The Difference Between a 2WD & 4WD Transmission


Two- and four-wheel drive automatic and manual transmissions are almost identical in just about every way. They feature the same housing, gear ratios and often – but not always – have the same spline count on the output shaft. Primary differences are the two-wheel transmission output shaft is longer than the four-wheel version and four-wheel transmissions mate to a transfer case. Some automakers build their two-wheel transmissions so they can be converted to four-wheel models.


  • Many car two-wheel transmissions can be converted to truck four-wheel drive, but they are not necessarily ideal for the demands of four-wheeling. General Motors’ automobile transmissions, including the performance Muncie M21 and M22, and Saginaw and Borg Warner T-10, can convert to four-wheel as long as they are not asked to do any heavy knockabout off-roading. The lack of low gears makes transversing rough terrain difficult. Two-wheel truck transmissions, such as the Muncie SM420, SM465 and the NV4500 and NV3500, easily mate with a four-wheel drive transfer case and can handle the demands of rough off-roading.


  • A two-wheel transmission is identified by its long tailshaft with the rear section consisting of an overdrive unit. The four-wheel drive transmission also has a rear overdrive unit section, but it mates with a transfer case that distributes the power to the front and rear axles. Two-wheel transmissions have no transfer case. However, some vehicles like the two-wheel drive Ford Bronco II, have a dummy transfer case to ease conversion to four-wheel drive by only requiring a new output shaft.

Major Differences

  • The GM SM465 and TH350, and Aisin AX-15 transmissions typify some of the differences between two- and four-wheelers. GM produced the SM465 manual transmission from 1968 to 1991 for its half- through 3-ton Chevrolet and GMC trucks and sport utility vehicles. Through 1978, the SM465 two- and four-wheel transmissions featured identical internal parts except for the output shaft. The four-wheel version had a 10-spline output shaft and transfer case. The two-wheel model had a 35-spline output shaft with the conventional two-wheel-style tailhousing. From 1979 to 1991, the four-wheel SM465 featured a shorter 32-spline output shaft. The two-wheel SM465’s 35-spline remained and its internals mirrored the four-wheel version. The TH350 automatic came in both two- and four-wheel applications with the two-wheel versions possessing tailhousings lengths of 6, 9 and 12 inches while the four-wheeler output mated with the transfer case. The AX-15 two- and four-wheel transmissions featured the same internal parts, but the two-wheel version had a 14-spline shaft and the four-wheel has a 23-spline shaft.

Transfer Case

  • The transfer case connected to the rear of the transmission should be a dead giveaway that the vehicle is four-wheel drive. However, the transfer case may be a dummy available for later conversion for four-wheeling. Operating transfer cases connect to the transmission and use two drive shafts to split the power between the front and rear axles. These are a part-time manual transfer case operated by the driver or part-time electronic activated with a switch. Some vehicles, such as sports cars, have full-time permanently locked transfer cases.

Related Searches


  • Photo Credit Thinkstock/Comstock/Getty Images
Promoted By Zergnet


Related Searches

Check It Out

How To Travel For Free With Reward Points

Is DIY in your DNA? Become part of our maker community.
Submit Your Work!