Front Derailleur Problems

Quoted message said:

First time that I've installed a front derailleur - it's an XTR top
pull with a 46-38-28 triple. I alinged it with the big chainring
using a 2mm clearance. I'm pretty sure I've adjusted the roatation
properly. The problem is that when I am in the big chainring and
eliminate chain rub, I get massive rub on the inner plate with the
middle chainring. I'm well within the stated capacity (22). It's a
slightly bigger ring than the recommended (44), but I'm assuming that
is not the problem. I suppose I can fix the problem by increasing the
derailleur/chainrign clearance so the middle chainring falls under the
inner plate, but I would guess that would affect performance.

Kind of confused - I've adjusted for chain rub hundreds of times, but
never had problems with chainring rub. Am I missing something? Do I
need to bend the plates? Is there some sort of cage diameter capacity
that I've never heard of? I'd appreacite any input.

Raising or modifying (cutting) the derailer is the only thing you can
do, other than use a smaller middle and possibly inner ring, or larger
big ring. FD's have a "min difference between top and middle ring"
spec. It's 12t for most Shimano mtb derailers.

Quoted message said:

Quoted message said:

Kind of confused - I've adjusted for chain rub hundreds of times, but
never had problems with chainring rub. Am I missing something? Do I
need to bend the plates? Is there some sort of cage diameter capacity
that I've never heard of? I'd appreacite any input.

I would raise the clamp before bending or modifying the mechanism,
just to see if you *can* shift.
I finally got my 48-36-26 working, but had to compromise a bit...I
accepted a slow upshift for a reliable downshift.
This isn't the same issue that you're having, but my point is that a
bit of trial and error can go a long way.
Unfortunately, a derailleur modification error can be tough to recover
from.

How much is your middle ring overlapping the inner plate?
Why the non-standard ring combination? Did you replace just your big
ring?

Quoted message said:

Raising or modifying (cutting) the derailer is the only thing you can
do, other than use a smaller middle and possibly inner ring, or larger
big ring. FD's have a "min difference between top and middle ring"
spec. It's 12t for most Shimano mtb derailers.

Thanks for pointing that out...I had always assumed the 12t was a
*maximum*, not a minimum. Although my bike originally had a 10T
difference (42-32-22)...perhaps I had a 'special' front derailleur.

Is the cage for a double or a triple chain ring? Did you adjust the inner
plate stop?

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news:[email hidden]...

Quoted message said:

First time that I've installed a front derailleur - it's an XTR top
pull with a 46-38-28 triple. I alinged it with the big chainring
using a 2mm clearance. I'm pretty sure I've adjusted the roatation
properly. The problem is that when I am in the big chainring and
eliminate chain rub, I get massive rub on the inner plate with the
middle chainring. I'm well within the stated capacity (22). It's a
slightly bigger ring than the recommended (44), but I'm assuming that
is not the problem. I suppose I can fix the problem by increasing the
derailleur/chainrign clearance so the middle chainring falls under the
inner plate, but I would guess that would affect performance.

Kind of confused - I've adjusted for chain rub hundreds of times, but
never had problems with chainring rub. Am I missing something? Do I
need to bend the plates? Is there some sort of cage diameter capacity
that I've never heard of? I'd appreacite any input.

KnowWhen2HoldemKnowWhen2Foldem said:

Is the cage for a double or a triple chain ring? Did you adjust the inner
plate stop?

<[email hidden]> wrote in message

news:[email hidden]...

Quoted message said:

First time that I've installed a front derailleur - it's an XTR top
pull with a 46-38-28 triple. I alinged it with the big chainring
using a 2mm clearance. I'm pretty sure I've adjusted the roatation
properly. The problem is that when I am in the big chainring and
eliminate chain rub, I get massive rub on the inner plate with the
middle chainring. I'm well within the stated capacity (22). It's a
slightly bigger ring than the recommended (44), but I'm assuming that
is not the problem. I suppose I can fix the problem by increasing the
derailleur/chainrign clearance so the middle chainring falls under the
inner plate, but I would guess that would affect performance.

Quoted message said:

Kind of confused - I've adjusted for chain rub hundreds of times, but
never had problems with chainring rub. Am I missing something? Do I
need to bend the plates? Is there some sort of cage diameter capacity
that I've never heard of? I'd appreacite any input.

Hmmm...didn't think about it being a double cage - I just assumed that
all MTB FDs were for triples. What exactly is an "inner plate stop"?
Do you mean the limit screws? Never heard that term...

David Bonnell said:

Quoted message said:

Quoted message said:

Kind of confused - I've adjusted for chain rub hundreds of times, but
never had problems with chainring rub. Am I missing something? Do I
need to bend the plates? Is there some sort of cage diameter capacity
that I've never heard of? I'd appreacite any input.

I would raise the clamp before bending or modifying the mechanism,
just to see if you *can* shift.
I finally got my 48-36-26 working, but had to compromise a bit...I
accepted a slow upshift for a reliable downshift.
This isn't the same issue that you're having, but my point is that a
bit of trial and error can go a long way.
Unfortunately, a derailleur modification error can be tough to recover
from.

How much is your middle ring overlapping the inner plate?
Why the non-standard ring combination? Did you replace just your big
ring?

Quoted message said:

Raising or modifying (cutting) the derailer is the only thing you can
do, other than use a smaller middle and possibly inner ring, or larger
big ring. FD's have a "min difference between top and middle ring"
spec. It's 12t for most Shimano mtb derailers.

Thanks for pointing that out...I had always assumed the 12t was a
*maximum*, not a minimum. Although my bike originally had a 10T
difference (42-32-22)...perhaps I had a 'special' front derailleur.

I've been playing around with the height adjustment - I've stopped the
rub, but now it won't reliably shift into a lower ring. The overlap
on the ring is quite significant - about 4-5 mm. Somehow I think even
throwing a 50 on the big chainring (to make it a 12T front-middle
difference) won't even do it.

The non-standard spacing is just ignorance on my part. I had a
48-38-28 on and replaced the 48 with a 46 - I didn't forsee this
problem - just paying attention to max chainring size and capacity.
The previous gearing presented no problems to an LX FD. Interstingly
enough, the specific model doesn't seem to exist on the Shimano
website, although it is for sale everywhere (FD M960).

Might have to go with the "custom" fit - picked it up for little $$
anyways....