In case anybody doesn't know. The brakes on air brake trucks (which is all of them) have a spring mechanism pushing on the brakes at all times, if the air system loses too much pressure, such as if the operator engages the parking brake, then the air inside the air chamber at each of the brakes wont be able to hold the springs back and the system will fail safe fully engaged. If you need to tow the vehicle you will need to manually unlock the brakes by turning those bolts which compresses the springs and releases pressure on the brakes so the wheels can spin.
That is, they're fail-safe: in their unpressurized state the brakes are set hard. Air pressure lifts the brakes, so any break in the air line stops the truck rather than leaving it flying down the road without brakes. Trains work the same way.
While you are mostly accurate, you would need to know how to cage the brake cans, there is usually a "bolt" (more of a piece of allthread with a t at the top) that you would install in the brake can and then tighten the nut and washer down until the bolt pulls the plate inside against the springs to release them, this needs to be done on the cans on both sides of each drive Axle. The drives are usually the only spring brakes on a rig. Trailers follow suit.
(post is archived)