Doesn't that truck have Huck brakes, with the two hex heads on the back and top of the backing plate? There are some springs under the heads. Do not force if they don't turn easy. They are easy to brake the small disc inside that turns the adjusters on the wheel cylinder.

A day without laughter is a day wasted- Charlie Chaplin
When wrestling a grizzly bear, you have to keep at it until the bear gets tired, not when you get tired.
1948 Chevy 2-Ton