How to Identify the Transmission in a Buickby Floyd Drake III
A variety of automatic and manual transmissions have been used on Buick vehicles. Buicks are normally equipped with a General Motors Buick, Oldsmobile, Pontiac (BOP) transmission. This is essentially a Chevrolet transmission adapted to suit the particular requirements of these brands. The easiest way to identify a Buick automatic transmission requires you to examine the transmission oil pan; manual transmissions have their own visual characteristics.
Determine whether your transmission is automatic or manual, and if your Buick is front- or rear-wheel drive. Access the transmission if it is still installed in the vehicle. For rear-wheel-drive vehicles, access the transmission from underneath the driver-side front door. For front-wheel-drive vehicles, the transmission is normally located on the passenger side of the car and in front of the right front wheel.
Count the number of oil pan bolts on the bottom of the automatic transmission. For Buick rear-wheel-drive automatics, the TH250/350 RWD has a 13-bolt oil pan, the TH200 has an 11-bolt oil pan, the TH400 has a 13-bolt oil pan and the ST300 has a 14-bolt oil pan. For front-wheel-drive automatics, the 440T4 has 19 bolts, the 4T60 and TH125 both have 16 bolts and the TH325 has 15 oil-pan bolts.
Use oil-pan shape to differentiate automatic transmissions with the same bolt count. Both the TH250/350 and the TH400 have 13 bolts, however, the TH250/350 has a square pan with one angled corner, whereas the TH400 has an irregularly shaped pan with a bulge on the passenger side of the transmission. The 4T60 and TH125 both have 16 bolts, but the 4T60 has a square pan while the TH125 oil pan has a very irregular shape
For further automatic transmission identification, use a Buick transmission application chart such as those found on the Patio Transmissions and Macko Distributing websites.
Identify your Buick's manual transmission. Muncie M20/M21/M22 four-speed rear-wheel-drive transmissions have a seven-bolt side cover where the shifting linkage connects to the transmission. The Muncie M22 is a larger model, typically installed with high-torque, big-block engines. The GM Saginaw transmission is similar to the M-Series, however the reverse gear lever is attached to the seven-bolt side cover, whereas the Muncie models have the reverse lever attached to the transmission tail housing. Buick also used Isuzu-manufactured manual transmissions. The MR2 is a front-wheel-drive four-speed with an aluminum case. The MR8 is a five-speed transmission with a seven-bolt tin cover on the rear of the transmission. The HM282 is a five-speed transmission with a nine-bolt rear cover.
For further Buick manual transmission identification, use a Buick transmission application chart such as that available on drivetrain.com.
- The majority of transmissions found on Buick vehicles are automatic; manual transmissions were reserved mostly for compact models and 1960s sport-performance models.
A native of New Haven, Conn., Floyd Drake III began writing in 1984. His work has appeared in the "New Haven Register," Medford's "Mail-Tribune" and the "Ashland Daily Tidings." Drake studied journalism at Southern Connecticut State University. After working as a reporter in Oregon, he is now based back home in New Haven.