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Best Jeep Transmissions - Lucky 13

Posted in How To: Transmission Drivetrain on December 11, 2007 Comment (0)
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Photographers: Jp Magazine Staff

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.





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.

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.

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.

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.

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.

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.

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.

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.

Forward gearing: 4.01, 2.33, 1.39, 1.0, 0.78
Approximate length: 24.25-inch
Output shaft: 23-spline flush with back of case.
Found in: '00-'04 4.0L Jeep vehicles.
Aftermarket support: Swap bellhousings, adapters, and aftermarket shifters.
Notes: Some bellhousing configurations may place throwout bearing linkage on passenger side, necessitating hydraulic slave cylinder. Liberty models have shifter that points toward rear of vehicle, not straight up like TJ and XJ models, so fabrication may be necessary for shifter location. Up to task of handling moderate V-8 power and tires up to 37 inches.

Forward gearing: 3.34, 1.85, 1.0
Approximate length: 8.12-inch
Output shaft: 6-spline.
Found in: '63-'71 four-cylinder Jeeps.
Aftermarket support: Replacement internal parts, remanufactured units, and engine and bellhousing adapters.
Notes: While standard T-90a gearing of 2.98, 1.66, 1.0 is close, the T-90c's deeper gearing gives the little L- or F-head a fighting chance. The T-90c case will still say T-90a. Shown is very early column-shift version which would definitely be a T-90a. Can pull top cover and count teeth for verification: T-90a has 18 teeth on input gear while T-90c has 16 teeth.

Forward gearing: 5.61, 3.04, 1.67, 1.0, 0.73 ('95-'03 GM & Dodge); 6.34, 3.44, 1.71, 1.0, 0.73 ('93-'94 GM)
Approximate length: 12.34-inch (main case length)
Output shaft: 32-spline (GM) or 23-spline (Dodge).
Found in: '93 through mid-'00s GM and Dodge.
Aftermarket support: Bellhousings, performance shifters, internal replacement parts, and adapters.
Notes: Early GM versions becoming rare and used a 5.125-inch bellhousing index not as widely supported as the Dodge and '96-and-later GM 5.60-inch bellhousing index transmissions. Adapters available for 2WD and 4WD versions of transmission, but 4WD easier to mate to married T-case.

Forward gearing: 4.46, 2.61, 1.72, 1.25, 1.0, 0.84
Approximate length: 24-inch
Output shaft: 23-spline.
Found in: '05-and-later 4.0L, 3.8L Jeep vehicles.
Aftermarket support: Slim to none.
Notes: Overdrive not as good as most five-speeds, but overall tighter gear split from Second to Fifth will keep Jeep six-cylinder in its powerband and will help eliminate flat spots and lugging. Good choice for 4.0L guys, but leave the V-8s to the bigger, stronger transmissions. The crank sensor is in the wrong place for earlier fuel-injected Jeeps, and they have a 270-lb-ft input rating.

We left out a couple of transmissions. For starters, you'll notice there's no Ford C6, C4, or AOD automatics. It's simple-they don't always like to work at angles. When climbing, the pumps can become uncovered and the trannies just suck air while the engine revs and the vehicle goes nowhere. The hot swap for hard-core Ford wheelers is to use a JW Performance Transmissions (321/632-6205, www.racewithjw.com) Ultra Bell to mate a GM TH400 or TH350 in place of their Ford tranny.

Also, while we really like the AW4 auto transmission found in many 4.0L XJ, ZJ, and even WJ vehicles, its relatively complex wiring makes swapping somewhat problematic for the intermediate wheeler. We did stumble across one Web site outlining an AW4 swap into a '99 TJ that was very detailed and should prove helpful to anybody thinking about tackling a similar swap. Check it out in the drivetrain section of www.stu-offroad.com.

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