So I have an old hybrid frame that I want to build up into a halfway decent cross bike. The frame has standard MTB spacing and BB. Here's what I'm thinking for a decent 2x10 setup:

FSA afterburner crank 42-30 (Shimano 10-spd compatible)
Shimano XT 10spd front derailleur
Dura Ace 7801 10spd/double shifters (that I have floating around)
Shimano XTR 9-spd rear derailleur (couple years old that I have floating around)
Shimano XT 10 spd cassette

From what I can tell, you can use Shimano road shifters with 10spd MTB front derailleur but they won't work with dyna sys 10spd MTB rear derailleurs. That's why I'm suggesting the 9spd rear derailleur instead which I have heard does work. One thing I'm not sure about is whether the 9spd derailleur works in a 10spd system. I KNOW you can do it a 9spd system (with the dura ace shifters) because I've done it. Does anyone know if the above system will work (or have any other comments)?

Thanks!

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The cardinal sin: put drop bars on a frame meant for flat bar or vice versa. Big NO.

Otherwise, it more or less works.

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Elviento has a good point.
I have recently built 2 bikes to this principle; a drop bar MTB and a friend's hybrid (Scott Sportster) converted to a drop bar touring bike.
As you said it was an older hybrid frame, you won't have disc caliper issues, but the front XT derailleur will not work with the shifters.
After a LOT of p***ing around with an Umlenker and various MTB derailleurs to acheive the required top pull, I finally settled on 2 different solutions.
For my friend's Scott I used an Ultegra front derailleur with a pulley down below and FSA Vero compact cranks. Rear derailler is a Microshift long cage MTB.
On my bike (Mosso MTB) I bought a Microshift MTB derailleur, hacked it apart and drilled a new anchor point for the cable. It works perfectly and only cost $13 and a bit of sweat. This runs with An FSA carbon MTB crank (2x9). The rear derailleur in this case is a 105 short cage.
The easiest setup to build is the pulley method. Forget the Umlenker unless you are able to run road cranks with a standard double bottom bracket, anything more puts the derailleur cage positon so far out that the Umlenker is no longer pulling at the right ratio.
The XTR rear should work with the shifters as you said it was 9 speed. A 9 speed RD will work in a 10 speed system, but the reverse is not always true unless a 10 sp chain is used.
I'll post up a photo of the Scott setup tomorrow (and see how long it takes someone to paste it into the Freaks thread).
Best of luck, and Happy Bodging

Monkeyburger

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No, it isn't an ideal 'cross solution, but it is great for off-season training. I have been running an MTB with Record and drop bars for years. You can replicate your road position and run your FrankenBike all winter.

This bike was meant to take drop bars and always has had them so we're okay there. I'm not even going to change the bars.

Still concerned about the front shifting though. Can I use an Ultegra front derailleur instead? Also if I do that which would be better: a 10 spd dyna sys crank or an older 9spd double front crank? (I know the spacing is slightly closer on the 10spd dyna sys but I don't know which matches the road cranks better.)

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A long time ago, I ran an MTB drop bar Frankenbike with a 36/48T Deore DX triple (run as a double) and Deore LX front derailleur, paired with STI shifters.

Front shifting was mostly fine, occasionally requiring an extra nudge on the shifters. So my advice would be to at least try it with the XT front derailleur.

I can't see an issue with an XT FD, it's desigend for 32->42 as a stnd MTB triple, so can't see it not working fine on 30-42.

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The XT FD will work with the crank admirably. The problem is that MTB FDs pull at a different ratio than Road FDs. It is possible that the XT will shift a double, but you will probably need to set it up with a certain amount of cable slack at innermost stopped position and be very careful as to the uppermost limit position and cage positioning as the trimming will be lousy. At least that is what I found having been down this road before.
To the OP, if this bike originally had drop bars is it bottom pull at the FD. If it is top pull, do you not have the original FD?
Sub par FD clearance at crossover can be improved by running a 10 speed chain. This can be an issue if using FDs with deeply profiled cage shapes if the chainring sizes are changed away from those for which the FD was designed.
When buiding drop bar mtbs I thought cranks and braking would be a hassle, but they are a cinch compared to the PITA front shifting...
Monkeyburger.

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Why not just buy a FD which matches the shifter lever pull? 105 or something will be fine so not expensive.

I like Frankenbikes - reminds me of Tomac.

Check reach on your frame - most flat bar / MTB frames are 70mm longer than the equivalent size road frame so you'll be pretty stretched out or need to run a stumpy stem.

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