What does a solenoid do?

[1of1547]

I recently got my Turbo 400 rebuilt in my truck. I was having trouble with it shifting. When the tranny was cold it would shift all three gears quickly. As it got warmer it would take longer to shift into all of the gears. On our way home it would not shift into drive. I took it back the the shop and they replaced a solenoid. They said that should take care of my problems after the solenoid breaks in. Does a solenoid need broken in? What does a solenoid do?
It will shift into drive anywhere between 35-45mph. Before I had it rebuilt it would shift at 35 mph. Something just doesn't seem right. I don't like to wind the old diesel up that tight to get it to shift into drive. I don't feel like blowing up my injection pump.

[CHRIS718]

the only thing the solenoid does in a th 400 is force a kickdown at wide open throttle thru the seling off of detent oil and its effect on the lands of the shift valves to control the backshift.this has nothing to do with the shift timing at all .there is no such thing as a break in period for the solenoid,and if the 1/2 shift is on time there either is a problem with the direct clutch pack or you need to add more weight to the secondary side of the governor to generate earlier upshifts. :joint: :arco: :thrashi: :arco:

[1of1547]

Thanks Chris, I am taking it back again because it isn't shifting into drive again.