In the 1960s, General Motors started manufacturing a new three-speed automatic transmission named the Turbo Hydra-Matic 400 (TH400) that saw first use in 1964. Commonly called the Turbo 400, it was so rugged it instantly became GM's go-to transmission for everything with high-power or severe-duty use. It is estimated more than 10 million units were made before production ceased in the late 1980s. What made the Turbo 400 such a successful transmission was how it optimized the power flow so internal friction losses were minimal, yet it had the brute strength of large clutches and four-gear planetary sets. Fortunately for us off-roaders, GM had the foresight to install it in most of their 4WD fullsize trucks.
What makes the 400 so desirable? It is the last of the old-school fully hydraulic-controlled non-over-drive transmissions. This means no failure-prone electronics or heavy, complicated overdrive gear sets.
As usual, gearheads eventually found ways to subject parts to obscene abuse GM could never have imagined. Think of something like a heavy Blazer on 40s crashing along with the loud pedal buried to the floor; a perfect recipe for destroying even the most rugged transmission. After getting numerous requests for an improved Turbo 400, Reid Racing started doing feasibility studies on making an aftermarket transmission case.
The company's engineers carefully studied failed OEM units. As beefy as the Turbo 400 is, it has one glaring shortcoming: Failure of the lugs that hold the center support and intermediate clutch pressure plate in place. Even without excessive power, these lugs can be snapped off, making the transmission instant scrap.
Extensive discussions have been carried out with many of the major transmission builders in the country. These discussions revealed more problem areas along with wish lists of added features. It quickly became obvious two different versions would have to be manufactured to address specific problems for each type of use—one for drag racing and one for off-road. Most problems were common in all uses, but there were three primary problems unique to off-roading. These were twisting of the case due to chassis wracking, lack of cooling lubrication to the rear gear set (most often seen in desert and short-course trucks), and most importantly, breakage in the tail area of the housing when used with transfer cases.
Existing Turbo 400 parts are 100-percent compatible with the Reid Super Hydra case, so upgrading is a bolt-in operation from your existing GM transmission. If you non-Chevy guys are feeling left out, there's no need to despair; the transmission case has been designed with a bolt-on bellhousing. The transmission can be used behind virtually every popular engine. Seven different bellhousings are available for GM, Ford, and Chrysler motors. All these bellhousings are beefed up so much, they are SFI 30.1 explosion certified and fit 11-inch (280mm) converters. The bellhousing locates off a separate pilot ring on the transmission case and is held by eight heli-coiled bolts instead of mounting to the oil pump. This mounting method ensures perfect alignment and maximum strength.
The cast lugs on the inside of the OEM GM case do not go completely around the inside of the case. To allow economical manufacturing, there is a gap in the lugs that extends about a fifth of the way around the GM case. With high-line pressures and abrupt shifts typical in racing applications, the lugs closest to the gap become overloaded and fail. That sets off a chain reaction and all of the remaining lugs fail in a zipper-like fashion, ultimately resulting in catastrophic failure of the transmission.
Reid Racing addressed this problem by making the lugs go all the way around the inside of the case, which allows the loading to be equally distributed between all the lugs. In addition, a much larger snap ring was custom made. This ring is stiffer for less flex and the groove for it goes into the main body of the case, rather than in just the lugs. This transfers the loads into the housing instead of the weaker lugs.
The problem with lack of case stiffness was solved using many techniques. The first was starting with a phenomenally expensive permanent mold casting technique. Sand castings would be much cheaper, but they are not nearly as strong, tough, ductile, or leak-free. In addition, due to casting core shifts, it would have been impossible to hold the precision casting tolerances needed. The wall thickness was tripled, which not only increased stiffness, but it allows the case to be SFI 4.1 certified for explosions without the need for any external shields. Many trucks already have chassis clearance issues with the transmission case, so the stronger Super Hydra case solves this problem, too.
Cooling and lubrication of the rear gear set has always been a common problem in desert trucks because of constant high horsepower being applied over long periods of time. Now the more aggressive rock racers are starting to see the same effects. The rear gearset becomes extremely hot because not enough oil gets to the rear of the case to cool and lubricate the gears, and they eventually grenade themselves. The Reid Supra Hydra 400 has been designed to accept a GM4L80E center support, which lubricates the rear gear set. A machined boss that taps into the oil cooler return line and a machined boss near the center support have been added. These are connected via an external braided line to supply additional cooled oil to the center support and gear set.
A major weakness in the OEM Turbo 400 cases is a fragile tail section. When a heavy transfer case is hung off the rear of the case, it can break off the back of the transmission. The Reid Racing engineers have addressed this problem in many ways. Instead of individual ears that the transfer case bolts to, the Reid case has a thick flange that distributes the load evenly between all the bolts. This flange is tied into the main body of the case with three massive struts, which again distributes the loading between the tail section and the main body. Lastly, a huge rib runs directly from the bottom of the flange clear through the case until it ties into the valve body area. Case breakage will not be an issue anymore with the Reid case. An added feature is these cases are already pre-machined to accept the popular Atlas transfer case adapter plates. Attaching the transfer case is a simple bolt-on operation.