The Spicer/Dana 18 is a gear driven transfer case that comes in 5
slightly different variations. The early version of the Dana 18 had a
27 tooth drive gear and 3/4" intermediate shaft and 1.98:1 low. The
second generation Dana 18 came with a 26 tooth input gear and 3/4"
intermediate shaft and 2.42:1 low. The third generation Dana 18 came
with a 26 tooth input gear and 1-1/8" intermediate shaft and 2.42:1
low. The fourth generation Dana 18, uses a 26 tooth input gear, 1-1/4"
intermediate shaft, and 2.42:1 low range. The fifth generation Dana 18
uses a 29 tooth input gear, 1-1/4" intermediate shaft, used a larger
input hole, the same case used in the Dana 20, and has a 2.46:1 low
range. The big hole input is about 4" in diameter where as the small
hole input is about 3" in diameter. All Dana 18 cases are cast iron.
The small hole Dana 18s are interchangeable, but the input gear must
match the transfer case. The big hole Dana 18 can be bolted on a
transmission that was originally coupled with a Dana 20 and
visa-versa. All Dana 20 and Dana 18 input gears are 6 spline except
ones used with the 10 spline version of the T-14 transmission. All
Dana 18s and Dana 20s use the 5 bolt "Texas" bolt pattern.
All Dana 18s have front and rear outputs offset to the passenger
side. Trucks built with a Dana 18 have a rear axle that is offset to
the passenger side. Most other transfer cases used in Jeeps have a
centered rear output that couples directly with the input shaft so
that no gears are turning when in high range 2WD. The Dana 18 always
has gears turning which makes it wear faster, noisier, and not quite
as strong as some other Jeep transfer cases. It is still a strong
unit, just not as strong as some other Jeep transfer cases.
A unique feature of the the Dana 18 is the overdrive, developed by
Warn, that attaches in the PTO port in the back. There are also PTO
attachments that can be used to drive winches, generators, welders,
assorted farm implements, and about anything else you can imagine that
might accept PTO input.
The Spicer/Dana 18 was used on the first CJs and their military
counter parts until 1971. It was also used on all other trucks until
around 1965. During the late 60s, many of the larger trucks were built
with the Dana 20. The MBs and GPWs used in WWII used the 27 tooth Dana
18. The CJ-2A up to serial number #24196 in early 1946 used the 26
tooth, 3/4" intermediate shaft Dana 18. CJ-2As after than and the
CJ-3A and CJ-3B (to serial number 54-12506) use the 26 tooth input
gear and 1-1/8" intermediate shaft. The Dana 18 with a 1 1/4"
intermediate shaft and 26 tooth input gear was used on the CJ-3B
(after serial number 54-12506), CJ-5, CJ-5A, CJ-6, and CJ-6A. The big
hole Dana 18 was used with Jeeps equipped with the Dauntless V6
engine. It is not clear if the big hole Dana 18 was ever used with the
134 I4 and T-90 combination, they probably continued to use the small
hole Dana 18 with the T-90. The big hole Dana 18 uses the same cast
iron case that is used on the Dana 20.
Thanks to Fred Coldwell for the first generation Spicer 18 CJ-2A
serial number information. Thanks to Paul Weitlauf for some additional
Dana/Spicer 18 transfer case.
Dana/Spicer 18 transfer case, back view with PTO plate removed.
Dana/Spicer 18 transfer case front view, small hole.
Dana/Spicer 18 transfer case with drum parking brake and PTO cover
Dana/Spicer 18 transfer case with drum parking brake.
Dana/Spicer 18 transfer case.
Dana/Spicer 18 transfer case, rear view. Photo by Daniel Regan.
Dana/Spicer 18 transfer case, small hole case, front view. Photo
by Daniel Regan.