Maybe someone with more knowledge than me can shed some light on this subject. Were having issues with the PTO staying engaged, so we proceeded to take the valve off to inspect. Please see the attached mocked up picture of what we've encountered...I suspect the 1/4 ball that lives in the machined bore acts like a detent. But how does it work? On the valve we took off the working tractor, there is a piston with a 1/4 ball underneath it, no spring in this assembly... On the valve we took off the parts tractor, there is a spring with a 1/4 ball underneath it, no piston! I assume the spring keeps pressure on the ball, when the valve moves, the ball falls into a groove keeping the PTO engaged...We don't have a spring in the valve assembly we took off on the working tractor....Is this our problem, why the PTO won't stay engaged?