How to Tell the Difference Between a Turbo 350 & a Turbo 400

by Cayden Conor

The turbo 350 and turbo 400 are GM transmissions that were used from 1969 through 1979 for the TH-350 and 1964 through 1990 for the TH-400. The TH-350 was a low-torque transmission that was used in heavy cars. With modification, the TH-350 could be used as a high-torque transmission in a light car. The TH-400 was a high-torque transmission that was used in heavy cars --- it was a much stronger transmission than the TH-350.

Locate the vacuum modulator. On the TH-350, it is located on the right front of the transmission. On the TH-400, it was located on the right rear of the transmission. Also, the TH-350 had a kick down cable, while the TH-400 did not. Both were designed to be used in Chevrolet V-8 cars and light trucks.

Look at the transmission pans on both transmission. Both transmission pans have 13 bolts, but they have a different shape. The TH-350 uses a square pan, with one corner cut off. The TH-400 uses an oblong-shaped pan with one side having a "hump" in the pan and one side is curved while the other two sides are straight. The TH-400 pan also has two circular indentations on the humped side of the pan.

Measure the transmission. The overall length of the TH-400 is 38 inches, while the overall length of the TH-350 is 33 5/8 inches, if both use the longest tail shafts available. The TH-400's body is 25 inches and the TH-350's body is 21 5/8 inches long. The tail shafts for the TH-350 are available in 6-, 9- or 12-inch lengths and the tail shafts for the TH-400 are available in 4-,9- or 13-inch lengths.

About the Author

Cayden Conor has been writing since 1996. She has been published on several websites and in the winter 1996 issue of "QECE." Conor specializes in home and garden, dogs, legal, automotive and business subjects, with years of hands-on experience in these areas. She has an Associate of Science (paralegal) from Manchester Community College and studied computer science, criminology and education at University of Tampa.