Front driveshaft diameter

[Short 3/4]

Originally Posted by cbeerman

The GMC 65-66 master parts books shows the front drive shaft as a 2-1/2 tube

That’s very interesting. I’m assuming that is for both 1/2 and 3/4 tons, and with or without locking hubs option? The reason I’m curious is if you do the math on a 4ft long 2-1/2” shaft on a truck with 4.56 gears at 60 mph, the critical speed of that shaft would be too high. Of course with locking hubs that would not be a problem, but otherwise you’d have no choice. I sure wish my 64 K20 had still had its original front shaft installed when I bought it, as it did not originally come with the locking hub option. It was originally a utility service truck, so would have been driven daily both on and off the highway. Of course maybe that’s why the aftermarket hubs pictured in my signature were installed when I got it.

Anyway, thanks for the info. I like that this is a safe space for people like me with such obsessions. I’m amazed at all the vintage tech literature you manage to dig up and share.

Tom