Identification

• The AW4 has a removable bellhousing.
• The case is smaller in diameter than most automatics, and features cast-in ribbing down the rear half of the case.
• The bell housing for the AMC 4.0L I6 engine has a port for the crank position sensor.
• The earlier Jeep AW4 has a 21 spline output shaft for connecting to the transfer case input shaft.
• With the release of the HO 4.0L in the 1991 the AW4 was upgraded to a 23 spline output shaft.
• The AW4 may be identified as model #40-30LE for 4wd versions. and as model #30-43LE for 2wd versions.

Lock-up torque converters

As described above, pumping losses within the torque converter reduce efficiency and generate waste heat. In modern automotive applications, this problem is commonly avoided by use of a lock-up clutch that physically links the pump and turbine, effectively changing the converter into a purely mechanical coupling. The result is no slippage, and virtually no power loss.
The first automotive application of the lock-up principle was Packard's Ultramatic transmission, introduced in 1949, which locked up the converter at cruising speeds, unlocking when the throttle was floored for quick acceleration or as the vehicle slowed down. This feature was also present in some Borg-Warner transmissions produced during the 1950s. It fell out of favor in subsequent years due to its extra complexity and cost. In the late 1970s lock-up clutches started to reappear in response to demands for improved fuel economy, and are now nearly universal in automotive applications.