Yep, I blew up three 7 1/4" axles within 4 years in my 68 Barracuda daily driver with just a mild 318 with a 340 cam, 360 heads, stock square bore 340 intake, holley 600 vac secondaries and dual exhaust.
Basically a 318 built to a 340 specs....
The third and last time, the driver's side axle came out on the highway with the tire still bolted to it and passed me on the shoulder at 55 MPH...
I then went to an 8 3/4 sure grip and never had another axle problem, and drove the Barracuda to 500,000 miles before the body got too bad to keep going...
