My son's 68 Mustang, 200 with C4, was running when it lost all gears. No noise, just doesn't move. We had another C4 so my son tried swapping out the pump, no change. Then tried swapping the valve bodies. Still no change, no gears at all. I found out how to test the transmission fluid pressure and bought a 0-300 psi gauge. Absolutely nothing, gauge did not move no matter what gear was selected. From that I would assume that the pump was bad. Is there any other reason why the pump would not pick up any fluid and at least build some pressure?