crosstrail hybrid, low end components, less than
1 year old, with about 2200 miles on it. Triple chainrings with 8-sp
rear. I rode it through a Northeast winter (road salt, etc.), so it
was pretty gummed up by this spring. Rear derailleur didn't shift
very well (no surprize given its treatment...)

A couple weeks ago I started taking the bike apart to clean out the
winter grime. I took off the chain and rear derailleur, cleaned them,
lubricated, reassembled, and then the chain skipping problem started.
Definite skip at the rear derailleur when under load. I commute
through the city to work, so there's lots of stop and start at red
lights etc.

So then I went through all the usual things to fix a chain skipping
problem. Rear hanger was bent resulting in the rear deraileur cage
not in parallel with the gear. Successfully straightened that. Chain
had stretched a bit, but not that much. A little less than 1/16" in a
foot, but I replaced the chain anyway. Chain is same length as the
original that it replaced, and appears to be correctly sized. That
didn't change the problem. No apparent wear on any gears, so I don't
think it's a new chain/old gear mismatch problem. Plus the problem
happened with old chain/old gears and on new chain/old gears.

Rear shift cable was a bit corroded, so I replaced and lubed the cable
and sheaths. Nice smooth shifts, but still have the chain skip
problem.

Rear deraileur is properly adjusted, limit screws are properly
adjusted, the thing shifts like a champ, just like new. But it still
skips under load.

I've tried running in different gears, I tried the large/large
combination and the small/small combination (I know I shouldn't run
that way, but this was just a test). Chain skipping problem happens
to the same degree regardless of what gear combinations I'm in. I
thought maybe my gears were a bit worn and I just couldn;t tell by
looking, but the problem happens even when I'm in gears that are used
infrequently and so should not have much wear on them.

The last thing I looked at is the freeplay in the rear derailleur. If
I grab the cage, it can wiggle it a lot more than I think I should.
Comparing to the other three rear derailleurs on various bikes in the
garage, this one has much more freeplay. I'm talking about the the
parallelogram part being able to twist in directions that it's not
supposed to twist in. It moves just fine in the diagonal direction
that it is supposed to, however, it *also* moves in directions that is
is *not* supposed to. The derailleur is a bottom of the line Shimano
Altus (I'm not even sure if it is entirely made of metal.)

So before I go to the LBS and buy a new derailleur to try that, does
anyone have any other advice to give me?

Thankx,
Ken

On Apr 3, 1:46*pm, wrote:
OK, I have the common chain skipping problem, however, I think I've
covered all the normal bases in trying to fix the problem....

Bike is a Specialized Crosstrail hybrid, low end components, less than
1 year old, with about 2200 miles on it. *Triple chainrings with 8-sp
rear. *I rode it through a Northeast winter (road salt, etc.), so it
was pretty gummed up by this spring. *Rear derailleur didn't shift
very well (no surprize given its treatment...)

A couple weeks ago I started taking the bike apart to clean out the
winter grime. *I took off the chain and rear derailleur, cleaned them,
lubricated, reassembled, and then the chain skipping problem started.
Definite skip at the rear derailleur when under load. *I commute
through the city to work, so there's lots of stop and start at red
lights etc.

So then I went through all the usual things to fix a chain skipping
problem. *Rear hanger was bent resulting in the rear deraileur cage
not in parallel with the gear. *Successfully straightened that. *Chain
had stretched a bit, but not that much. *A little less than 1/16" in a
foot, but I replaced the chain anyway. *Chain is same length as the
original that it replaced, and appears to be correctly sized. That
didn't change the problem. *No apparent wear on any gears, so I don't
think it's a new chain/old gear mismatch problem. *Plus the problem
happened with old chain/old gears and on new chain/old gears.

Rear shift cable was a bit corroded, so I replaced and lubed the cable
and sheaths. *Nice smooth shifts, but still have the chain skip
problem.

Rear deraileur is properly adjusted, limit screws are properly
adjusted, the thing shifts like a champ, just like new. *But it still
skips under load.

