AMC and Jeep transmissions


Vehicles made by American Motors Corporation and Jeep incorporated a variety of transmissions and transfer case systems. This article covers transmissions used in the following vehicle models and years:
used in later AMC vehicles came with either a 21-spline or a 23-spline output shaft. Transmissions coupled to four-cylinder engines typically used 21-spline output shafts. The 23-spline manual transmission was universal in the Eagle lines and was generally used with six-cylinder applications. All transfer cases were available with inputs matching either 21- or 23-spline shafts, making transmission swaps possible among various models and years. However, the depth of transfercase input and length of trans output changed, and there is 15/16" difference between early and late models.

Manual

The following manual transmissions have been used in the vehicles listed above:
The following automatic transmissions have been used in the vehicles listed above:
The Aisin-Warner four-speed automatic transmission was co-designed by AMC and Borg Warner, and built by Aisin in their new facility for use with the Cherokee XJ's 4.0L inline six cylinder engine. It was manufactured by Aisin-Warner, a member of the Toyota group, in partnership with Borg-Warner. It shares many parts with the Aisin 450-43LE that is used in Toyota off-road vehicles.
The AW4 is also used behind the 2.5 L AMC Straight-4 engine. It has a removable bell housing with a mount for the crankshaft position sensor. Early AW4s used 21-spline output shafts. In 1991 the AW4 was changed to a 23-spline output shaft, concurrent with adoption of the High Output inline six-cylinder engine. Some sources state that the output shaft spline change occurred for the 1990 model year. The change most likely occurred during the 1990 model run with early 1990 models receiving 21-spline transmission and later models receiving 23-spline. If swapping transmissions in 1990 model year vehicles either swap the transfer case as well or make sure to check spline count. The input on the transfer case can also be changed to match the output shaft spline count. Rear-wheel-drive-only transmissions all have the same spline count on the output shaft, only 4x4 models are affected by differing spline count.
Gear Ratios for the AW4:
Models that used the AW4:
For the 1972 model year, AMC began to purchase a variation of the Chrysler-developed TorqueFlite transmission and named it TorqueCommand. All TorqueCommand automatics used 23-spline output shafts. Later on, as AMC revised their mainstay engines to have lighter casting technology, these transmissions were available in both the Chevrolet small V6 engine pattern and the AMC late model pattern that was used on their I6 and V8 engines. Other than the bell housing pattern and the torque converter, the AMC version is the same as other Chrysler transmissions—all parts interchange engines. The 2.5 L kept the same pattern through the end of production. For 1979 through 1981, there was also an Audi 2.0 L pattern 904.

Transfer cases

The transfer case is an :wikt:auxiliary|auxiliary transmission that connects the front and rear axles. It also commonly provides a selectable secondary gear reduction. AMC and Jeep vehicles have used several different transfer cases in their various models.
Summary of AMC/Jeep Transfer Cases

See below for further information on New Process/New Venture transfer cases.

Dana

Jeep has used three different transfer cases made by the Spicer Division of Dana Holding Corporation. They are the 18, 20, and 300 models.

