page_title: Turbo-Hydramatic 425
hierarchical_section_title: Turbo-Hydramatic 425
caption_attribution_description: English: A 1965-78 THM 425 transmission at the Ypsilanti Automotive Heritage Museum in Ypsilanti, Michigan (United States).
context_page_description: Turbo-Hydramatic 425 was an automatic transmission developed and produced by General Motors. The THM425 was a derivative of the THM400; most parts directly interchange and some others will interchange with minor modifications. The internal parts spin the opposite direction in the THM425; the helical angle of the planetary gears is "reversed" and the one-way clutches freewheel in the opposite direction, for example. The THM425 was developed for the 1966 Oldsmobile Toronado and the 1967 Cadillac Eldorado. A lighter-duty transmission known as the THM325 replaced the THM425 in both car lines after the 1978 model year. 1979 and later longitudinal engine front-wheel drive vehicles used the THM325. 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.
  Applications:
  THM425
  1971-1979 Cortez Motor Home
  1966–1978 Oldsmobile Toronado
  1967–1978 Cadillac Eldorado
  1973-1978 GMC Motorhome
  1973-1978 GMC TransMode multi-purpose vehicle
  1972-1978 Revcon motorhome
context_section_description: Turbo-Hydramatic 425 (and later 325) was an automatic transmission developed and produced by General Motors. The THM425 was a derivative of the THM400; most parts directly interchange and some others will interchange with minor modifications. The internal parts spin the opposite direction in the THM425; the helical angle of the planetary gears is "reversed" and the one-way clutches freewheel in the opposite direction, for example. The THM425 was developed for the 1966 Oldsmobile Toronado and the 1967 Cadillac Eldorado. A lighter-duty transmission known as the THM325 (using components sourced from the THM200) replaced the THM425 in both car lines after the 1978 model year. 1979 and later longitudinal engine front-wheel drive vehicles used the THM325. 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. 
  Applications:
  THM425
  1971-1979 Cortez Motor Home
  1966–1978 Oldsmobile Toronado
  1967–1978 Cadillac Eldorado
  1973-1978 GMC Motorhome
  1973-1978 GMC TransMode multi-purpose vehicle
  1972-1978 Revcon motorhome
  1989–1993 Vector W8
  THM325
  1979–1981 Buick Riviera
  1979–1981 Cadillac Eldorado
  1979–1981 Oldsmobile Toronado
  1980–1981 Cadillac Seville
  THM325-4L
  1982–1985 Buick Riviera
  1982–1985 Cadillac Eldorado
  1982–1985 Cadillac Seville
  1982–1985 Oldsmobile Toronado
caption: A THM 425 transmission, produced between 1965 and 1978, at the Ypsilanti Automotive Heritage Museum
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