I destroyed 2, 7 1/4's, with a stock 1977 2 barrel 318 in a "Roadrunner" of the same vintage. The last one was a SureGrip. Did all this carnage on E-70x14 Goodyear Polyglas rim protectors. The first one went snap pulling out of a gas station and turning right. The second one went snap when I found myself going backwards at 60MPH, after hitting a foot of water in the road that I didn't see in the dark, and I floored it. On the other hand, I've seen 7 1/4's live forever with the right gears. The break seems to be around 3.55. I have a 3.55 in my '66 Valiant that is showing no signs of distress, and Dad pulled a 25' travel trailer using a slant powered '67 Valiant with 3.91's for years. I'm guessing the smaller pinion gear on the lower numerical ratios puts too much side load on the carrier and they split. If you want your 7 1/4" to live, lose the highway gears. Just my $.02.