Tiagra front derailleur adjustment

I picked up a 2006 Trek 1200 a few weeks ago and so far so good. The
only problem I've run into is shifting the chain from the middle
chainring to the largest chainring while the chain is on a middle or
larger rear sprocket. I tired adjusting the derailleur via the high
stop screw but any deviation from the original screw setting causes the
chain to pop off when I'm shifting from the middle chainring to the
smallest. Do I need to adjust both the low and high stop screws
proportionately or is there something very wrong with my derailleur.
The only way I can shift to the largest chainring os to first shift the
chain onto the smallest cong first the shift to the largest chain ring.

Ordinarily I would never be on the largest sprocket and chainring at
the same time. I just happened to be on my trainer and decided to play
around with the gears when I ran into this problem.

Javier wrote:
I tired adjusting the derailleur via the high
stop screw but any deviation from the original screw setting causes the
chain to pop off when I'm shifting from the middle chainring to the
smallest.

I would say you never should have used the High and low limit screws
for this problem and that you should have used your barrel adjustment
on your front shifter to bring the INNER cage of the front derailleur
right up to the chain when the chain is on the middle front and largest
rear as described here
http://www.parktool.com/repair/readhowto.asp?id=75

Since you've changed the high and low screws already you'll need to
redo them and then set your cage. Make sure your front shifter is
exactly on #2 when you adjust your front cage. Normally, after your
high and low screws are set you shouldn't have to adjust them again.
All further adjustments should be from the barrel adjuster on your
shifter.

Hope this helps
John

"Javier" wrote in message
ups.com...
I picked up a 2006 Trek 1200 a few weeks ago and so far so good. The
only problem I've run into is shifting the chain from the middle
chainring to the largest chainring while the chain is on a middle or
larger rear sprocket. I tired adjusting the derailleur via the high
stop screw but any deviation from the original screw setting causes the
chain to pop off when I'm shifting from the middle chainring to the
smallest. Do I need to adjust both the low and high stop screws
proportionately or is there something very wrong with my derailleur.
The only way I can shift to the largest chainring os to first shift the
chain onto the smallest cong first the shift to the largest chain ring.

Ordinarily I would never be on the largest sprocket and chainring at
the same time. I just happened to be on my trainer and decided to play
around with the gears when I ran into this problem.

The low screw sets the limit of how far the derailleur will move inboard
(the direction toward the smallest chainring) or stated another way - it
sets the derailleur position when the cable is completely loose.

The high screw sets the limit of how far the derailluer will move outboard
(the direction toward the larger chainring) or stated another way - it sets
the derailluer position when the cable is as tight as it ever gets.

The cable tension sets the actual derailleur position (but no matter how
loose or tight the cable tension is set, the derailleur won't move outside
the high or low limits)

Shimano's service instructions for Tiagra front derailleur explain exactly
how to adjust the high and low limits screws and the cable tension. This is
available at http://tinyurl.com/9w7we

BobT

Javier wrote:
I picked up a 2006 Trek 1200 a few weeks ago and so far so good. The
only problem I've run into is shifting the chain from the middle
chainring to the largest chainring while the chain is on a middle or
larger rear sprocket. I tired adjusting the derailleur via the high
stop screw but any deviation from the original screw setting causes the
chain to pop off when I'm shifting from the middle chainring to the
smallest. Do I need to adjust both the low and high stop screws
proportionately or is there something very wrong with my derailleur.
The only way I can shift to the largest chainring os to first shift the
chain onto the smallest cong first the shift to the largest chain ring.

Ordinarily I would never be on the largest sprocket and chainring at
the same time. I just happened to be on my trainer and decided to play
around with the gears when I ran into this problem.

You need to set the limit screws such that when in the middle ring,
there is a wee bit of chain rub when in the largest and smallest cog,
on the front der. Then the first position is correct when on the small
ring. make the cable tight, shift to the middle, check the clearance in
the small cog, shift to the big cog, adjust the limit screw.

