bakerjw

I'm building up a new mountain bike with all Deore XT Dyna-Sys components. It's going to be a 2x10 set up and I have everything except for the front derailleur. The compact crank is a 28/40 but I might drop the 28 to a 26 down the road to get a little more on the bottom end. This is a cross country/touring bike which will be carrying gear along with myself. In the Deore XT line, there are 4 clamp on options available and since the bike is a hardtail I can go with top or down swing.

M780 a top swing FD. Shimano doesn't say whether it is a 2x or 3x derailleur.
M781 - specifically referred to as a 3x downswing FD.

M785 a top swing FD. Shimano doesn't say whether it is a 2x or 3x derailleur.
M786 - specifically referred to as a 2x downswing FD.

Are the 780 and 781 for triples and the 785 and 786 for doubles or compacts?
They are all top or bottom pull capable.

As with everything, one model is bound to be preferred over the other. I would lean toward the downswing as it seems to lift the chain more when actuated to the larger sprocket. But the top swing mounts lower and is a bit protected by the compact.

Any thoughts as to one or the other?
Thanks

cobba

Each of those model numbers you listed have variations too.

On the following link click on MTB, > Front Derailleur, > Deore XT , > Submit

You'll see side by side lists of the specs for each derailleur.

https://productinfo.shimano.com/specifications.html

bakerjw

Now that is a very good link! Thanks.

I still wonder which is a more effective design. The top swing or down swing.

headloss 

I think it has more to do with clearance, particularly on frames with full suspension... one isn't more effective than the other, as far as the ability to shift.