Here is the history of power steering fluid. This paper has all you will ever want to know about power steering fluids.
http://jimshea.corvettefaq.com/?p=861

I can't speak on the truck fleet. They may have struck upon a combination of ATF and Lucas oil that works for them. I would still recommend genuine GM power steering fluid.

Jim

 

Thanks Jim, I'm going to buy some today. What is your recommendation about a good replacement pump for my car? Since I don't have the original pump anymore I'm thinking about having Lee's build one as close to original specs as possible and using a smaller pulley to get the RPM back close to original. I have a newer model serpentine system on the car and I did the math and it turns the pump about 200 RPM slower than the 75 setup did at idle.

 

If you are going to have Tom Lee build you a power steering pump, make sure that you let him know that your serpentine drive system is turning your pump slower than a production C3 setup. Saginaw made different displacement power steering pumps by making the cam rings thicker and/or more rise in cam ring profiles. You want a higher displacement pump to compensate for the slower rate that your pump is turning.

I would think that Tom Lee will be familiar with pump displacements so as to be able to help you. I am quite sure that he has a machine to flow rate a pump before shipping it to you.

BTW, I continue to read more and more problems with "remanufactured" or rebuilt power steering pumps. I am getting to the point where I would recommend a Saginaw power steering pump out of a salvage yard before purchasing one that was remanufactured.
Jim

 

I'm in the process of compensating for the serpentine system reduction in RPM by replacing the 6.45 inch pulley with a 5.2. The original 75 crank pulley was 7.75 with a 5.75 inch PS pulley (somebody please correct me if I have that wrong) the GM serpentine system is 7.50 and 6.45. The smaller pulley brings the RPM up to just a little more than the original set-up.

Do you know what the pump displacement was for the 75 pump? Which pump could I buy that has the same displacement? If I get the right displacement pump and use the correct flow control valve and pressure fitting would I pretty much have the correct pump for my car? I'm going to the local pick-a-part tomorrow and may just go ahead and get me a good core.

 

I ended up putting a used pump from a 89 Firebird on my car and it works better than the two remans I've installed so far. I used a 5.5 inch pulley to bring the idle RPM up a little. I didn't even take the pressure fitting off. I used the flow control valve and pressure fitting from the 89 Firebird and a high pressure hose from a 1980 model (metric). This was supposed to be just a temp fix until I get the right spec pump but it is working pretty good.