Javier wrote:

I picked up a 2006 Trek 1200 a few weeks ago and so far so good. The
only problem I've run into is shifting the chain from the middle
chainring to the largest chainring while the chain is on a middle or
larger rear sprocket. I tired adjusting the derailleur via the high
stop screw but any deviation from the original screw setting causes the
chain to pop off when I'm shifting from the middle chainring to the
smallest.

You're imagining that. The high-gear limit stop has no effect on
downshifting whatever, it just limits how far outward the derailer cage
can go.

If it's too loose, the chain may overshoot while upshifting and fall off
outward.

If it's too tight, you will have trouble getting the chain to shift to
the big ring, and may find the chain rubs on the outer derailer cage
plate once it gets to the big ring.

Do I need to adjust both the low and high stop screws
proportionately

No, they have nothing to do with one another. The high-gear stop screw
only relates to shifting onto the big ring. The low-gear stop screw
only results to shifting onto the little ring.

or is there something very wrong with my derailleur.
The only way I can shift to the largest chainring os to first shift the
chain onto the smallest cong first the shift to the largest chain ring.

You might need to tighten cable with the indexing adjuster (adjusting
barrel, usually located at the down-tube housing stop.)

A usually reliable source wrote:

You need to set the limit screws such that when in the middle ring,
there is a wee bit of chain rub when in the largest and smallest cog,
on the front der.

Nope, the front derailer's limit screws don't do ANYTHING when the chain
is on the middle ring.

For detailed instructions, see: http://sheldonbrown.com/derailer-adjustment

Sheldon "Derailers" Brown
+----------------------------------------------------------+
| And what are all these mysteries to me, |
| Whose life is full of indices and surds? |
| x^2 + 7x + 53 |
| = 11/3 --Lewis Carroll |
+----------------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

Thanks folks, I'm going to give it anohter shot on Thursday.

Javier wrote:

I picked up a 2006 Trek 1200 a few weeks ago and so far so good. The
only problem I've run into is shifting the chain from the middle
chainring to the largest chainring while the chain is on a middle or
larger rear sprocket.

Depending on the construction of your fder::::::

I have found that some fders can drive you absolutely crazy twiddling the
limit screws, adjusting height above rings, and angle to rings, and still
getting clunky changes.
At least on some older fders that I have come across I believe that the
design is poor.
The designer guy just went off to do fishing rod design after lunch and
left problems with the bike stuff.
The "gap" distance between the inner and outer cheeks at the leading edge
of the fder is too wide for the limited amount of cable movement available
from the gear shifter.
Because of the gap between the cheek and the chain, instead of moving the
chain instantly, the mech just moves air for a while with nothing
happening, losing precious chain movement capacity.
If you adjust correctly for upshift then there is too much distance where
nothing happens on the downshift, and vice versa.
If the construction of the fder allows it (no strap joining the left and
right faces right at the front) then I bend the tip of the left and right
faces inwards towards the chain by about 2mm each (YMMV).
Some fders are already made like this.
This reduces the "gap" just at that point (the area which moves the chain
from middle to larger) so that the distance is closer to the amount of
cable movement available from the gear changer, and turns an absolute
mongrel into a really sweet gear change.

On Mon, 10 Oct 2005 16:25:22 -0400, Sheldon Brown
wrote:

Javier wrote:

I picked up a 2006 Trek 1200 a few weeks ago and so far so good. The
only problem I've run into is shifting the chain from the middle
chainring to the largest chainring while the chain is on a middle or
larger rear sprocket. I tired adjusting the derailleur via the high
stop screw but any deviation from the original screw setting causes the
chain to pop off when I'm shifting from the middle chainring to the
smallest.

You're imagining that. The high-gear limit stop has no effect on
downshifting whatever, it just limits how far outward the derailer cage
can go.

Actually it sounds as though the OP was turning the wrong screw. This
might indeed result in the chain popping off whe shifting from middle
to small ring.


jeverett3ATearthlinkDOTnet http://home.earthlink.net/~jeverett3