"Slipping" Power Train

On Nov 1, 2:06*pm, (Arthur Shapiro) wrote:
Got a phone call from my frequent riding partner last night. *Turns out she'd
had a fortunately-minor crash on Sunday. *She was standing on it pulling away
from a light, and all of a sudden there was no resistance - the pedal went
around with no force on it and she went flying off the bike. *Just minor
scrapes and cuts, and a twisted ankle.

She said it had happened several times in the last few weeks, and she hadn't
really focused on it because the problem always resolved within one portion of
a crank revolution. *This is the first time that the sporadic problem had
actually affected her. *(Yeah, not a good attitude; I would personally have
panicked the first time!).

She'd recently put an 11-34 cluster and some sort of mountain bike derailleur
on her Dura Ace-equipped Calfee. *She does a huge amount of monster
climbing. *The chain was replaced at the time but not the chainwheels.

I had a similar problem on my Campy stuff a few years ago where a spring
inside the freehub broke - the one that forces the pawls outward - and
suddenly I was freewheeling. *Of course, that was a non-resolving problem; it
didn't cure itself later within the pedal revolution.

The only things I can think of are something similar to that within the Dura
Ace freehub, or the new chain sometimes riding on the older sprockets and
temporarily not being gripped by the chainwheel teeth.

Any theories out there or advice on how to troubleshoot this issue? *Clearly
she can't just let it slide; this could have been a severe accident under
other circumstances.

Art

It could really be a lot of things. I had this exact symptom start
early in the summer not long after replacing my chain. If replacing
the freehub body which is usually a fairly cheap fix doesn't fix the
problem, it could be a ghost shifting or autoshifting issue.

Got a phone call from my frequent riding partner last night. Turns out she'd
had a fortunately-minor crash on Sunday. She was standing on it pulling away
from a light, and all of a sudden there was no resistance - the pedal went
around with no force on it and she went flying off the bike. Just minor
scrapes and cuts, and a twisted ankle.

She said it had happened several times in the last few weeks, and she hadn't
really focused on it because the problem always resolved within one portion of
a crank revolution. This is the first time that the sporadic problem had
actually affected her. (Yeah, not a good attitude; I would personally have
panicked the first time!).

She'd recently put an 11-34 cluster and some sort of mountain bike derailleur
on her Dura Ace-equipped Calfee. She does a huge amount of monster
climbing. The chain was replaced at the time but not the chainwheels.

I had a similar problem on my Campy stuff a few years ago where a spring
inside the freehub broke - the one that forces the pawls outward - and
suddenly I was freewheeling. Of course, that was a non-resolving problem; it
didn't cure itself later within the pedal revolution.

The only things I can think of are something similar to that within the Dura
Ace freehub, or the new chain sometimes riding on the older sprockets and
temporarily not being gripped by the chainwheel teeth.

Any theories out there or advice on how to troubleshoot this issue? Clearly
she can't just let it slide; this could have been a severe accident under
other circumstances.

Art

Arthur Shapiro wrote:

Any theories out there or advice on how to troubleshoot this issue? Clearly
she can't just let it slide; this could have been a severe accident under
other circumstances.

I vote for sticking pawls in the freehub.

One possibility you don't mention is a twisted chain. This can
easily result from normal driving force applied to a chain which
has come off.

John

John Henderson wrote:
:Arthur Shapiro wrote:

: Any theories out there or advice on how to troubleshoot this issue? Clearly
: she can't just let it slide; this could have been a severe accident under
: other circumstances.

:I vote for sticking pawls in the freehub.

:One possibility you don't mention is a twisted chain. This can
:easily result from normal driving force applied to a chain which
:has come off.

I've seen new chains have a link that's stiff enough it doesn't like
to engage the rear cogs (particularly smaller ones, where it has to
bend more. ).

But without seeing the bike, it's hard to say.

