Turbo 400 Transmission

Turbo 400 Transmission

The Turbo 400 transmission (also known as the Turbo Hydramatic 400, TH400 or later as 3L80) is arguably one of the most popular 3 speed automatic transmissions of all time. It can be found in tons of hot rods, race cars, and other vehicles.

The turbo 400 transmission is basically the heavy duty version of the turbo 350.  In stock form it is designed to be able to withstand the horsepower that performance machines can be put out, and it still works great behind milder V-8’s.  You can find the turbo 400 transmission in configurations that range from use to the extreme street.

It was first introduced in 1964 Cadillacs and Buicks (under the guise of Super Turbine 400). It quickly was expanded to several other GM brand names. It was often found bolted to the most powerful engines that the manufacturers had to offer. During its early development stage it was often regarded as a three speed Powerglide due to its similarities to the original powerglide transmission. 

The turbo 400 transmission was nearly completely phased out by 1980. Due to the increase in oil costs they were being replaced with transmissions that provided an overdrive gear such as the 700R4 or 200-4R. The last known car to have a TH400 in it was president Reagan’s limo. It was slowly phased out of the pickups and vans as well and was more less completely phased out by 1986. The only vehicle that is produced with this transmission today with a version of the Turbo 400 transmission is the US Army HUMVEE. 

The turbo 400 transmission was available in both a 4x4 and a two wheel drive varieties.  The difference is primarily in the outputs.  The gear ratio for the TH400 is first gear at 2.48:1, second gear at 1.48:1 and third gear at 1.00:1.  

This is a very popular and desirable transmission for the automotive competition industry due to their great strength. One of the main reasons it is so much stronger then it’s smaller brother, the turbo 350, is because it has a cast iron center support that helps suspend the transmission’s concentric shafts. 

There really weren’t many major changes that happened to the turbo 400 transmission during its run, so there generally isn’t one year that’s more desirable than another. 

Turbo 400 Transmission Identification 

The TH400 is a two piece cast aluminum alloy.  One for the main transmission housing and fixed bellhousing, and a second for the tailshaft (tailshafts not installed on 4wd variety).   

A Turbo 400 transmission can easily be identified by its transmission pan shape (which can be seen in the third picture above), which is often described as being similar to the shape of Texas..  It is also recommended that you get the version of the transmission that you ultimately want (4x4 vs 2x4) since you will otherwise pay additional money to convert it from one type to the other. 

Overall it’s a great transmission, and some aftermarket specialist claim that with the right upgrades it can handle up to 2000 HP