coupled behind the small block V8s such as the 283 ci engine, and the third-generation inline six-cylinder engine and inline four-cylinder engines. By the late 1960s, demand for two-speed automatic transmissions was dwindling as buyers were demanding three-speed units (Ford, Chrysler and American Motors had already switched entirely to three-speed automatics by this time). In 1969, the three-speed Turbo Hydramatic 350 (THM350) was introduced as a light-duty companion to the Turbo-Hydramatic 400, and made available on virtually all Chevrolet cars and trucks with six-cylinder or small and medium-sized V8 engines, as well as intermediate sized cars of other GM divisions. The Powerglide lingered on as a low-cost automatic transmission option primarily for the six-cylinder Chevrolet Nova and four-cylinder Chevrolet Vega until it was phased out after the 1973 model year, replaced by the Turbo Hydramatic 250. They were also used in the DJ-5 'Dispatcher' Jeeps sold for light commercial use, and best known for their service with the US Postal Service. Its simple and robust design has led drag racing enthusiasts to work with it, giving the Powerglide an effective service life of nearly five decades past its intended obsolescence. Types There were two primary types or versions of the Powerglide: the Powerglide transmission introduced in 1950 had a cast iron case and is known as the "Cast Iron Powerglide", used until 1963, when it was revamped as "Aluminium Powerglide" where its case and several of its other parts were made of aluminium. Early models were air cooled, and later 60's versions used a fluid cooler in the radiator. The Aluminium Powerglide, and Tempestorque was used from 1962 until it was replaced with the Turbo-Hydramatic series of transmission in 1973. The Aluminium Powerglide is still used today as a racing transmission of choice by many racers mainly for the fact that it only shifts once, and for its extreme durability. It is also possible to purchase all the parts needed to build an Aluminium Powerglide from scratch from most racing parts vendors. Torque-Drive For the 1968 model year, Chevrolet introduced a semi-automatic version of Powerglide marketed under the name Torque-Drive. This unit was basically Powerglide without the vacuum modulator, requiring the driver to manually shift gears between Low and High. The quadrant indicator on Torque-Drive cars was, Park-R-N-Hi-1st. The driver would start the car in "1st," then move the lever to "Hi" when desired. Torque-Drive was only offered on low-horsepower