General Motors TH400

TH400 Transmission Specs & Ratios

The Turbo Hydramatic 400 transmission was General Motor's heavy duty, 3 speed automatic transmission. It first appeared in 1964, where it was used as a production option for Cadillac cars. When the 6.2L Detroit was introduced in 1982, the TH400 was the only available automatic transmission for 3/4 and 1 ton pickups, while the lighter duty 1/2 ton C/K series trucks used the overdrive TH700R4 instead. The TH400 is highly regarded for its strength and reliability, even in heavy duty applications. Years upon years of service have proven the levels of abuse that a TH400 can handle without hesitation.

The transmission is widely popular in drag racing and other high performance motorsports. As a result, there is an abundance of aftermarket support and build options. With only 250 lb-ft of torque, the TH400 was certainly overkill for the 6.2L diesel. In 1987, the TH400 was renamed the 3L80 (three speed, longitudinal, 8000 lbs GVWR) as a result of a change in name convention for all GM transmissions. The heart of the TH400 was the Simpson planetary gearset, use of which was obtained under license. Though obsolete today, the Simpson gearset was revolutionary to the evolution of the automatic transmission, and was also the backbone of Ford's C6 and Chrysler's Torqueflite 727.


TH400 Transmission Ratios





2.48 : 1

1.48 : 1

1.00 : 1

2.07 : 1


TH400 Transmission Specs


Turbo Hydramatic 400 (TH400)


3 speed automatic transmission


General Motors

Model Years/Applications:

1982 - 1990 C/K series pickups (6.2L diesel, 3/4 and 1 ton models)

Case Material:


Max Input Torque:

~ 450 lb-ft


~ 150 lbs w/ ATF

ATF Type/Spec:

DEXRON automatic transmission fluid


• 32 spline output shaft

• Integrated bellhousing