Power steering fluid overflowing when bleeding brakes?

Hello all,
I was here about a year ago getting alot of great help in my 6.2 to a 6.5 swap in a '85 K30. That project turned out great thanks to all your help. I'm back with a brand new problem... A few months ago I installed a 6" lift, with a crossover steering kit from ORD and a brand new steering box from ORD. When doing this I put on longer brake lines to the wheels and replaced some brake line tubing for the rear brakes. I bled out the system and every thing was working well, until a few days ago. I took the truck out and the brakes were real soft and pumping the brakes would not build pressure, so I turned it around and brought it home. Went out this morning to bleed the brakes and found that with the truck turned off, when pumping the brakes, power steering fluid was coming out of the power steering reservoir cap. Brake fluid level was not dropping noticably. I had checked my power steering fluid before I started this and it was sitting just a touch over the "full cold" mark. Shortly after the engine swap I had the brake system flushed, It's a brand new power steering pump from the engine swap. Maybe 3000 miles on it at this point. Any thoughts on what is causing this would be appreciated.

with the truck running fluid does not come out of the power steering reservoir cap and I can't get any brake pressure, no resistance on the peddle. Turn the truck off and I have pressure, at the brake pedal anyway, and fluid streaming out of the cap. Is there a pressure relief valve in the hydroboost unit that could have failed? With the power steering pump turning and making pressure it is just recirculating back into the reservoir and not able to build pressure at the brakes. Turn off the power steering pump and any pressure I am generating at the brake pedal is forcing the power steering fluid to bypass into the reservoir and fill it up, being as the power steering pump is not moving it through the system. After it sits the power steering fluid level drops back to where I started, just a touch over the "cold full" mark. Does the power steering pump keep an accumulator pressured up that acts on the brake system? I can't visualize how my braking system could be acting on my power steering system in such a manner. Thanks

Also, If I had the two low pressure return lines into the power steering reservoir switched would it make a difference? One from the power steering pump and the one from the hydro boost unit. One diagram I found shows them the opposite of what I have and another diagram shows them joining together in a "t" fitting and dumping into the reservoir at a single point, which leads me to believe it shouldn't make a difference. The return line from the hydro boost unit is the one that I am imagining is the pressure relief and might have a failed valve.

The low pressure line downstream routing doesn't matter. They just dump back to the PS pump reservoir.

Either your lines are incorrectly routed, or the hydroboost unit is shot.

Verify your line routing. PS pump connects to the hydroboost inboard port, and the hydroboost outboard port connects to the steering box. The forward hydroboost port is the return.

once again you are a huge help! I believe my hoses to be correct. "Inboard" being the single port on the inside of the hydro boost, toward the fuel filter, and outboard being on the outside,rear of the hydro boost, toward the firewall. Thanks for your help.

im no expert, and i really dont know right off how the hydro boost works entirely. i do know how the vaccum booster works on a regular car though, and can only imagine it's the same principle, but hydrolically. that being the case i think you nailed it in your second post. i'd assume a valve in your hydroboost failed as it's supposed to work off of residually built up pressure. the only thing that actually allows it to apply the brakes is the pressure created from your foot on the pedal. in vaccum boosters on a car, once done pressing on the pedal, a spring presses the diaphram back out which allows the vaccum to be ever present to help with braking again. with hydro boost, the vaccum is replaced with power steering fluid pressure that is otherwise unused for the most part. by pressing your brakes, the residual pressure from the power steering pump should be helping you apply your brakes. so if pressing your brakes is forcing the power steering fluid out of your pump. a faulty hydro boost seems logical. again, im still learning and no expert. but it seems like a logical direction for your diagnosis. im going to inquire about this to my boss, as it's something i would like to learn about now lol. i'll let you know how that turns out if you're interested.

p.s. lol only after i posted was i able to read the other two posts after your second...

Put in a new hydroboost unit and a new master cylinder while I was at it. Bled out the brakes using one of those hand pump vacuum units. First time I've used one of those, only way to go! Brakes were the best they've ever been. Just got home from work and the truck has been sitting for a month and the brakes are soft again. I'll have to dig into it in the next few days. Thanks for your help and input.

I've never had much luck with the hand units. I always seem to get some air in.

Went to one of these years ago and never looked back:

https://content.speedwaymotors.com/P...66c31d989a.jpg