The THM325 became the THM325-4L with an overdrive added in 1982, but all vehicles using this transmission switched to more-conventional transverse engine mounting in 1986. Bellhousing pattern used the 1967-90 Buick-Oldsmobile-Pontiac-Cadillac V8 pattern throughout its entire lifecycle.
The THM325 transmission underwent a transformation in 1982 with the introduction of an overdrive system and a shift to a more conventional transverse engine mounting configuration was implemented in 1986. The bellhousing pattern remained consistent throughout its existence, utilizing the 1967-1990 Buick-Oldsmobile-Pontiac-Cadillac V8 pattern.