I have a 79 F150 4x4 that is doing some strange things. Most of the time it steers ok to the right, a lot of the time it steers hard(no power)to the left, and there is a lot of air in the returning fluid. It occasionally spews over the top after the engine is shut off(I checked the fluid level). There are no visible leaks in the system. The pump was replaced about a year ago, the steering box swapped out for a salvage yard special before that. Is there a particular orientation for the plunger that goes in the pump ahead of the pressure line( direction the holes point)? This problem has been recurrent for as long as I have owned this truck. Any insight would be appreciated!

 

If you replaced the PS pump with a new one and that did not solve the problem then look at the lines for possible holes.I had a PS hose develope pinhole leaks that shot out very fine streams of PS fluid all over under the hood.If you are still getting air into the system possibly the return line is pulling air into the system although I doubt it as usually even a bad return line will leak oil instead of sucking air in.Which brings us to the PS box which may have a bad seal,a crack in the housing,loose bolts, a loose hose connection or is completely worn out.As for your question about the plunger(I take it you are talking about the dipstick for the power steering pump)as far as I know the big cap plastic resivoir pumps can only go on two ways and neither of those has any affect on the operation of the pump.If you for some reason have the older style pump with the steel resivoir and small hole for the dipstick then it does not matter how it goes into the hole and does not affect the operation of the pump either.Hope this helps.
"bowties in the rearview mirror"