slow rear upshift on big ring, but not on small?

Lister said:

I have a DA 7400 rear derailleur that is slow to upshift, especially
from the 16 to the 15. Cassette 13,14,15,16,17,19,21,23, rings 42-53.

The rear derailleur upshifts fine on the small chainring.

Less tension on the chain.

Quoted message said:

When I shift the derailleur with my hand on the parallelogram, and
shifters in high position, the derailleur still hesitiates, suggesting
it's not cable drag.

But when I push the derailleur forward slightly, the hesitation seems
to go away. Is there some spring adjustment that would allow the
derailleur to swing forward a bit?

Yes, look underneath the main part of the rear der body and you will
see a screw slot. Turning that clockwise will increase spring return
tension.

Quoted message said:

Cables are new and installed professionally by a fastidious local
mechanic. The B adjustment doesn't seem to help.

Thanks for the response. But I can't see the screw you refer to. The
derailleur is late 80's (low mileage though), maybe before such a screw
as added?

You don't mean what Shimano calls the 'b adjustment' do you? At the
back of the upper part of the derailleur?

Lister said:

I have a DA 7400 rear derailleur that is slow to upshift, especially
from the 16 to the 15. Cassette 13,14,15,16,17,19,21,23, rings 42-53.

The rear derailleur upshifts fine on the small chainring.

When I shift the derailleur with my hand on the parallelogram, and
shifters in high position, the derailleur still hesitiates, suggesting
it's not cable drag.

I don't get it. Why does this experiment lead you to believe that cable
drag isn't the problem?

Quoted message said:

But when I push the derailleur forward slightly, the hesitation seems
to go away. Is there some spring adjustment that would allow the
derailleur to swing forward a bit?

Cables are new and installed professionally by a fastidious local
mechanic. The B adjustment doesn't seem to help.

Suggested experiment: With the bike stationary, put it in the 53/16.
Upshift one click to put it in the "hung" condition. While it's hung up,
pull on an exposed section of cable. Is the cable slack?

If the cable is slack, the shifter is doing its job. If you felt a snag
somewhere, and the shift completed when you released the cable, track
down the snag.

I have a hunch that your shifter may be the culprit. It would be odd or
a derailer to develop a "notch" like you describe. An 8-spd Shimano
shifter is probably not a spring chicken, and the symptoms you describe
are similar to the symptoms of my 8-spd STI shifter a few months ago.
Now my shifter doesn't work at all when the cable is tensioned, but it
works fine when it's off the bike (no tension).

Good luck sleuthing.

--
Dave
dvt at psu dot edu

My theory is that with the derailleur shifted to the 13, then
downshifted by hand pushing on the derailleur, the cable is already
fully slack, and not able to slow the upshift. The other thing that
makes me think it's not the shifter is that it doesn't do it on the
small chainring.

I tried your cable tension experiment. The cable is not slack, but
tugging on it doesn't seem to provide enough give to release it.
Besides, it still shifts promptly when I swing the derailleur forward
on it's top pivot a degree or two.

And re: the first answer from Qui se parla , does it make sense to
increase spring tension, even if I could find the screw, if the low
chain tension situation (small chaniring) is what works? Or does such
an adjustment increase the parallelogram spring tension, rather than
the lower spring tension?

That reminds me of old Campagnolo nuovo record derailleurs having two
holes for the lower spring insertion, presumably to increase or
decrease tension. There doesn't seem to be a second hole in the pulley
cage. Is there another way to increase the lower spring tension
(assuming I want this)?

Lister said:

My theory is that with the derailleur shifted to the 13, then
downshifted by hand pushing on the derailleur, the cable is already
fully slack, and not able to slow the upshift.

I don't follow, so I'll try to restate. You shift normally to the
smallest cog. Then, without turning the pedals, you push the derailer
over to the larger cogs. I don't get what this proves, so I think I
misunderstood your description.

Quoted message said:

The other thing that
makes me think it's not the shifter is that it doesn't do it on the
small chainring.

Yes, that goes against my shifter theory. But I think it also goes
against the derailer theory.

