I just did a power steering pump replacement and had a hell of a time getting hydro boost to work, until I bled and flushed the hydro boost. When I did that I got a whole bunch of nasty looking oil out of the whole system [likely why the Power Steering pump failed and why the hydro boost wasn't really working right to start with].
What you need:
Some clear tubing [use once, discard it, it's cheap] to go from the RETURN line out of the hydro boost to....
A bucket [item 2]
3. 4 qts. of either power steering fluid, or Ford approved Mercon trans fluid.
4. A helper.
5 Jack and jack stands.
Remove the return line at the hydroboost, lay it to the side or tie wrap it out of the way, install the clear hose at the hydro boost and put the other end in the bucket [I used a 2 qt clear plastic bucket from the paint department at ACE hardware], cheap, disposable.
Jack the truck just high enough to get front tires off the ground, secure on jack stands [be safe please]
With the power steering pump at the full mark, have your assistant start the truck and slowly cycle the steering wheel full stop left then right [or right then left] while slowly pumping the brake peddle. Watch both the fluid level in the power steering reservoir and the bucket. As long as the assistant is turning the wheel and/ or pumping the brake you will get fluid through the Hydro Boost and out the return line into the bucket. You will see the dirty oil coming out the clear line.
DO NOT let the reservoir get low. When it does stop your assistant from moving slowly cycling the wheel and pumping the brake, and add more fluid. Keep doing this until the fluid that comes out is as clear as the fluid going in [Ok , it's not a perfect world.. get it close as you can.]
After I did this, my Hydro boost started working like a new one, really amazing how much better the brakes worked, whining of power steering pump cleared up and I now know I have clean oil in the system.
In my opinion.. this needs to be a regular service item with hydro boost systems. I'm sure mine had never been done in the 200,000 plus miles by previous owner... the oil out was vile nasty..
Reconnect the return line, top off the reservoir, and you should be good.. [might want to take out the jack stands before test drive ]
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