Power Steering "grinding" that can be made to go away...temporarily. 97 Tacoma

Maintenance/Repairs
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1 
 Whenever I start my 97 Toyota Tacoma after its been sitting for awhile (generally over night), the power steering pump makes an awful grinding noise. You can hear it even without turning the wheel, though turning it makes it even louder. When the wheel is fully cranked to either side the noise will go away while the wheel is maxed, but return when released. I have found that by holding the wheel in the "maxed out" position (to either side) for a period of time [around 1 minute on average], solves the problem, and the sound will completely go away. Also when the sound is gone, the vehicle steering feels normal.

If the vehicle is then driven a good bit, the problem will not return until the truck sits again for at least 4 hours or so.

A few notes. The power steering fluid level is good, though when "solving" (term used extremely loosely) the problem by maxing the wheel I can see little bubbles coming up, with the pumps cap off. Again, the fluid level is not diminishing, and I have not noticed any fluids where I park.

Also on a few random occasions when the trucks been sitting for an extended period of time, I have turned it over expecting the problem, only to find that its just fine and there is no noise. This is always a little surprising, and a rare occasion. The only thing that I have noted in these rare situations is that it has always been a hot day, though I do not have enough evidence to be completely conclusive in that regard.

My extremely amateur (clueless) theory goes something along the lines of:
       I have some large air pockets in the system that somehow create the grinding noise, and when I max the wheel                      out it puts the pump into overdrive, breaking the big air pockets up into a bunch of little ones. At which point the    system stops making noise and can operate normally. Then the vehicle sits and the little bubbles form back into big   ones, returning me to the state that causes the problem...

Today I got my oil changed, and made sure to ask that they flush the steering fluid, and refill it. While paying, the mechanic noted that my power steering made excessive noise. He was really surprised, when I hopped in, started it (loud grinding right away) cranked the wheel to max for about 15 seconds [takes less time if shes not really cold], and all was normal again.

 I would have all ready bought and replaced the steering pump, if it wasn't for the fact that some of what I have noted above has seemed to really confuse a lot of semi knowledgeable car people. My pops thinks if it was a bad pump, it would just be completely bad, no middle ground. And I don't want to buy a new pump only to find that the problem remains.


Well that was longer than I expected. If you have got through all that and have any input, I will be very grateful and promise to name my 10th born child after you.

-Rex

2

My guess is a small leak somewhere letting air get into the pressure side of the pump. This could be in a hose, pump casing, or steering box. Turning the wheel lock-to-lock is the correct procedure to bleed the steering system. Seeing bubbles rise in the reservoir tipped me off.

Chances are, though, it may be a while before this leak gets bad enough to become very noticable. With a 15 year old truck, I’d consider using this air purge technique until the leak presents itself better and you know what to replace. If the pump, hoses, and steering box are clean, I’d first suspect the shaft seal on the pump. But, I wouldn’t want to replace the pump without being able to verify it is the problem.

Personally, I’ve used power steering stop leak successfully in my wife’s '93 Celica. It was leaking from a spot we couldn’t see because of the impossible-to-reach location of the pump. I used the stop leak, and it stopped within a week and still has not resumed after 2 years.