Dana 20 Transfer Case
The Dana 20 was the end product of some rather simple yet innovative design changes to the Dana 18. The result was a durable and dependable transfer case capable of handling the heavier vehicles and more powerful engines Jeep was introducing.
Although the Dana 20 can be considered as the transfer case that replaced the Dana 18, the design and implementation of the Dana 20 evolved over a decade before this transfer case would actually replace the Dana 18. The Dana 20 was first released in early 1963. It was marketed as the “silent transfer case”. This was obviously in reference to the noise issues some were having with their Dana 18s. The "silent" version was accomplished by the new centered rear output housing. This greatly diminished wear while in 2wd. The output shaft housing was centered or in line with transmission basically bolting to the same area previously used on the Dana 18 as the PTO port. The rear output low range gear slid over the clutch teeth on the high range speed gear which was directly affixed to the transmission output shaft.
The early applications were typically Jeep j-trucks and wagons. These vehicles used the TH400 as the factory transmission. Jeep used an oddly engineered adapter to mate the TH400 to the Dana 20. Jeep apparently acquired 2wd TH400 output shafts from Cadillac with a large robust 32 spline output shaft; however, the actual adapter that mated the transmission and the transfer case was a flimsy cast adapter which was heavily prone to failure. Advance Adapters offers a replacement adapter kit to correct this faulty design under Kit #50-0500.
The Dana 20 would eventually find its way into the CJ models as well, with complete replacement of the Dana 18 by 1972. Unlike the TH400 version of the Dana 20, the manual transmission applications remained with the typical 6 spline output shaft as used on the Dana 18. These transmissions would include T14a, T-15, T18, & T-150. As mentioned previously the TH400 was the only automatic Jeep would use behind the Dana 20. It should also be noted that International Harvester also utilized the Dana 20 in some of their smaller 4wd vehicles. The manual transmissions used by I.H. were the T18/T19 and their Dana 20 transfer cases were identical as with Jeep transfer cases including the 6 spline output shafts. I.H. also used the Torque Flight Automatic with the Dana 20, This Dana 20 was unique as the output shaft of the transmission was actually 23 spline.
Identification and features
The Dana 20 remained a cast iron transfer case like the Dana 18 and also retained the passenger-side front output. Although compact in size at only 10½” and relatively light in weight, the transfer case was quite dependable. The 5 bolt pattern on the front of the Dana 20 was carried over from the Dana 18 and can best be described as the state of Texas. The front indexing hole was 4”, the same basic design used with “Large Hole” Dana 18 transfer cases. Since the Dana 18 and Dana 20 share the same common bolt patterns and spline counts, Most of the adapters manufactured by Advance Adapters are for use with either transfer case. Likewise the large Dana 18 indexing retainers will also need to be used on the Dana 20 as with the Dana 18. These retainers were not commonly used on factory Dana 20 applications but will be required.
It is fair to say, the Dana 20 made its mark on the history pages of Jeep. The transfer case was strong and dependable, but its compact size did limit its use. By 1979 the Dana 20 was scheduled to be replaced. Many had apprehensions as to any transfer case capable of replacing the vulnerable Dana 20. Surely no t-case could match to the brawn of the Dana 20. Could it? The Dana 300 was the next transfer case to be used and what a case it would turn out to be.