T-18
Forward gearing: 6.32, 3.09, 1.69, 1.0
Approximate length: 11.87-inch
Output shaft: Varies (Ford 35- or 28-spline 2WD short and long and 4WD). Jeep used several 6-spine output shaft lengths.
Found in: '66-'84 Ford trucks, '65-'87 Jeep FSJs, and some CJs.
Aftermarket support: Adapters, conversion bellhousings (for Ford versions), and internal replacement parts.
Notes: Jeep used literally 14 different versions of this transmission, each with slightly different configurations of input and output stickout lengths and gearing. Both 4.03 and 6.32 First gear are available and input shafts are usually on the long side. Ford used three different versions (look for input stickout length of 6.5inches) and shares the same bellhousing bolt pattern as the Jeep T-150 and T-176 transmissions. If you're looking to swap, the Ford version is easier to find and has more support, but the Jeep version can be used in a long-wheelbase vehicle behind an AMC V-8 and a Quadra-Trac or Dana 20 T-case without too much fuss.
SM465
Forward gearing: 6.54, 3.57, 1.57, 1.0
Approximate length: 12-inch
Output shaft: Short, 10-spline ('68-'79 4WD mated to NP203 and NP205); short, 35-spline (2WD); long, 32-spline ('80-'88 4WD mated to NP208).
Found in: '68-'88 1/2- to 2 1/2-ton GM trucks.
Aftermarket support: Anaheim Gear (800/477-1103, www.anaheimgear.com) offers upgrade parts to cure tendency to jump out of Third gear, internal rebuild components, adapters, and conversion bellhousings.
Notes: Identify by heavy webbing on the driver side and six-bolt PTO cover on both sides. At roughly 175 pounds, it's 40 pounds heavier than SM420 or NP435 and 30 pounds more than T-18. Relatively easy to find nowadays. Larger input retainer requires 5 1/8 bellhousing bore compared with 4 11/16 bore of SM420.
SM420
Forward gearing:7.05, 3.57, 1.70, 1.0
Approximate length: 10.43-inch
Output shaft: 10-spline
Found in: '47-'67 GM trucks.
Aftermarket support: Several different adapter types and replacement internal parts.
Notes: Becoming slightly harder to find good, usable units. Look for 2WD version with bolt-on rear yoke for easy adaptability. Identified by six-bolt PTO cover on driver side and rounded bulge on passenger side. Drain plug points toward rear axle and shift tower is iron.
NP435
Forward gearing: 6.69, 3.34, 1.79, 1.0
Approximate length: 10.875-inch
Output shaft: Ford 28-spline or Dodge 23-spline.
Found in: '70s and '80s Ford trucks as well as '70s through mid-'90s Dodge trucks.
Aftermarket support: Some adapters and bellhousings available for Ford version, very limited T-case adapter availability for Dodge version, and internal replacement parts.
Notes: Aluminum shift tower/top cover is dead giveaway. While Ford version enjoys more popularity, Dodge version is more easily found and has same 23-spline output shaft and round six-bolt adapter mount as most chaindriven Jeep T-cases. Strong and durable tranny.