2 speed will not shift lo to hi or hi to lo. If I switch the vacuum lines one side works, but the other side does not. Is there a valve between the switch and the actuator. My Thinking is one side of the valve working the other not. Already took the actuator apart and everything looks good including diaphram. I have a 1963 Chevy 2 ton that I still haul grain with. The 292 six engine works great when the 2 speed axle works. NOT SO GOOD WITHOUT. To confirm, The 2 speed will shift if I manually change the hi side to the lo side or vice versus. One line works, the other not. Thanks for any help. IF it is a valve, is one available anywhere?