'64 K20 4x4 Clunk - What is it?

[JimQ]

Hey All,

Relatively new to the forum and classic Chevy trucks.

I picked up a '64 K20 this summer. I've been working on bringing it back to a driver.

We finally got some snow here in S.E. Nebraska and I got a chance to use it drive it in 4wd

When in 4wd, the truck "clunks" and jerks a bit. Maybe once every 5 or 10 seconds. Definitely does it more when accelerating.

I know, not much info here.

I guess what I'm wondering is, could this a transfer case issue? Are these cases known to do this? Or is it more likely a knuckle joint binding?

Any thoughts?

Thanks,

Q