A friend of my drives a ´99 Ford F250 7.3psd and has got problems with his powersteering and brakes. The powersteering doesn´t work, when he turns the steeringwheel he almost directly hears a sissing noise (the same noise you hear when you turn the steeringwheel as far as it goes). But if he presses the breakpedal when he is steering you don´t hear the noise. When he brakes it is harder to turn the steeringwheel.

The powersteeringpump has already been replaced.

Does somebody know what the problem is?

Does somebody has got an exploded view of the system?

(My spelling isn´t perfect , I live in the Netherlands...a country where nobody has knowledge about a F250... )