We know we'll get hate mail from those of you whose favorite transmission was left out of this story. Deal with it. They're Jp's favorite swaps based on our experience driving these transmissions. And even at that, some of our personal faves didn't make the list after a few heated staff meetings (sorry, Pete). So regardless of personal preference, here are 13 swappable transmissions for your Jeep.
TH400
Forward gearing: 2.48, 1.48, 1.0
Approximate length: 24.25-inch
Output shaft: Long, 32-spline version found in 2WD car and truck or mated to NP205; medium 32-spline version mated to NP208; short 32-spline version mated to NP203 (shown, left to right).
Found in:GM cars and trucks, Jeep FSJ pickups and wagons, and Jeepster.
Aftermarket support: Everything from adapters, low-range First gearsets, billet shafts, convertors, shifters, and so on.
Notes: Jeep cases redesigned in 1974 with AMC-specific bellhousing and case. Way strong and capable of handling severe abuse and big power. Most internals same as GM version. Oil pan shape can cause driveshaft interference with some passenger-side drop T-cases. Length a little long for vehicles with wheelbase around 85 inches or less.
TH350
Forward gearing: 2.52, 1.52, 1.0
Approximate length: 21.50-inch
Output shaft: 27-spline; 4WD versions have stickout length of 1-inch past back of tranny case; 2WD used three different tailhousings with 6-, 9-, or 12-inch stickout length past back of tranny case.
Found in: '69 to late-'80s GM cars and 1/2-ton trucks.
Aftermarket support: Very strong with adapters, upgraded internal components, new shafts, and so on.
Notes: Like the TH400, pan shape can interfere with front driveshaft on some passenger-side drop applications. Tranny takes much less horsepower to spin and is 15 pounds lighter compared with bigger TH400, but can be built to withstand abuse and power. Shorter length, cheap price, and incredible aftermarket support make it an excellent swap alternative.
TF727/TF999
Forward gearing:2.40, 1.47, 1.0
Approximate length:16-inch
Output shaft: 23-spline flush with back of transmission case.
Found in: '80 through '90s FSJ (TF727) and '80s-'03 CJ and Wrangler behind 4.2L and 4.0L engines.
Aftermarket support: Moderate smattering with adapters, converters, some shifters, and internal parts.
Notes: The TF999 has an electronically controlled lockup converter that drops highway engine speed by approximately 150 rpm. Both are very good swap candidates for rockcrawlers or off-road rigs with short wheelbases. Don't confuse with the less impressive 60-degree GM bellhousing pattered TF904 found behind four-cylinder engines.
TH700R4/4L60E
Forward gearing: 3.06, 1.625, 1.0, 0.70
Approximate length: 23.37-inch
Output shaft: 27-spline; 4WD have short shaft with 3-inch stickout length past back of tranny case; 2WD have longer output shaft that must be replaced with 4WD shaft.
Found in: '82 through early '90s GM cars and trucks ('93-and-later are electronically controlled versions named 4L60E).
Aftermarket support: Electronic torque-converter lockup controls, TV cables, shifters, internal parts, adapters, and so on.
Notes: Available in both 90- and 60-degree GM bellhousing patterns so it could be used behind 2.5L four-cylinder or 2.8L V-6 Jeep engines.
Relatively short length, deep First gear, and nice Overdrive make very driveable combo. TV cable must be adjusted correctly to prevent valvebody damage on TH700R4. TV setup is the most critical and often most complex part of swap. The 4L60E eliminates TV setup at cost of expensive electronic control units, so pick your poison.