Dana 18

The Dana 18 is a gear driven part-time transfer case. Both the front and rear output shafts are offset towards the passenger side of the vehicle. Drive modes offered include 2-wheel high, part-time 4-wheel high, and part-time 4-wheel Low. All Dana 18 cases are cast iron and use the "Texas" bolt pattern with five bolts holding on the transfer case. There are five variations:
The normal input Dana 18s are interchangeable, but the input gear must match the transfer case. The "big hole" Dana 18 is transmission-interchangeable with the Dana 20. Almost all Dana 18 and Dana 20 input gears are 6-spline; the only exception is the one used with the 10-spline version of the T14 transmission. Some International Scout Dana 20s with a 727 automatic transmission use a 23 spline 26 tooth gear
All Dana 18s have front and rear outputs offset to the right side. Most vehicles built with a Dana 18 have the rear axle offset to the right side to accommodate this. Most other transfer cases used in Jeeps have a centered rear output that lines up with the input shaft. The Dana 18 always has gears turning, which makes it noisier then some other transfer cases when in two-wheel-drive mode.
Applications:
The Dana 20 can be identified by the center rear output, cast iron construction, and deep oil pan. Like the Dana 18, it uses the Texas bolt pattern to hold the transfer case in place. This is a heavy-duty, gear-driven part-time transfer case with a 26-tooth input gear. The output for the front drive shaft is on the right side and the rear output is in line with the input. This enables 2-wheel High to be direct-drive, which is quieter. Otherwise the Dana 20 offers the same drive modes as the Dana 18. Its low range has a ratio of 2.03:1.
The Dana 20 is generally compatible with the "big hole" Dana 18. One exception is the version used with the THM400 in full-size Jeep trucks, which used a different spline number on the input gear.
Applications:
The Dana 21 part-time gear system with single-speed case with automatic transmission. The Dana 21 is essentially a Dana 20 without a low range.
Applications:
The Dana 300 part-time gear-driven transfer case. That uses a round bolt pattern and has a nearly flat oil pan. It is a heavy-duty, gear-driven transfer case with a 23-spline input shaft. The case is cast iron but the tail housing is aluminum. The ID number C300-15 is stamped on the case. The output for the front drive shaft is on the right side and the rear output in line with the input. Low range is 2.62:1.
One common modification of the Dana 300 is to add oil paddles to the main shaft to prevent oil starvation of the rear bearing.
The Dana 300 was used in Jeep CJs from 1980 to 1986. The 1980 factory original came with a shorter tail housing and a longer rear drive shaft. The Dana 300 should fit behind all TorqueCommand 4x4 transmissions.
Applications:
In general, New Process transfer cases are identified by a three-digit code. The first digit determines the number of gear ranges. The second digit is a series number that reflects design, and provides minimal information about torque handling. For example, if the second digit is a 1, there is no two-wheel-drive option; if it is a 2, 2WD is available. Other numbers have similar meanings. The third digit indicates differential type: 1 means locked, 2 means open, 3 means electric locked, 4 and 5 both indicate an asymmetrical torque split planetary gear and gear drive, 6 means an electronic clutch pack, 7 means a hydraulic clutch pack, and 9 means a viscous coupler.
The AMC Eagle used three New Process transfer cases that were single speed versions of the models that were used in 1980 and newer Jeeps. There was no difference between the Eagle versions and the Jeep versions other than the addition of a low range, indicated by the 2 as the first digit.
New Process transfer cases are chain-driven and use a circular 6 bolt, 23-spline input on the case. The output for the front drive shaft is on the left side. The New Process transfer cases used by AMC attach the same as the Dana 300 except that New Process cases have the front output on the left side. Interchange is possible, but there is an indexing lug in the pattern, in an attempt to allow the transfer case to attach in only one position. Thus, some modification on the transfer case or the adapter is required.
Because of changes in the name of the manufacturing company, new versions of the NP231 and NP242 are referred to as NV or NVG.
New Process Transfer Cases Used in AMC/Jeep Vehicles

↑ The 249 was available in two versions. The early version had no differential lock and the viscous coupling spanned the center differential, creating a 50/50 torque split. The later version had a viscous front drive, creating a rear torque bias, but included a provision to lock the center differential.

Overdrives and underdrives

Borg-Warner overdrive was available from early 1960 to 1969. The Borg-Warner overdrive case is 11¾ inches long, including the adapter. A complete T96 with overdrive is 18¾ inches long from front of case to end of tailshaft housing. The overdrive unit is the same for all.
The Dana 18 has a power take-off attachment on the case that can be used to drive equipment that accepts PTO input. A unique feature of the Dana 18 is the overdrive that attaches in the PTO port in the back of the system. An adapter allows use of both the overdrive and the PTO attachment, but it is no longer produced.
Laycock de Normanville overdrive was available from 1974 through 1976 for inline six engines with the 150T and for V8 torque tube cars with the T89.

Transmission to transfer case adapters and clocking

Transmissions end with a splined tail shaft, more commonly called an output shaft. When one or more auxiliary units are bolted to the main transmission, these are called adapters, extension housings, or tail housings. All factory applications with a four-wheel drive transfer case require an adapter, and many upgrade transmissions that would otherwise be incompatible can be adapted to Jeep transfer cases.
Clocking refers to the angle at which the transfer case is tilted with reference to the horizontal plane. Stock Jeep clocking for the Dana 300 is usually 23° and stock Eagle and Jeep/New Process clocking is usually 13°. Many factors, most notably ground clearance and front drive shaft clearance, can necessitate a change in the clocking angle. Some aftermarket adapters feature flanges with multiple clocking options.

Bell housings

The bell housing bolt pattern for the old AMC 196 Straight-6 engine is the same as for the more modern early 199 and 232, but the 196 had different dowel pin sizes. AMC's 1956 to 1966 V8s used a different bell housing bolt pattern that was slightly larger in diameter than the six cylinder bell. When AMC discontinued their first V8 engine design after 1966, the bell housing changed; all 1966-up V8 bell housing bolt patterns are the same. The bell housing for six-cylinder engines changed to match the V8 in 1972 when AMC switched from Borg-Warner to Chrysler transmissions automatic. The flywheel also changed from 153 teeth to 164 teeth. Starter motors used with the 1966-up V8 bellhousing were sourced from Motorcraft which interchanges with the Ford V8 and some of their inline sixes - the Jeep 4.0 L uses a Mitsubishi-designed starter which has an integrated solenoid which is lighter in weight but retaining the two mounting bolts with a threaded top hole and unthreaded hole which bolts to the transmission bellhousing.
The Iron Duke I4 used by AMC in Jeeps from 1980 to 1983 used the standard small block Chevrolet bolt pattern bell housing. The later AMC I4 had the GM 60 degree V6/I4 bolt pattern, and this was retained for the life of the engine. AMC often used lighter duty transmissions with the four cylinder engines.

Applications