Greetings,
Hey, The fan belt on my 1988 F150 351W is jumping on notch off the crank pulley. My only guess is that the replacement waterpump is a little too long, or that the pulley on the PS pump is not on all the way. Both items were replaced about 6 months ago. The PS pulley is not quite flush with the pump shaft, should it be? It looks like it might come too close to the mounting bolts.
Thanks for any tips/suggestions!
I appreciate all the help you guys give!

 

Katt, the power steering pulley should be pressed on as far as possible I think there is a shoulder it hits when its on all the way.Which way is the belt trying to come off?? Front or back of the crank pulley??I think you'll find your problem if you stand from the side of the engine and kind've eyeball the belt and you should be able to see whats wrong.It's probably the water pump,Good Luck Windsor

 

Agree with Windsor,
Using the theory of back-track.
If the belt worked fine before, and became a problem after the two items were replaced, than you know that it has to be one of the two, or both.
Recheck those two pulley alignments.