Re: brakes locked up
If you have air brakes then the maxis are just set and yes, it is a safety feature. But you have a Ford...I fear you have Lucas-Girling brakes. These are hydroboost brakes using power steering pump pressure to provide the power assist. However, they also have a spring-brake safety like air brakes. The power steering pump must provide pressure through a long line to the back where the pressure acts to overcome the spring pressure and release the brakes. If you have a leak in this large line then the system will not be able to generate the required pressure to overcome the springs and the brakes will never release unless you manually cage them. Basically, the system is working exactly as it is supposed to by preventing you from moving with a major malfunction.
Fix the line and I bet your brakes will work again.