Dana 20

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.
 Casting #’s on the Dana 20 can differ; however, most seem to start with C18-15. This commonly leads to misidentification of the transfer case as the number was commonly used on the large hole Dana 18 as well. 

Shifter Assembly
The Dana 20 transfer case shifters varied extensively on several models and normally feature a single stick operation consisting of two basic modes, High-Low and 2wd-4wd. The variation of shifters seemed to be based around the multitude of different Jeep models equipped with the Dana 20. The differences were at their greatest when comparing small wheel based to long wheel based vehicles. The shifters were always supported off the front of the transfer case. We have seen on some conversions using large truck transmissions like the Nv4500 where modifications to shifter linkage are required. Our Instruction sheets provide further details for these infrequent alterations.  Many Dana 20 t-cases have been, and continue to be converted to twin stick configurations. An interlock detent pin between the two shifter rails can be removed in combination with a twin stick to obtain better shifting options including independent front or rear low only.

The low range for the Dana was acceptable but not envious with a 2.03:1 low range; however, there are aftermarket low range kits available for most versions of the Dana 20. The front and rear yokes were 10 spline much like the Dana 18. Later years of the Dana 20 would introduce a 26 spline. Advance Adapters manufactures both 1310 Non-CV and 1310CV yokes available in 10 or 26 spline for the Dana 20. It should be noted that the increased number of splines from 10 to 26 were more likely for reasons of increased manufacturing productivity than strength improvement as the increase is actual diameter was minimal. We have however seen failure of the Dana 20 rear outputs shafts under extreme applications. Advance Adapters offer a 32 spline rear output shaft as an upgrade kit under part #50-3020.
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.