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
desirable.
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. More expensive (but more
available) aftermarket gears can also be used that increase the
reduction of low range.
Aside from the different rear driveshaft offset, 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 and Commandos. 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; stronger aftermarket replacements are available.
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. This linkage seems to provide
smoother operation.
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.
Dana
20 transfer case.
Dana
20 transfer case.
Dana
20 transfer case.
Dana 20 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.
