GM has manufactured several types of transmissions over the years. If you need one for a project, knowing what you've got comes in handy. Identifying a GM automatic transmission can be done with a few quick looks and some measurements.
Measure the transmission from the bellhousing to the end of the tailshaft using the tape measure. The 200-4R and TH350 are both 27 inches long. Tthe TH400 is 28 inches, and the 700R4 is 30 inches long.
Look at the shape of the transmission pan on the bottom of the transmission. The 700R4 has a mostly square pan. The 200-R4 has two humps and looks like the state of Idaho. The TH400 looks like the state of Oregon with a small pump on the bottom, and the TH350 looks like a square with a corner cut off and a slight angle at the rear.
Count the number of bolts on the transmission pan. The 4l60 and 700R4 transmissions both have a square pan with 16 bolts.