I've tried running in different gears, I tried the large/large
combination and the small/small combination (I know I shouldn't run
that way, but this was just a test). *Chain skipping problem happens
to the same degree regardless of what gear combinations I'm in. *I
thought maybe my gears were a bit worn and I just couldn;t tell by
looking, but the problem happens even when I'm in gears that are used
infrequently and so should not have much wear on them.

The last thing I looked at is the freeplay in the rear derailleur. *If
I grab the cage, it can wiggle it a lot more than I think I should.
Comparing to the other three rear derailleurs on various bikes in the
garage, this one has much more freeplay. *I'm talking about the the
parallelogram part being able to twist in directions that it's not
supposed to twist in. *It moves just fine in the diagonal direction
that it is supposed to, however, it *also* moves in directions that is
is *not* supposed to. *The derailleur is a bottom of the line Shimano
Altus (I'm not even sure if it is entirely made of metal.)

So before I go to the LBS and buy a new derailleur to try that, does
anyone have any other advice to give me?

Thankx,
Ken

Is your "B-screw" properly adjusted ? ( that's the tiny screw that is
at the back perdendicular to the derailer hanger- it helps adjust how
far the chain wraps around the rear cogs). The amount of play on the
rear derailer would be a problem, but it's not driving, so I don't
think that it would be twisting causing your skipping. You might have
put a very narrow new model chain on an older drive system; meaning
the chain might not be seating down on the cogs fully, letting it pop
out under load.

Is your "B-screw" properly adjusted ? ( that's the tiny screw that is
at the back perdendicular to the derailer hanger- it helps adjust how
far the chain wraps around the rear cogs). The amount of play on the
rear derailer would be a problem, but it's not driving, so I don't
think that it would be twisting causing your skipping. You might have
put a very narrow new model chain on an older drive system; meaning
the chain might not be seating down on the cogs fully, letting it pop
out under load.


Good point, I'll try playing with the b-screw. I tried adjusting it a
llittle bit, but that's one thing that I have not spent much effort
adjusting in the past since I have the impression that of all the
derailleur adjustments, that's the one that matters the least.

Bike is less than 1 year old. Original chain was Shimano 8-sp, new
chain is Sram 8-sp. I forget exactly what the model numbers are. But
I'm pretty sure that the chain and gears are compatible. Plus it's
what the (very reputable) bike shop sold me after looking at the
bike.

Thanks,
Ken

So then I went through all the usual things to fix a chain skipping
problem.

like what ? string the system ?
the b screw loosens after loosening the main pivot bolt with an allen
wrench.
the old chain had not worn ? what make is it ? I'll try one.
replacing a chain and not replacing rear cogs is problematic and
normally self defeating.
recheck the wire tautness uo to the grip or shifter. try screwing both
adjusters down even and tight to lock in place over and after placing
chain on middle (or whatever) rear cog then pedal. still skip ?

sheldon brown's website at harris cyclery has photos establishing how
look worn gears and chain.

On Apr 3, 4:12*pm, datakoll wrote:
So then I went through all the usual things to fix a chain skipping
problem.

like what ? string the system ?
the b screw loosens after loosening the main pivot bolt with an allen
wrench.
the old chain had not worn ? what make is it ? I'll try one.
replacing a chain and not replacing rear cogs is problematic and
normally self defeating.
recheck the wire tautness uo to the grip or shifter. try screwing both
adjusters down even and tight to lock in place over and after placing
chain on middle (or whatever) rear cog then pedal. still skip ?

sheldon brown's website at harris cyclery has photos establishing how
look worn gears and chain.

I've read Sheldon Brown's site about derailleur adjustments, checking
for wear, and many other topics (Great site, BTW!). I was a bit
worried about changing the chain w/o changing the rear cassette, but I
thought I got the chain before there was too much wear, and I don't
see any wear on the cassette. Also, the chain skipped with both the
old chain and the new chain. Old chain had stretched a little bit,
less than 1/16" inch per foot. It was a Shimano chain that came with
the bike new. Neither of the bike shops I frequent had Shimano
chains, both had only SRAM, and from what I've read, lot's of people
prefer SRAM over Shimano due to the lack of need for the special
pins. So I replaced with a SRAM chain.