--
sig 11

On Nov 1, 7:06*pm, (Arthur Shapiro) wrote:
Got a phone call from my frequent riding partner last night. *Turns out she'd
had a fortunately-minor crash on Sunday. *She was standing on it pulling away
from a light, and all of a sudden there was no resistance - the pedal went
around with no force on it and she went flying off the bike. *Just minor
scrapes and cuts, and a twisted ankle.

She said it had happened several times in the last few weeks, and she hadn't
really focused on it because the problem always resolved within one portion of
a crank revolution. *This is the first time that the sporadic problem had
actually affected her. *(Yeah, not a good attitude; I would personally have
panicked the first time!).

She'd recently put an 11-34 cluster and some sort of mountain bike derailleur
on her Dura Ace-equipped Calfee. *She does a huge amount of monster
climbing. *The chain was replaced at the time but not the chainwheels.

I had a similar problem on my Campy stuff a few years ago where a spring
inside the freehub broke - the one that forces the pawls outward - and
suddenly I was freewheeling. *Of course, that was a non-resolving problem; it
didn't cure itself later within the pedal revolution.

The only things I can think of are something similar to that within the Dura
Ace freehub, or the new chain sometimes riding on the older sprockets and
temporarily not being gripped by the chainwheel teeth.

Any theories out there or advice on how to troubleshoot this issue? *Clearly
she can't just let it slide; this could have been a severe accident under
other circumstances.

Art

With falling temperatures, suspiscion should natuarally fall to grease
gumming the freewheel pawls. Usually the ticks made should be sharp
and regular when rotating the freewheel/freehub fast or slow. If the
freewheel is barely making a noise and that is not specific to the
design, a gummed freewheel is lkely. Oil is the best lubricant in low
temperatures. With a real and simple freewheel, life is simple, run
the lightest oil through the face of the freewheel until the pawls are
heard to loosen up. At least a partial dissasembly is likely for
freehubs, but see if there is an oiling port as part of the design,
which may or may not be included in the original instructions.

Another problem is the chain skating on top of the freewheel teeth,
particularly when the pair are not matched. The derailleur probably
requires adjustment to distance the jockey pulley from the sprockets
and 4 chain links was always the minimum setting, 6 is safer with a
new chain. It will also help to loosen up a new chain by oiling it
and riding in a warm environment. Indexing should be set by sighting
the jockey pulley to all sprockets paying particular attention to the
problem area. Remember that oil will always help a new derailleur
chain to flex and function properly with the derailleur.

In article ,
says...

She'd recently put an 11-34 cluster and some sort of mountain bike derailleur
on her Dura Ace-equipped Calfee. She does a huge amount of monster
climbing. The chain was replaced at the time but not the chainwheels.

If she replaced the chain but not the chainrings, and the rings are worn
to the point of shark-toothing, the chain could potentially slip out of
the chain-ring teeth and give a free-wheel effect. This has happened to
me a couple of times when I replaced chain on worn rings and was always
solved by replacing the rings.

Usually occured when starting off from stationary, which could just be
due to the higher torques at that time or because, when changing down to
a smaller ring when stopping, the chain didn't fully engage with the
worn teeth.

Mike

On Nov 1, 9:40*pm, (Arthur Shapiro) wrote:
In article , thirty-six wrote:

With falling temperatures, suspiscion should natuarally fall to grease
gumming the freewheel pawls

Thanks for the ideas so far, folks. *I guess I should mention that this is
Southern California, and Sunday was a quite-pleasant day after morning chill
wore off. *I'd vaguely assert that the temperature at that time would have
been at least 70 degrees as this was on the return leg of the morning ride.

It's still not something to ignore, but less likely, look to the
changes made first.

More than likely she would not be in a particularly small rear cog starting
out from the light; she's a very smooth rider, not a power-masher. *I'm more
inclined to think any chain mismatches would be on the chainrings.

The chainring teeth could be ramped if the previous chain was used for
a long time, but if the slippage was here, it would also have occured
with the old chain. There was no comment about a falling chain.

I like the idea of checking for a stiff link

To lose drive so that you fall indicates it's more than a single stiff
link.

