I know this one. Maybe Sounds like there is dirt and or sludge in the system. It probably came from your salvage yard rack. Dirty Ford rack & pinion systems are known for that sensation happening.
Start with the cheapest fix first. Get a good shop to flush out your steering system and put in all new high quality fluid. It might do the trick, however, running the pump dry probably caused some wear in there, too.
I once had a '95 Probe GT that began to intermitantly feel like the steering had locked up, usually just turning into a tight freeway off ramp at high speed. The sudden change from power assist to no power is a pretty hair raising feeling, not to mention truly dangerous. A mechanic friend of the family cleaned it all up for me and I had another 60,000 miles of trouble free driving.
__________________ Bone Stock '07 GT 4.6, Redfire w/ parchment leather, Automatic. If it looks right, it is right, and I decide if it looks right. Paraphrasing Sir Sydney Camm (of Hawker aircraft IIRC) |