The Dana 20 is a heavy duty gear driven transfer case that takes a 26 tooth input gear. The case and tail housing are cast iron. The output for the front driveshaft on the Dana 20 is on the passenger side and the rear output is centered. Low range is 2.03 and high is 1.00. The poor low range of this transfer case makes it less desireable.

One way to get around the poor low range of the Dana 20 is swap in Ford Dana 20 and Jeep Dana 18 guts. It is possible, but it takes fabrication and some hard to find parts. There are some great write-ups on-line at http://www.off-road.com/~jweed/transfer.htm and http://www.srv.net/~jrcase/mod20.html

The Dana 20 is generally compatible with the "big hole" Dana 18. The only exception I know to that rule is the version of the Dana 20 used with the Turbo 400 in full size Jeep trucks. This version of the Dana 20 used a different splined input gear. The transmission to transfer case adapter used by the factory for the TH400/Dana 20 is known to be weak anyway.

The Dana 20 can be identified by the center rear output, cast iron tail housing, and deep oil pan. The Dana 18 has an offset rear output, other than that, it looks a lot like a Dana 20. The Dana 300 uses a round bolt pattern with 23 spline input, an aluminum tail housing (often painted or covered with grime), and a nearly flat oil pan. Both the Dana 18 and Dana 20 use the "Texas" bolt pattern with 5 bolts holding on the transfer case.

One variation between the versions of the Dana 20 used in different Jeep models, is the shift linkage. Here's a shot of a Dana 20 out of a '73 Commando. This linkage seems to provide smoother operation.

Usage

The Dana 20 was used in CJs from 1972 until 1979. It was introduced in larger Jeep trucks in the 1963, but it wasn't used in any Jeep trucks after 1979.