The Chevy Turbo Hydramatic 400 (Turbo 400 or TH400) is the quintessential three-speed automatic transmission. In a time when 4x4 manufacturers are building transmissions from four-, five-, and six-speed on up to nine-speed, these archaic three-speeds are still considered the go-to trans by off-roaders looking for a tough-as-nails slushbox.
We’re not going to downplay the strength of the 400’s three-speed cousins, the Ford C6 and Dodge TF727, but the 400 has, like the GM V-8, a lot more aftermarket support. We have seen the 400 swapped behind many different engines and inside every type of race vehicle, from mud bogger to rockcrawler to Trophy Truck. The TH400 is strong and simple, there’s no computer to get confused and no additional wires or garbage to worry about, and it can get even better with a high-performance valve body. Plus, with new developments by the aftermarket the TH400 just keeps improving.
The latest upgrade offered for the TH400 is the new Super Hydra 400 case from Reid Racing. The TH400 was offered with a variety of cases depending on the original application (car, truck, heavy-duty truck), but this new Reid case steps beyond even the toughest factory case to offer increased strength, dependability, and rigidity to help transfer power to the ground from even the biggest powerplants under the hood.
We recently visited Rancho Drivetrain Engineering to follow along as they built a desert-racing performance transmission. Then we tried our hand at building a trail rig version of our own. With a 400 like this you’ll be dreaming of more motor in front of it.
We realized that we didn’t need a full-blown Trophy Truck transmission for our rockcrawler, but we wanted to upgrade from the old 700R4 to a beefy 400 in anticipation of more horsepower. We sourced a Reid Racing SH400 case as well as a complete set of clutches, steels, and Kevlar bands and a deep pan from Summit Racing Equipment. We also purchased a 4L80E direct drum with straight-cut planetaries and the center support. From Rancho Drivetrain we got the billet forward hub and drum with 300M input shaft and the company’s unique reverse manual valve body, the only one we could find with compression braking.
We took all these parts and a used TH400 from our old Project Army Truck and headed to Aaron’s Advanced Automotive for the assembly. Aaron Runyan lent us a hand and gave instructions while we assembled a transmission for our crawler. Building a TH400 isn’t impossible for a rookie transmission builder, but it’s not a bad idea to purchase a how-to DVD from Summit and/or find an experienced trans builder willing to teach you the ways of the slushbox.