power steering unit & belt alignment

1995 windstar 3.8lL problem my serptine belt keeps coming off, right now the only thing I see is the pulley on power steering unit has no up & down movement , but the shaft its on does move in & out about 1/8 of a inch do you think this might be my problem, now when the engine is running this pulley does seem to move back & forth, unit is not leaking there is a slight noise in it and steering works good, any help keeping the serptine belt on will be a life saver, I have put this belt on drove 20 miles and it worked great came home parked it let it sit for an hour or two go to crank it up and the belt jumps off, this has happened twice

Thank you Randy Dills

The most likely cause, if the belt is the correct belt and is in good condition, would be the tensioner.....located at the back of the engine compartment.

The other thing that you could do is verify that all the pulleys spin with the belt off.
Make sure tha the belt is routed correctly......smooth surface pulleys get the smooth side of belt and grooved surface pulleys get the grooved side of the belt.

There should not be any significant wobble play in the power steering pulley......if there is, then there is wear in the bearings of the pump.....providing that the pulley is correctly installed on the power steering pump.
The power steering pully MUST be removed and installed with a power steering pulley tool ONLY, pulling or pounding on the pulley to remove or install it is sure to damage the bearings in the power steering pump.
The tool applies force between the pulley and shaft ONLY.....causing no force application to the pump.
You can buy the tool at many auto part stores.

Thank you Sir