I'm frankenbiking a 2005 JTS frame with a 1989 Deore DX drive train from a DB Apex. The original DX front derailleur didnt fit the seat tube so I got a 2012 XT front derailluer to use. The indexing seems off a little or it could be my inexperience. Should the old shifter work with the new derailleur?

Using a '10 speed' or Dynasys derailleur won't work. Just get an 8 or 9 speed alivio, deore, xt etc derailleur.

Also make sure the cable is fixed in the groove correctly.

- Joel

Just get an 8 or 9 speed alivio, deore, xt etc derailleur

It's a 3x7, and the XT front is a 3 speed that came off a 3x7 bike. There's sufficient range. Not sure what I need to look for.

Dynasys has utterly ruined cross-compatability over groups, but dynasys is more about the rear shifting. And, of course, other wretched crap, such as directional chains . My main concern would be that the front paralellogram will be too narrow for whatever chain you're using. But, I also suspect that you may be running into trouble as regards a top-swing/bottom swing incompatibility issue....

But, wait, the XT front came off a 3x7 bike? Or a 3x10?

3x7
Every part of the drive train including the chain and cluster was transplanted from a DB Apex. The only odd piece is the XT front.

I'm confused. The DX stuff came from the DB, and it's 3x7. That makes total sense. But the mismatched XT front is a 2012, and it came from a 3x7 bike too?? Or it's designed for a 3x10, and you bought it new?

Isn't 1989 kind of early for indexed front shifting? I would switch it to friction mode if possible.

1989 should be standard drive, all current MTB parts are compact, and have been since around 1992ish, so a 2012 XT FD probably wouldn't even have the correct T count on the crank; then there is the issue of is the XT FD a 2x or 3x as you haven't mention this.

For indexing, pretty sure I had a Rapidfire (not current Rapidfire+) STI on a bike from around this time which was indexed.

For direction chains, were talking MTB, so it's a non-issue.

What size is your seat tube O.D.? I might have a derailleur that fits. PM me.

I had a '90 DB Apex I bought new, and the index shifting, front and back, was impressively good. To me anyway. That was the reason I jumped on a garage queen for $125, for it's DX components. I get some funny looks, (flat bars on a cross bike), but I like the configuration.

That might be the issue right there. The crankset is 46-36-24. I don't think it's the compact variety.

How does the FD cage look against the big ring?

Seems fine. The cage looks to have a somewhat larger diameter than the big ring.
I have to see if the co-op is open today. Might get an expert to look at it.