The TH350 and 700R4 are some of the most popular General Motors automatic transmissions available. Both transmissions are for use in rear-wheel drive cars and trucks. The 700R4 utilizes four forward gears with a lockup torque converter that offers better fuel mileage. The TH350 transmission only features three forward gears. Knowing the main physical differences between the two transmissions will enable you to determine any modifications you might need to do when performing a transmission swap or finding a suitable replacement for your vehicle.
Measure the length of the transmission from the bell housing to where the tail shaft mates to the unit. The bell housing is the large rounded end of the transmission, and the tail shaft features a small U-shaped yoke at its end. The TH350 measures 21-5/8 inches, and the 700R4 measures 24 inches from the end of the bell housing to where the tail shaft mates to the unit.
Examine the shape of the fluid pan located on the bottom of the transmission. The TH350 transmission fluid pan is square in shape and appears to have one corner cut off with 13 mounting bolts. The 700R4 fluid pan has a solid rectangle shape and 16 mounting bolts.
Look on the driver’s side portion of the transmission for an electrical connector for the 700R4’s lockup torque converter. The TH350 transmission does not have this connector.
