With the exception of the ’70½-’75 CJs and Jeepsters, all CJ, Willys pickups, Wagons, Jeepsters, and pre-’70 FSJs had weak two-piece rear shafts. A nut held a tapered outer portion of the rear shaft to the drive flange. If the nut loosened, the hub could walk off the shaft and sheer its Woodruff key, ending your outing. Early Dana 41 and ’49-’60 Dana 44 rear axles used 10-spline shafts while the late ’60-early ’70 Danas had 19-spline shafts. The 1970½-1975s got one-piece 30-spline shafts. You can’t put the one-piece shafts in the two-piece Dana 44 rears, but you can buy full-float conversion kits to change your 10- or 19-spline semi-float Dana 44 rear to full-float 30-spline from ATV Manufacturing. Don’t forget you’ll need to change the diff carrier. If you have a ’76-’85 CJ, you can upgrade your Model 20 two-piece shafts to one-piece with conversion shafts from a variety of manufacturers.