[Cliff R]

No special fluid is needed, just plain old Dextron is fine in any of these transmissions. Does it hurt to run a custom "blend", synthetic, or something else, probably not but a complete waste of time/funds. I use plain old Dextron III or equivalent in all the units we've built here with zero issues in any area. The key to success is using good parts and getting the shift program nailed down.

Same thing with fancy red, blue frictions and heat treated or kolene steels. Stock Raybestos, Borg Warner and Alto is more than adequate for any power level.

The cost of a rebuild is simple, rebuild parts, upgrades and labor. Since a TH400 does need a lot of help to survive in a high performance environment few "upgrades" are needed, at least costly ones.

A complete/correct rebuild should include steels, frictions, bands, bushings, thrust washers, seals, and gaskets. It may include a shift kit if the builder doesn't do their own "home-brew" deal. So parts easily under $300 for everything needed.

Upgrades. If you have an early trans with a smooth direct drum the 34 element sprag upgrade is under $100 including he spriral lock ring to retain it. If you have later trans with the roller clutch or "notched" drum you'll need to buy a 4L80E drum or smooth TH400 drum. If you go 4L80E might as well outfit in with the steel apply piston with molded seals. So a couple hundreds bucks there depending on what you find and end up with.

So we're up around the $600 for parts if you needed the direct drum replacement. Next add for any worn hard parts, or upgrades. Then add labor and if you didn't need any hard parts replaced your build should EASILY come in well under $1000. Most of the builds I've done here were around $700-900 parts and labor. Expect to spend $600 or so on a good converter, but you can cheap out there and still keep the entire job under $1000 without much effort.

Why and how folks are spending $1400-2500 or even more for TH400 "builds" is beyond me, unless they are buying into some BS about how they need billet internals and expensive upgrades to a trans that will EASILY handle big power without them. Also keep in mind that there are a LOT of "builders" out there that buy a $30 seal/gasket kit and outfit everything inside your trans from nicely used/sanded steels, frictions and bands they have hanging on nails around the shop removed from other units they've torn down over the years. Your shift "kit" is nothing more than drilling a couple of holes in the separator plate, shimming the PR valve, leaving off a sealing ring and blocking a feed hole in the case. So basically you could pay $1000, $1400 or even more for a $30 effort and never know it.........Cliff