(she had the same idea) and of
checking the derailleur configuration. *Presumably the cluster -- jockey
pulley distance is adjustable by diddling the angle adjustment screw,

That's what I'm thinking.
although
I don't really know much about mountain bike derailleurs.

It's still a chain deraillment mechanism. Don't worry.

Just remembered another. Check that the derailleur mounting bolt is
tight. I've ridden along quite happily for miles changing up and
down through my middle sprockets and it was not until I required the
big sprocket that I realised I couldn't get it. There was a little
slip from gears which had otherwise worked well that day. The
required shift is the most likely to get hung up when the derailleur
mounting is loose.

In article , thirty-six wrote:

With falling temperatures, suspiscion should natuarally fall to grease
gumming the freewheel pawls

Thanks for the ideas so far, folks. I guess I should mention that this is
Southern California, and Sunday was a quite-pleasant day after morning chill
wore off. I'd vaguely assert that the temperature at that time would have
been at least 70 degrees as this was on the return leg of the morning ride.

More than likely she would not be in a particularly small rear cog starting
out from the light; she's a very smooth rider, not a power-masher. I'm more
inclined to think any chain mismatches would be on the chainrings.

I like the idea of checking for a stiff link (she had the same idea) and of
checking the derailleur configuration. Presumably the cluster -- jockey
pulley distance is adjustable by diddling the angle adjustment screw, although
I don't really know much about mountain bike derailleurs.

Art

Art

On Nov 1, 2:06*pm, (Arthur Shapiro) wrote:
Got a phone call from my frequent riding partner last night. *Turns out she'd
had a fortunately-minor crash on Sunday. *She was standing on it pulling away
from a light, and all of a sudden there was no resistance - the pedal went
around with no force on it and she went flying off the bike. *Just minor
scrapes and cuts, and a twisted ankle.

She said it had happened several times in the last few weeks, and she hadn't
really focused on it because the problem always resolved within one portion of
a crank revolution. *This is the first time that the sporadic problem had
actually affected her. *(Yeah, not a good attitude; I would personally have
panicked the first time!).

She'd recently put an 11-34 cluster and some sort of mountain bike derailleur
on her Dura Ace-equipped Calfee. *She does a huge amount of monster
climbing. *The chain was replaced at the time but not the chainwheels.

I had a similar problem on my Campy stuff a few years ago where a spring
inside the freehub broke - the one that forces the pawls outward - and
suddenly I was freewheeling. *Of course, that was a non-resolving problem; it
didn't cure itself later within the pedal revolution.

The only things I can think of are something similar to that within the Dura
Ace freehub, or the new chain sometimes riding on the older sprockets and
temporarily not being gripped by the chainwheel teeth.

Any theories out there or advice on how to troubleshoot this issue? *Clearly
she can't just let it slide; this could have been a severe accident under
other circumstances.

Art

Lube the freehub with light oil (motor or Phil's is fine) and check
the derailleur hanger alignment. Also make sure the new cassette
lockring is secure. Of course, adjust the barrel as needed.

On Nov 1, 1:03*pm, David Scheidt wrote:
John Henderson wrote:
:Arthur Shapiro wrote:

: Any theories out there or advice on how to troubleshoot this issue? *Clearly
: she can't just let it slide; this could have been a severe accident under
: other circumstances.

:I vote for sticking pawls in the freehub.

:One possibility you don't mention is a twisted chain. *This can
:easily result from normal driving force applied to a chain which
:has come off.

I've seen new chains have a link that's stiff enough it doesn't like
to engage the rear cogs (particularly smaller ones, where it has to
bend more. ). *

But without seeing the bike, it's hard to say. *

Even sticky derailleur cables can cause this -- high torque to BB,
stuck cable slips and gives ghost upshift -- but misses, giving that
chain slip feel. This is a plausible scenario since the problem
resolved (as I understand from the post). She should grease her
cables, among other things.

I was dealing with the same problem on my commuter for the last week.
Greasing the cables (particularly at the BB) solved everything. It's
amazing what a little grease can do in the right places. I didn't
crash, but I had some pretty good wobbles.

-- Jay Beattie.