See Figures 1 and 2
All Buick, Oldsmobile and Pontiac models covered in this guide use various GM Turbo Hydra-Matic (THM) automatic transmissions. Transmission identification numbers are found on either side of the transmission case, depending on model. Some models also have I.D. numbers stamped on the governor cover.
Buick models are equipped with the 200, 200C, 200-4R, 350, 375B and 400 transmissions. Oldsmobile uses the 200, 200C, 200-4R, 250, 350, 375B and 400 units, and Pontiacs are equipped with the 200, 200C, 200-4R, 350, and 400 transmissions. The 375B transmission was last used in 1976, while the 200-4R was introduced in 1981.
A quick way to visually identify the transmissions is to look at the shapes of the pans. The 250, 350 and 375B have a squarish pan with the right rear corner cut off. The 200 pan is similar but more rectangular. The pan of the 400 model transmission is irregularly shaped.
The 200, 250, 350 and 375B models are also identified by their kickdown linkage, which is actuated by a cable attached to the accelerator pedal linkage. The 400 model transmission has an electric kickdown connected to a switch on the accelerator linkage.
The 200 model transmission was first used in 1977 and is the first all metric unit built by GM in the U.S. This transmission sometimes has the word METRIC stamped on the pan. The 200-4R model is an automatic overdrive version of the 200 transmission. The 200C, 250C and 350C transmissions are similar to those given these number designations without the C except that they incorporate a lockup clutch in the torque converter.
There is little visual difference between the 350 and 375B transmissions, except that the latter has a longer output shaft and extension housing.