Technic 1977

[N. W. Perry]

Known errors: slight (2 LDU on each side) collision, between the vertical beam, bottom pins and top axles

Ah, yes…you have to scale down the tower of 2x2 bricks a little bit in order for it to fit properly. (You can either spread the 2 LDU across all seven bricks equally, or as I did, just make two of them 1 LDU shorter and hide them in the middle somewhere.) 

Also, you'll find that in real life, the fork assembly isn't perfectly perpendicular, but sits at a slight angle inside its mechanism. And of course the whole thing does tend to bind up a bit; it's just one of those cases where the real-world model depends on some amount of physical flexibility that LDraw simply doesn't represent. That was common in early Technic, after all!