We are often asked our opinions about the strength of the Dana 20. The reader should be aware that these were the transfer cases that were found in the Jeep J4000 one-ton truck, where they perform most admirably. A Model 20 that breaks is usually due to a worn intermediate shaft and bearings, other worn bearings, or from the shock force resulting from an unskilled driver panicking his way through a rock patch. We've yet to see a broken Dana 20 transfer case in our own service, and we find them to be a most outstanding gearbox.
It is nearly remarkable how much power this compact transfer case can transmit and sustain. It is not so rare to see them handling Big Block grade power and deep, compound gearing.
The 10 spline vs. 26 spline shafts show no greater nor less tendency towards breakage, as the shaft diameters (the real measure of strength, not spline count) are very similar. The gearset in the Dana 20 is strong, but unbalanced. The front seat is helical and the rear set is spur cut. When in low range and under extreme torque, the helical gears produce significant side loads against the case. Though breakage is not at all common due to this, it is possible.
We've discussed the Dana 20 case casting with individuals and a couple have mentioned that Dana cast three or four different thicknesses depending on whether they were slated for an HD J Truck, other FSJ, Commando or CJ. We've not seen evidence of this, but will keep our eyes and ears open.
Ford Bronco Model 20
A similar version of the Dana 20 was made for the Ford Bronco. It featured a 2.46:1 Low gear and a driver's side front output shaft. The internals are largely the same as for the Jeep, IH and Chevy versions, but the front mounting pattern is quite different and not compatible with the other popular Dana 20 adapters and transmissions. Of note, it is possible to swap a Bronco sliding gear into the Jeep or IH Dana 20's - along with Model 18 gears - to acheive a 2.46:1 Low.
