7 1/4 why weak?

I broke 3 7 1/4 axles in 4 years in my old 68 Barracuda with a 318 with 9.2 compression, stock 340 cam, 600 vac secondary and dual exhaust.

Basically a 318 with a 340 cam and 4 bbl and dual exhaust. It can't handle much over a stock 318.

that's why they are weak.

After I went to an 8 3/4" axle, I never broke another one again for over 200 k miles on that same car....