How to Identify a 700 R4 Transmissionby Floyd Drake III
Along with the THM200-4R, General Motors' THM700-R4 automatic transmission was the last of GM's Turbohydramatic transmission series. First introduced in the 1960s, GMs Turbohydramatic transmissions were successors to the Powerglide transmission, and included the popular THM350 and THM400 models. The THM700-R4, first used on the 1982 Chevrolet Corvette, was primarily designed for use on trucks and larger automobiles. Identification of the THM700-R4 automatic transmission is accomplished by locating visual clues separating it from other GM and Chevrolet automatic transmissions and by decoding the information found on the identification tag.
View the transmission pan located on the bottom of the THM700-R4. If the transmission is installed, this requires going underneath the vehicle. Access the transmission by going under the vehicle at the front passenger's side door.
Count the number of bolts holding the transmission pan in place. The THM700-R4 has 16 bolts attaching the pan to the transmission.
Identify the shape of the transmission pan. The THM700-R4 has a nearly perfect rectangular shape, with three rounded corners. This shape is the same as the THM700-R4s successor, the 4L60-E.
Locate the identification tag attached to the transmission. According to Hotrodders, the ID tag is found on the passenger's side of the transmission housing, towards the rear, just above the oil pan. A sample code reads "8YDM021H," with the first digit representing the year. The first year, 1982, is identified by "9," with all following years identified by the last digit of the year. The final year of THM700-R4 production was 1993, which is identified by "3." All GM transmissions from 1982 to 1993 with the same pan shape and 16-bolt count are THM700-R4s, anything later becomes a 4L60-E transmission.
- According to Hotrodder's THM700-R4 identification page, 1982 to 1985 transmissions have a two position letter code following the year code and 1986 to 1993 units have three letters. This avoids confusion when differentiating between 1983 and 1993 transmissions. 4L60-E transmissions have four-position identification code.
- corvette image by Julianna Olah from Fotolia.com