Using an external air compressor on an old Loadstar 1700.

What might cause it?

 

Brakes not adjusted properly, bad spring brake.
How about a little context?

 

A good friend was recently killed when his truck rolled back. He had 35 years of no accidents or serious violations. I can’t help but wonder what happened. No way he didn’t set the brakes.

 

If the spring brakes were set for park the only things that would allow truck to move are
broken springs in chambers and that would mean more than one.
Chambers caged.
Slacks badly out of adjustment.
Or if spring brakes are only on one axle on a tandem and that axle is not firmly on solid ground.

 

It didn’t roll right away, it was enough time for him to get under there. I just can’t figure it out.