How to Identify a Turbo-Hydromatic Transmissionby Floyd Drake III
Chevrolet's Turbohydramatic transmission line is the next transmission progression from the Chevy Powerglide, a reliable transmission first offered in the 1960s. When the Powerglide could no longer be improved upon, the THM series was developed. The hydraulically operated THM series consists of the THM700, THM400, THM350 and the smaller THM200, used mostly on four-cylinder engines. For many years the THM series was Chevrolet's premier automatic transmission and was used on a wide array of vehicle applications. Identification is accomplished by counting the transmission pan bolts and identifying the pan shape.
Crawl under the vehicle to identify the transmission, if it is still installed. The pan is located at the bottom of the THM transmission, bolted to the transmission housing.
Notice the pan shape. Each Turbohydramatic has a unique gasket shape and each is illustrated on the Chevrolet Car Club of Victoria's identification page. Both the THM400 and 200 have irregular-shaped pans, while the THM700 is rectangular and the THM350 is square with one corner on an angle.
Count the number of bolts attaching the pan to the THM transmission. The THM700 has 15 bolts, the THM200 has 16, and the THM400 and THM350 both have 13 bolts. The difference between the two is the pan shape.
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