Shimano 48-36-26 MTB setup

David Bonnell said:

I have a 9-speed Deore crankset, paired with an XT front and XTR rear
derailleur. The front will not reliably shift, even though everything
is in good working order (no stuck pivots, cable routing is good,
cables are not sticking).

The biggest problem is that the chain refuses to drop onto the granny
ring at the *worst* times. Occasionally it will co-operate, but the
outer FD plate simply isn't putting enough lateral force on the chain
to move it. The FD is parallel to the chainrings and is as close to
the rings as possible without actually making contact.

Any ideas on how to improve the shifting (short of going back to a
44-32-22)? Shimano still offers these chainring options on their
crankset, so I would assume that there must be a way to set up proper
shifting...unfortunately, I haven't found the magic formula yet.

Cheers,
Dave

are you using shimano chain?

Quoted message said:

are you using shimano chain?

Good point...and no, I'm not. It's of the SRAM variety (I believe it
is a PC-991), but I was told that they're perfectly compatible.
Perhaps not? I've got no particular grudge against Shimano chains
(barring that 10-speed chain snapping incident), but the SRAM
PowerLink is one handy little device. When I swapped cranksets I also
got a new chain and cassette, so a Shimano chain hasn't touched this
drivetrain (yet).

Would this mean that a SRAM chain on an otherwise Shimano-equipped
bike would cause these problems even if I was using a 44T ring?

On an entirely different bike setup, an FSA Energy Compact 50-34 with
a 12-27 Ultegra rear cassette I was using a Sram PC-991. I could just
get it to shift right but it seemed like 1/4 turn either way on the rear
der. and it wouldn't shift as clean. I switched to a
Connex/Wippermann which seems to be working a bit better. It stays
in tune and is easeir to adjust. So I don't know if it would make a
difference with your setup. I've certainly never had problems with 8sp
Sram chains.

In article
<[email hidden]>,
[email hidden] says...

Quoted message said:

Quoted message said:

are you using shimano chain?

Good point...and no, I'm not. It's of the SRAM variety (I believe it
is a PC-991), but I was told that they're perfectly compatible.
Perhaps not? I've got no particular grudge against Shimano chains
(barring that 10-speed chain snapping incident), but the SRAM
PowerLink is one handy little device. When I swapped cranksets I

also

Quoted message said:

got a new chain and cassette, so a Shimano chain hasn't touched this
drivetrain (yet).

Would this mean that a SRAM chain on an otherwise Shimano-

equipped

Quoted message said:

bike would cause these problems even if I was using a 44T ring?

David Bonnell said:

I have a 9-speed Deore crankset, paired with an XT front and XTR rear
derailleur. The front will not reliably shift, even though everything
is in good working order (no stuck pivots, cable routing is good,
cables are not sticking).

The biggest problem is that the chain refuses to drop onto the granny
ring at the *worst* times. Occasionally it will co-operate, but the
outer FD plate simply isn't putting enough lateral force on the chain
to move it. The FD is parallel to the chainrings and is as close to
the rings as possible without actually making contact.

Any ideas on how to improve the shifting (short of going back to a
44-32-22)? Shimano still offers these chainring options on their
crankset, so I would assume that there must be a way to set up proper
shifting...unfortunately, I haven't found the magic formula yet.

Cheers,
Dave

Which xt fd is it? This problem often comes up if using a chain
narrower than the FD was intended for, ie a 7 or 8 speed era FD with a
9 speed chain.

If that's not the issue, how much gap have you currently got between
the chain and the inner FD plate in the lowest gear combo? Shimano
specs an extremely low amount of space here ("between 0 and .5mm"😉,
and it just doesn't work in practice sometimes - sometimes you need to
increase the gap a bit so that the fd can move inwards far enough. But
you also need to make sure that chain drop remains impossible. You've
tried playing with the low limit screw, right? And adjusted cable
tension to match, if necessary? Also, have you lubed the fd pivot
points?

If nothing else works, you can jack the limit screw out some, and if
that causes chain drop then install a chain catcher. That approach
should only be necessary with parts that aren't all that compatible,
like the aforementioned wide-derailer-cage-with-narrow-chain scenario,
and if you're using indexing shifters then it will probably cause rub
in several middle/large ring and smaller cog combos, which sucks.

Quoted message said:

Which xt fd is it?

