How to Identify the Transmission in a Buick

by Floyd Drake III
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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.

Step 1

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.

Step 2

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.

Step 3

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

Step 4

For further automatic transmission identification, use a Buick transmission application chart such as those found on the Patio Transmissions and Macko Distributing websites.

Step 5

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.

Step 6

For further Buick manual transmission identification, use a Buick transmission application chart such as that available on

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