by Robert Bayly
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The General Motors TH 350, introduced in 1969, was developed by Chevrolet and Buick. It was used in GM cars and trucks until 1984 with small-block engines. The TH400 transmission was first used in 1964 in Cadillac and Buick automobiles. GM’s other brands got the TH400 in 1965. The TH400 was used in passenger cars until 1982 and trucks until the early 1990s. Both transmissions are noted for their strength and durability, but the TH400 is the strongest of the two. There are numerous replacement parts and complete units available from a large number of suppliers.
Park the vehicle on a level paved surface and set the parking brake. Raise the front of the vehicle and support the front with jack stands.
Measure the gearbox with a tape measure. The Turbo 350 body measures 21 3/4 inches long from the front of the hood to the rear of the case. Do not include the tailshaft housing that bolts to the rear of the box. The Turbo 400 is 24 3/8 inches long from the bell tower to the rear of the case.
Look at the driver’s side of the transmission. The Turbo 350 has a “kickdown” cable attached to the right side connected to a manual link in the transmission. The Turbo 400 has an electrical switch.
Look at the transmission tray. The Turbo 350 has a basically square tray with one corner cut off. It actually has five sides. It measures 13 1/2 inches long and 13 inches wide. The Turbo 400 skillet is longer than it is wide. The part of the pan at the rear of the transmission looks like the bottom of the state of Texas (actually). Measures 16 5/8 inches long and 13 inches wide.
Articles will need
- Jack stands up
- Measuring tape.