The FD is a M750, RD is a M952 (both marked with "mega-range"😉.
Shifters are also M750. No problem there. I do have a M760 FD on
hand that I may try...

Quoted message said:

how much gap have you currently got between the chain and the inner FD plate in the lowest gear combo?

I have a fair bit of space between inner FD plate and chain in the
lowest gear (much more than 1mm). The reason, of course, is so that
the outer plate provides enough 'push' on the chain when
downshifting. The problem then moves to the largest gear...when
running in 48-11, the chain rubs on the outer FD plate (particularly
under load).

Quoted message said:

tried playing with the low limit screw, right? And adjusted cable
tension to match, if necessary? Also, have you lubed the fd pivot points?

Yes, yes, and yes 🙂 The FD is in great condition, and operates as
smoothly as you might expect an XT 'railer.

I just looked at a Shimano compatibility chart, and apparently I
require a different FD. Mystery solved, but it's *so close* to
working properly.

Cheers,
Dave

David Bonnell said:

Quoted message said:

Which xt fd is it?

The FD is a M750, RD is a M952 (both marked with "mega-range"😉.
Shifters are also M750. No problem there. I do have a M760 FD on
hand that I may try...

Quoted message said:

how much gap have you currently got between the chain and the inner FD plate in the lowest gear combo?

I have a fair bit of space between inner FD plate and chain in the
lowest gear (much more than 1mm). The reason, of course, is so that
the outer plate provides enough 'push' on the chain when
downshifting. The problem then moves to the largest gear...when
running in 48-11, the chain rubs on the outer FD plate (particularly
under load).

Quoted message said:

tried playing with the low limit screw, right? And adjusted cable
tension to match, if necessary? Also, have you lubed the fd pivot points?

Yes, yes, and yes 🙂 The FD is in great condition, and operates as
smoothly as you might expect an XT 'railer.

I just looked at a Shimano compatibility chart, and apparently I
require a different FD. Mystery solved, but it's *so close* to
working properly.

According to Sheldon, you should be able to make your current
derailleur work if you grind the lower edge of the outer plate to match
the curvature of the 48-tooth ring. See "derailer/chainwheel mismatch" at:

http://sheldonbrown.com/derailer-adjustment.html#front

Quoted message said:

According to Sheldon, you should be able to make your current
derailleur work if you grind the lower edge of the outer plate to match
the curvature of the 48-tooth ring. See "derailer/chainwheel mismatch" at:

http://sheldonbrown.com/derailer-adjustment.html#front

Neat. The curvature of my FD definitely doesn't match the 48T
chainring. If the M760 doesn't work I'll give the grinder a shot.

Thanks again,
Dave

Nate Knutson said:

Which xt fd is it? This problem often comes up if using a chain
narrower than the FD was intended for, ie a 7 or 8 speed era FD with a
9 speed chain.

For what it's worth, I am using a Deore 7sp FD with a 48-38-24 crank,
with a 9sp. setup. No shift problems. I do use a chain watcher to help
with shifts to the 24T chainring, but this predates the 9sp rear setup.

BC

On Tue, 31 Jul 2007 07:44:38 -0700, David Bonnell <[email hidden]>

Quoted message said:

Quoted message said:

are you using shimano chain?

Good point...and no, I'm not. It's of the SRAM variety (I believe it
is a PC-991), but I was told that they're perfectly compatible.
Perhaps not? I've got no particular grudge against Shimano chains
(barring that 10-speed chain snapping incident), but the SRAM
PowerLink is one handy little device. When I swapped cranksets I also
got a new chain and cassette, so a Shimano chain hasn't touched this
drivetrain (yet).

Would this mean that a SRAM chain on an otherwise Shimano-equipped
bike would cause these problems even if I was using a 44T ring?

Perhaps installing a 1 mm shim on drive side of bb will move the right
arm out and let the derailleur push the chain harder and down.

Quoted message said:

Perhaps installing a 1 mm shim on drive side of bb will move the right
arm out and let the derailleur push the chain harder and down.

I had considered migrating to a 113mm BB spindle instead of my current
110, but never mentioned it because I figured it would be considered a
'silly' solution. According to the docs, this would still meet the
chainline requirement for the crankset.

Any ideas where to find such a shim? I had no idea they existed. I'm
using a square taper BB, if that helps.