Shimano Deore Derailleur query

[drystonepaul]

I run 'modern' XT 770ish (2010 era Shadow mechs)

The XT M770 mechs were the last of the 9 speed XT mechs before the M780 series introduced 'Dyna-Sys' 10 speed with a different pull ratio and double pantograph mech configuration.
You can still get M770 mechs as well as the Deore M590/591/592 mechs which are all 9 speed mechs and therefore backwards compatible with 6, 7 and 8 speed shifters and cassettes.

You can also use 9 speed mechs with all the Shimano 10 speed road brifters because they use the same cable pull ratios.
This is good for using MTB mechs on gravel bikes for example, although the older ten speed road shifters aren't that great due to the internal cable routing. But I digress.
This is true up until the latest Tiagra R4700 10 speed shifters which use much improved the 11 speed pull ratio.

This opens the possibility of using any 6, 7, 8, 9 or 10 speed road mechs (except Tiagra R4700) on older road and MTBs.

Basically, Shimano stuck with the same 2:1 pull ratio and double panto arrangement on almost all their rear mechs and shifters up until the introduction of 10 speed for mountain bikes and 11 speed for road bikes.

There are some exceptions on one of the earlier Dura Ace groupsets but I can't remember exactly which one.

 

[ishaw]

Great info. Can I swerve off topic slightly and ask if you know what mtb rear mechs work with 9sp road levers?

 

[drystonepaul]

Great info. Can I swerve off topic slightly and ask if you know what mtb rear mechs work with 9sp road levers?

In theory any of them as specified in my previous post, because they will have the same pull ratio configurations. Even the latest 9 speed R3000 Sora shifters I believe have the same 2:1 ratios.
The only thing you definitely need to stick to is 9 speed shifters with 9 speed cassettes, 8 speed shifters with 8 speed cassettes etc. The rear mech mostly doesn't mind which shifters it's connected to. Front mechs can be a little more problematic though, as in road shifters are normally configured to use road front mechs.
I have got a cross bike with 9 speed 105 5500 shifters (circa 2002) paired with a 9speed Deore M592 rear mech (circa 2014) which all works very well. The front mech is a 105 road mech.

I can't guarantee everything will all be crisp and perfect given the vagaries of older worn components, but from a mechanical perspective the answer to your question is yes.

Cue a load of drop bar conversions.

 

[ishaw]

Thats the plan (drop bar conversion). Probably going 1x so not fussed about front mech. Sounds like I can get away with any 9sp rear so that's good as have plenty.

Cheers