How to Identify GM Automatic Transmissions


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.

Things You'll Need

  • Tape measure
  • 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.

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