Power steering mechanical, fluid or air issue?

[Matahoe]

My '05 Tahoe has been experiencing a moderate whine in the power steering over the past year. I have also been experiencing an increase in steering effort and braking as I have the Hydro-booster.

So last year I replaced the p/s pump twice in an attempt to get rid of the whine. That did not work. I then replaced all hoses related to the P/S pump, gear and hydro boost. I still had the whine along with higher steering and brake effort.

Being fed up I decided to replace the p/s fluid in the reservoir and see what that does. So far the results have been much better. It seems that replacing part of the fluid helps for whatever reason. I put new fluid in last year so I am left scratching my head.

So my question is this... Are these symptoms consistent with someone accidentally putting another type of fluid in my p/s system at some point? How about brake fluid Would brake fluid cause whine, stiff steering and a malfunctioning hydro-boost?

 

[CountryBoy19]

According to what I saw over on the truck forums (hydroboost is very common on the trucks, and std on diesels) the hydroboost system is particularly ******* the power steering fluid. One poster mentioned a TSB that stated a 30k mile service interval on fluid for severe service. Many reported a full flush of the hydroboost system cured a number of issues like whining, hard steering/braking etc. Even though my fluid seemed ok, didn't smell burned, and didn't look particularly dark, I decided to flush mine recently for 2 reasons. #1 It has 115k miles on and it may have never been changed. #2 I got a whine and hard steering recently while taking off from a stop-sign.

It took about 3 quarts to get most of the dark fluid flushed out and get to some more clear fluid. I will likely do that more often now seeing as how simple it was. Remove fluid return line off hydroboost, place clear hose on return port and put other end in drain pan (I used a 5-gallon bucket), take cap off reservoir and make sure it's full, start up and push/release brakes while alternately turning wheel 90 degrees right of center and 90 degrees left of center. At the first signs of cavitation (whining) sound in the pump shut engine off and top fluid reservoir off (power steering, not brake fluid). It took me about half an hour but would've gone much quicker if my buddy wasn't trying to talk to me about how many baskets Tom Brady made at his hockey match...

Also, I wonder if they make a funnel with an on/off valve at the neck. I overfilled the reservoir a few times (distracted by aforementioned buddy) and by the time I caught that it was full I still had a pint in the funnel with no way to get it back out...