Confused over M739 Front Derailleur

[Lou Carpenter]

I'm confused over the M739 FD and was hoping someone could help me. Am I right in saying the M739 cranks were available in either 42-32-22 and 44-32-22 options? And so the M739 FD should work for both shouldn't it? Or does it? Perhaps there were two different FD's depending on which crankset you had? I looked at the service instructions for the M739 FD and it only lists the 42-32-22 as an option, not the 44t option. Anyone?

 

[Lou Carpenter]

I should add I've tried my M739 FD with the 44-32-22 option and it doesn't work. The chain either passes just beneath, or catches the corner of the bit of metal sticking out that is shaped to push the chain from the middle ring onto the granny. I don't think it is faulty, it just doesn't look like it is meant to work with this combo. For the record the FD is positioned as low as I can get it.

 

[Cloverleaf]

Yes, 44 outer ring was an option. And there were quite a few versions of the front mech - do you have a pic of which one you've got?

 

[hamster]

They will work with a huge variety of chainring sizes - I've used them with rings all the way up to 48T.
The low-band type seem more tetchy and IME perform worse than high-band types.

Set the mech outer cage when extended about 3mm above the large ring and you should be fine.

 

[Lou Carpenter]

Yes, 44 outer ring was an option. And there were quite a few versions of the front mech - do you have a pic of which one you've got?

I can take a photo for you later if you want but it just looks like every other M739 FD I've seen and I have a few, google it if unsure. The different FD's you mention would have different M numbers wouldn't they? There isn't different versions of the M739 FD is there? Which ones are you thinking of?

They will work with a huge variety of chainring sizes - I've used them with rings all the way up to 48T.
The low-band type seem more tetchy and IME perform worse than high-band types.

Set the mech outer cage when extended about 3mm above the large ring and you should be fine.

It may well work with larger chainrings but I think the key here is the difference between top and middle. For example you may get it work with other combinations that have a 10t difference like a 48-38-28, is this what you have? I'm struggling because it is a 12t difference. I take your point about it being a low band but it should still work shouldn't it? Although as I said earlier the 44-32-22 option was not listed in the service instructions.

The cage is set as low as I can get it, about 1mm above the large chainring and it is still too high for the 12t difference.

 

[Cloverleaf]

I can take a photo for you later if you want but it just looks like every other M739 FD I've seen and I have a few, google it if unsure. The different FD's you mention would have different M numbers wouldn't they? There isn't different versions of the M739 FD is there? Which ones are you thinking of?

Simply trying to help, and a pic would identify the part better - I've got a box with perhaps ten XT mechs in it and there are numerous changes between the various types despite all being from the same version of XT. There were top pull and bottom pull versions and, IIRC, both top swing and bottom swing. The latter may have been a 735/737/739 variation rather than all labelled 739 but there were different physical parts available with the same part ID.

 

[bikeworkshop]

Have you got the right chainring?

The teeth often need to be in exactly the right position for the chain to mesh smoothly when the cranks are vertical.
Consequently there are times when a chainring from a different manufacturer or even chainset causes poor front shifting.

This is why a lot of people think indexed front shifting doesn't work well.

Id suggest lookimg at the shimano exploded diagram and checking you've got the compatible rings.

Iirc 44/34/22 was the combo, so the culprit could be the middle ring

 

[Lou Carpenter]

Simply trying to help, and a pic would identify the part better - I've got a box with perhaps ten XT mechs in it and there are numerous changes between the various types despite all being from the same version of XT. There were top pull and bottom pull versions and, IIRC, both top swing and bottom swing. The latter may have been a 735/737/739 variation rather than all labelled 739 but there were different physical parts available with the same part ID.

Sorry, wasn't trying to cause offence. I can take a pic for you later but I'm in the office at the moment. Yes, sorry I forgot that there was bottom and top pull, mine is a top pull, top swing. I think the M738 was a bottom swing. The problem I'm having may well be a problem also with the M737 crankset, although I couldn't comment, this was also listed with the same two chainring options.

 

[Lou Carpenter]

Have you got the right chainring?

The teeth often need to be in exactly the right position for the chain to mesh smoothly when the cranks are vertical.
Consequently there are times when a chainring from a different manufacturer or even chainset causes poor front shifting.

This is why a lot of people think indexed front shifting doesn't work well.

Id suggest lookimg at the shimano exploded diagram and checking you've got the compatible rings.

Iirc 44/34/22 was the combo, so the culprit could be the middle ring

Yes, the chainrings I have are a set and are aligned correctly, and it is meant to be a 44-32-22 combo.

 

[Lou Carpenter]

I take it this isn't a common problem then? I thought it may have been an oversight from Shimano that was pretty well known about by those in the know? Are there any of you out there running M739 FD's, or even M737 FD's, with 44-32-22 chainrings? I could use a M750 FD but then I'd be moving from shiny silver to painted matt silver which I'm not so keen to do.