Quoted message said:

I tried your cable tension experiment. The cable is not slack, but
tugging on it doesn't seem to provide enough give to release it.

That makes it sound like the shifter is the problem. If you moved the
shifter a click, but the derailler doesn't move and there is no slack in
the cable, I'm almost certain the problem is in the shifter. If your
shifter is failing like mine did, no amount of tugging on the cable will
release it.

Quoted message said:

Besides, it still shifts promptly when I swing the derailleur forward
on it's top pivot a degree or two.

Most of your symptoms sound like an early case of STI-itis to me. I
don't know how reducing the chain tension fits into the equation.

Another experiment: get the derailer in the "hung" condition between the
16 and 15t cogs. Now twiddle the downshift lever (move the brake lever
sideways) gently, but don't move it far enough to complete a downshift.
You might need to try this a few times before you get it right. If you
can get the *upshift* (16-15) to complete while twiddling the
*downshift* lever, you have a shifter problem.

Quoted message said:

And re: the first answer from Qui se parla , does it make sense to
increase spring tension, even if I could find the screw, if the low
chain tension situation (small chaniring) is what works? Or does such
an adjustment increase the parallelogram spring tension, rather than
the lower spring tension?

I think Peter was talking about the B tension screw. I don't know how to
help with this, since you said the B tension screw had no effect on the
problem.

If you want to pursue the derailer theory some more, you can try to
spray some WD40 or the like in the pivot points of the derailer. If you
can get it to free up, you might want to follow the WD40 with a
lubricant spray.

Good hunting.

--
Dave
dvt at psu dot edu

Thanks again. Sorry, the downshift by hand test is while I'm turning
the pedals.

The derailleur is well oiled and moves freely with no chain or cable.
No noticeable slop in the pivots, or springs.

The shifters work well and have clear clicks and the derailleur moves
quickly, at least in the small ring.

Tried your suggestion of the 'twiddling' the shifter. It moves the
derailleur with each move, but the chain doesn't move to the 15t until
4 or 5 pedal revs, sometimes more. I really don't think the cable is
hung up.

The derailleur working when it's rotated forward makes me think that
normally the top pulley is a bit too far from the cogs. Sideways play
in the chain allows the derailleur to move to the new position, but the
pulley is too far away to send the chain over too, at least until I
nudge the derailleur forward, or it clatters for a few seconds.

It's Z chain, a cheap one. Anyone have a problem with these?

Lister said:

Thanks again. Sorry, the downshift by hand test is while I'm turning
the pedals.

The derailleur is well oiled and moves freely with no chain or cable.
No noticeable slop in the pivots, or springs.

The shifters work well and have clear clicks and the derailleur moves
quickly, at least in the small ring.

I'm feeling sheepish for leading you down the wrong path. I suddenly
realized that I overlooked the simple explanation. Adjust the cable
tension. There is a barrel adjuster where the cable housing enters the
rear derailer. Turn that barrel adjuster into the rear derailer a
quarter or a half turn.

--
Dave
dvt at psu dot edu

The problem happens when the cable tension adjustment is correct. If I
loosen the cable tension so that it moves ok from 16 to 15, I start to
get chatter in the other gears, and even the 15 when it finally shifts.
I think it's probably a pulley distance related issue, or spring
tension. Ever taken one of these apart? I guessing that's my next
step.

Lister said:

The problem happens when the cable tension adjustment is correct. If I
loosen the cable tension so that it moves ok from 16 to 15, I start to
get chatter in the other gears, and even the 15 when it finally shifts.
I think it's probably a pulley distance related issue, or spring
tension. Ever taken one of these apart? I guessing that's my next
step.

Nope, I've never disassembled a derailer body. I don't think you can put
it back together without some special tools -- I think they use rivets
and the like at most pivot points. I've never messed with 8 spd Dura
Ace, though.

You have me stumped. About all I can offer is generalizations:

1) I don't think you've completely ruled out the shifter as your
problem, although you've come close.

2) Even a "fastidious local mechanic" can occasionally kink a cable. I
think you should try that mechanic again with this problem.

3) A derailer developing a hitch between two specific cogs is something
I've never heard of before.