Shift cable is taut throughout. I've replaced the cable and jackets,
so it moves very smoothly now and doesn't get bound up in one spot or
another.

There's a good idea, screwing down both limit screws to lock in one
gear. I don't recall hearing that suggestion before, so I'll give it
a try to see if that changes anything. Thanks!

Ken

On Apr 3, 4:12*pm, datakoll wrote:
So then I went through all the usual things to fix a chain skipping
problem.

like what ? string the system ?
the b screw loosens after loosening the main pivot bolt with an allen
wrench.
the old chain had not worn ? what make is it ? I'll try one.
replacing a chain and not replacing rear cogs is problematic and
normally self defeating.
recheck the wire tautness uo to the grip or shifter. try screwing both
adjusters down even and tight to lock in place over and after placing
chain on middle (or whatever) rear cog then pedal. still skip ?

sheldon brown's website at harris cyclery has photos establishing how
look worn gears and chain.

it is not likely the chain was worn much ( as he said ) given the
mileage and less if he's not a powerhorse rider ( again given the
mileage, unlikely) therefore the damage/ wear to the cogs should be
minimal. you don't have to change the cogs if you replace the chain in
good time, I replace the chain about every 6000kms, 2 1/2 months in
the summer, it'd get real expensive if I had to replace the cogs at
the same time huh? I go about 2+ yrs before I replace those

did you replace the chain, counting the links from the old chain and
installing the new chain with the same number of links - chain tension?
wrote in message
...
OK, I have the common chain skipping problem, however, I think I've
covered all the normal bases in trying to fix the problem....

Bike is a Specialized Crosstrail hybrid, low end components, less than
1 year old, with about 2200 miles on it. Triple chainrings with 8-sp
rear. I rode it through a Northeast winter (road salt, etc.), so it
was pretty gummed up by this spring. Rear derailleur didn't shift
very well (no surprize given its treatment...)

A couple weeks ago I started taking the bike apart to clean out the
winter grime. I took off the chain and rear derailleur, cleaned them,
lubricated, reassembled, and then the chain skipping problem started.
Definite skip at the rear derailleur when under load. I commute
through the city to work, so there's lots of stop and start at red
lights etc.

So then I went through all the usual things to fix a chain skipping
problem. Rear hanger was bent resulting in the rear deraileur cage
not in parallel with the gear. Successfully straightened that. Chain
had stretched a bit, but not that much. A little less than 1/16" in a
foot, but I replaced the chain anyway. Chain is same length as the
original that it replaced, and appears to be correctly sized. That
didn't change the problem. No apparent wear on any gears, so I don't
think it's a new chain/old gear mismatch problem. Plus the problem
happened with old chain/old gears and on new chain/old gears.

Rear shift cable was a bit corroded, so I replaced and lubed the cable
and sheaths. Nice smooth shifts, but still have the chain skip
problem.

Rear deraileur is properly adjusted, limit screws are properly
adjusted, the thing shifts like a champ, just like new. But it still
skips under load.

I've tried running in different gears, I tried the large/large
combination and the small/small combination (I know I shouldn't run
that way, but this was just a test). Chain skipping problem happens
to the same degree regardless of what gear combinations I'm in. I
thought maybe my gears were a bit worn and I just couldn;t tell by
looking, but the problem happens even when I'm in gears that are used
infrequently and so should not have much wear on them.

The last thing I looked at is the freeplay in the rear derailleur. If
I grab the cage, it can wiggle it a lot more than I think I should.
Comparing to the other three rear derailleurs on various bikes in the
garage, this one has much more freeplay. I'm talking about the the
parallelogram part being able to twist in directions that it's not
supposed to twist in. It moves just fine in the diagonal direction
that it is supposed to, however, it *also* moves in directions that is
is *not* supposed to. The derailleur is a bottom of the line Shimano
Altus (I'm not even sure if it is entirely made of metal.)

