I recently replaced the steering rack, pressure line, and PS pump on my wife's 97 Lesabre:
http://www.automotiveforums.com/vbul....php?t=1077384
All went well in the end, except for the PS pump. I can't seem to get rid of air pockets or something. When I follow the prescribed bleeding procedure (raise front end, turn wheel from stop to stop 40 timess, engine off) it gets rid of most air and noise. Then I ran the engine and turned it stop to stop another 40 times. This made the steering very smooth. although I couldn't get rid of the pump whine.
While driving, it works nicely, except the steering and pump slowly get noisier and noisier, especially when doing hard steering while moving slowly, such as for parking.
I then got myself a Mityvac and made an adapter for the steering pump and pumped the reservoir down to 20 in Hg. When I did this with the engine running, the pump suddenly became noisey at about 17 in Hg, then slowly quietened. I though I had it licked so I took it for another test drive. Same thing, fine until I did the hard steering at low speeds. The steering got rough and noisy. When I put the vacuum on again, the pump became noisy at about 15 in Hg, but I got it quiet finally at 20 in Hg.
I left the vacuum on overnight and I just checked it now. Overnight the vacuum held at 20 in Hg. There are no visible fluid leaks.
So far I can only think of two things:
1) there is trapped air somewhere in the system that normal bleeding procedures won't remove.
and/or
2) there is a leak, but downline in the rack somewhere which doesn't show itself until the pump is pulling the fluid from the low pressure line.
Because the vacuum held overnight, I'm guessing that the answer is #1, or something else I haven't thought of yet. Who knows how to bleed these systems?
BTW, the pump is a Fenco rebuild, the rack is Autoline. I would have preferred ACDelco, but neither were available up here in Canada.