4) A new chain and/or cassette will often improve shifting.

--
Dave
dvt at psu dot edu

Hey, well thanks anyway. I'll post it if I find a solution.

This type of inconsistent shifting can be caused by a frayed cable in
the STI housing. You may want to detach the cable at the derailleur and
push the cable out to inspect it. If the cable is damaged, be sure to
inspect closely for any loose bits of wire left in the shifter.

The cables, inner and outer, are new, sti-appropriate, professionally
installed by one of our best local mechanics.

Shifting is actually very consistent, never a delay on the small ring,
always a delay in the big ring, most evident between 16 and 15, but
also 17 to 16, though less so. Seldom 15-14, never 14 to 13. Also, it
is always solved (on the workstand) by gently pushing the derailleur
forward.

Lister said:

Thanks for the response. But I can't see the screw you refer to. The
derailleur is late 80's (low mileage though), maybe before such a screw
as added?

You don't mean what Shimano calls the 'b adjustment' do you? At the
back of the upper part of the derailleur?

No, the screw under the body of the rear der, not the screw at the
back, where it hooks onto the frame.

Lister said:

My theory is that with the derailleur shifted to the 13, then
downshifted by hand pushing on the derailleur, the cable is already
fully slack, and not able to slow the upshift. The other thing that
makes me think it's not the shifter is that it doesn't do it on the
small chainring.

I tried your cable tension experiment. The cable is not slack, but
tugging on it doesn't seem to provide enough give to release it.
Besides, it still shifts promptly when I swing the derailleur forward
on it's top pivot a degree or two.

And re: the first answer from Qui se parla , does it make sense to
increase spring tension, even if I could find the screw, if the low
chain tension situation (small chaniring) is what works? Or does such
an adjustment increase the parallelogram spring tension, rather than
the lower spring tension?

If in the ig ring, with the associated chain tension, it's not unusual
for the rear der to be slow to pull the chain to the next lower cog.
Where in the small ring, with less chain tension via the rear der, it
would be easier.

Quoted message said:

That reminds me of old Campagnolo nuovo record derailleurs having two
holes for the lower spring insertion, presumably to increase or
decrease tension. There doesn't seem to be a second hole in the pulley
cage. Is there another way to increase the lower spring tension
(assuming I want this)?

dvt said:

I think Peter was talking about the B tension screw. I don't know how to
help with this, since you said the B tension screw had no effect on the
problem.

Nope, 7400 series rear der. Under the body of this rear der is a screw
that pushes a little thing up to increase the return spring tension.
Went away on 7700 and all other rear ders from shimano.NOT the b limit
screw.

Quoted message said:

If you want to pursue the derailer theory some more, you can try to
spray some WD40 or the like in the pivot points of the derailer. If you
can get it to free up, you might want to follow the WD40 with a
lubricant spray.

Good hunting.

--
Dave
dvt at psu dot edu

Lister said:

Hey, well thanks anyway. I'll post it if I find a solution.

'Got a solution.

The same mechanic that installed the cables, when he heard about the
derailleur working when pushed forward, suggested a longer piece of
housing to the derailleur. Worked immediately. The piece he
originally installed didn't look short (or kinked) but the extra length
seems to push the derailleur forward the same way my hand did.

I have subsequently noticed that pro bikes often seem to have generous
amounts of cable casing, and my son's mtb slow upshifting was addressed
by the same fix.

Lister said:

'Got a solution.

The same mechanic that installed the cables, when he heard about the
derailleur working when pushed forward, suggested a longer piece of
housing to the derailleur. Worked immediately. The piece he
originally installed didn't look short (or kinked) but the extra length
seems to push the derailleur forward the same way my hand did.

I have subsequently noticed that pro bikes often seem to have generous
amounts of cable casing, and my son's mtb slow upshifting was addressed
by the same fix.

Good news. I wouldn't have thought of that over the 'net, that's for sure.

--
Dave
dvt at psu dot edu

Yeah, I always feel I've got something for nothing when a problem like
this with old gear is resolved. Of course, that's not counting the
time searching! ;-) Thanks anyway for trying.