So before I go to the LBS and buy a new derailleur to try that, does
anyone have any other advice to give me?

Thankx,
Ken

On Apr 3, 4:50*pm, " wrote:
did you replace the chain, counting the links from the old chain and
installing the new chain with the same number of links - chain tension

Yep, exact same number of links. I held up the old and new chains
next to each other. It's interesting to see 1/4" difference in
length just due to the wear at the pins. But it's still the same
number of links. So chain tension should not be the problem.

Plus I tried running in the large front/large rear gear combination to
take up lots of chain slack, and I still get the chain skipping
problem to the same degree. It only happens under load, like whenever
I pull out from an intersection to just get going, or if I try to
crank up a mild hill staying in the same gear as I was in on the
flat. Really makes me not want to stand up to crank hard.

Ken

yeah well maybe its the old chain

wrote:
OK, I have the common chain skipping problem, however, I think I've
covered all the normal bases in trying to fix the problem....

Bike is a Specialized Crosstrail hybrid, low end components, less than
1 year old, with about 2200 miles on it. Triple chainrings with 8-sp
rear. I rode it through a Northeast winter (road salt, etc.), so it
was pretty gummed up by this spring. Rear derailleur didn't shift
very well (no surprize given its treatment...)

A couple weeks ago I started taking the bike apart to clean out the
winter grime. I took off the chain and rear derailleur, cleaned them,
lubricated, reassembled, and then the chain skipping problem started.
Definite skip at the rear derailleur when under load. I commute
through the city to work, so there's lots of stop and start at red
lights etc.

So then I went through all the usual things to fix a chain skipping
problem. Rear hanger was bent resulting in the rear deraileur cage
not in parallel with the gear. Successfully straightened that. Chain
had stretched a bit, but not that much. A little less than 1/16" in a
foot, but I replaced the chain anyway. Chain is same length as the
original that it replaced, and appears to be correctly sized. That
didn't change the problem. No apparent wear on any gears, so I don't
think it's a new chain/old gear mismatch problem. Plus the problem
happened with old chain/old gears and on new chain/old gears.

Rear shift cable was a bit corroded, so I replaced and lubed the cable
and sheaths. Nice smooth shifts, but still have the chain skip
problem.

Rear deraileur is properly adjusted, limit screws are properly
adjusted, the thing shifts like a champ, just like new. But it still
skips under load.

I've tried running in different gears, I tried the large/large
combination and the small/small combination (I know I shouldn't run
that way, but this was just a test). Chain skipping problem happens
to the same degree regardless of what gear combinations I'm in. I
thought maybe my gears were a bit worn and I just couldn;t tell by
looking, but the problem happens even when I'm in gears that are used
infrequently and so should not have much wear on them.

The last thing I looked at is the freeplay in the rear derailleur. If
I grab the cage, it can wiggle it a lot more than I think I should.
Comparing to the other three rear derailleurs on various bikes in the
garage, this one has much more freeplay. I'm talking about the the
parallelogram part being able to twist in directions that it's not
supposed to twist in. It moves just fine in the diagonal direction
that it is supposed to, however, it *also* moves in directions that is
is *not* supposed to. The derailleur is a bottom of the line Shimano
Altus (I'm not even sure if it is entirely made of metal.)

So before I go to the LBS and buy a new derailleur to try that, does
anyone have any other advice to give me?

I assume you already backpedalled in a high gear, watching
for chain rivet troubles, yes? Unless it had a snap link,
chain rivets on eight (& up) speed chains are indeed
troublesome.

If chain is OK, then remove the wheel, work the cassette in
your fingers. Do you feel crunchy bits as you rock it from
backpedal to drive? does it occasionally slip or hesitate
before engaging? I suspect a damaged cassette body since you
seem to know what you are doing and the 'unworn' cogs skip.

Look at the chainrings too, some modern rings are quite thin
and wear amazingly fast.

Worn derailleur body pivots are not related to this problem.
Pulleys are probably worn too, but both of those things are
unrelated to skipping, they just give sloppy shifts.
--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971