I broke a Dana 70 rear 35spl. shaft, and twisted the other side 180deg. Then I put in some Dutchman shafts that twisted at the splines, but have not yet broke. That was when the Ford had a 2barrel 390, now Im putting in a 460 and dual t-cases. When the first shaft broke I called Tim at ARB and asked him what my options were, he said 37 spline like some Dodges, or 40 spline. When I break the Dutchman shafts, I will put in another Dana/Spicer set, when they break I will put in a set of 5-ton Rockwells.