Hydro-boost question
 

So, I am a fan of changing out parts before they fail. No fun having a broken truck on the side of the hwy with angry wife. :rolleyes:

I changed out the Steering box to a Red Head, expensive, and I am told the new GM boxes are junk unless its the one that came with the truck, and factory power steering pump. Still, I get the hard to steer at a complete stop unless I start rollling the truck forward or back, then its easy or like it should. It did it only turning left before I changed out everything, including all related hoses. When I brake, the ower steering pump started to hum like the pump is running dry only to discovered its complete full. All fluid had been changed out but after 5000 miles, its started to get light brown again. All this done at a reputable shop.

Today, I had my kid help bleed the hydroboost system again to see if it make any difference. Few bubbles came out. Breaks feels so much better and stop so much faster. When he hit the brakes, a bunch of bubbles came out of the power steering pump reservoir. Here's the kicker. The steering is really hard to turn now standing still (turning both sides now, not just left) until I roll slightly then it frees up. Any thoughts? Its an 2006 Duramax crew cab, long bed, 4 wd if that's important.

I read GM knew about the issue. They have a fix with some electronic switch but my year isn't affected.

How does it tie into the brake system?

My take not knowing more information.: The pump supplies pressure and volume of fluid to the booster and steering box. It's a 'closed' hydraulic system that will bleed off any air pockets or bubbles in operation. The pump is always working when the engine is running and has a high pressure relief valve. It is a very simple design - so it either works or does not assuming you're using the correct fluid.

With the hydro-boost the assist portion for brake apply is a little more complicated but again with fluid pressure and flow it either has assist or a rock hard brake pedal.

The steering box has a recirculating- ball valving system that reacts to steering input shaft rotation. The pump is always moving fluid through the system with the engine running. If I understand your post, the assist part of your brake system is working normally. The box is not, is that correct?

I have no idea if the guy below knows what he is talking about but it's in the ballpark of your issue. I am sure you turned your steering wheel with and without the brakes applied when not moving. Also, I think I read you replaced your power steering pump. No leaks, right?

a shiet hydroboost full of gunk would not flow as well, and would cause a restriction which would allow more pressure to flow to the gear box, the new unit is nice and clean inside so the weak pump cant keep up with the flow of both. i would put a new pump on, there like 100 bucks from the dealer (do not buy a reman) and make sure you KEEP YOUR FACTORY PULLEY

also, IIRC the new pumps have a higher pressure regulator to address the known issue with poor turning while braking. so win win either way. install of just the pump is easy, just a few bolts and a couple 1 hard line 1 or 2 return line(s). when you get the new one, do not put fluid with stop leak in, it swells the seals for no reason.

https://www.duramaxforum.com/threads/power-steering-pump-sudden-hard-turning.739018/

Turning steering wheel with brakes pressed, not moving. Shall I try it on P or N? All lines, pulley, pump (factory GM), and Steering box but I did not replace the hydroboost behind the brake reservoir. No leaks anywhere. Maybe I should ditch the old fluid and just use GM or AC delco? I think it NAPA or Valvoline in there now?

Interesting.......seems the guys at the duramax forum have experienced this.

Sure, just try it in park/ neutral without brakes depressed.

You have replaced the lines which surely came with new o-rings. Saying this because I have an Odyssey that had a leaking line o-ring on the suction side of the PS pump. It never leaked and I don't know why (high up on the engine?) . However, it sucked air badly when running. Constant noise maker and foamy fluid in the reservoir.

I don't understand enough about the hydroboost system to state why there were bubbles appearing in the PS reservoir when you hit the brakes. That's an odd one.

I have replaced a hydroboost unit on an Escalade. It was a moderately cumbersome job but it may have no comparability to your set up.

I would get your google on to see if there is a preferred fluid and change that out first since the existing is changing colors.

I been on the computer on and off for the past few months. I have more questions every time I read something. I don't really understand how it really work as to how it ties into the brake system and yet the brakes has its own fluid. I see the pipe going into the brake booster if we can call it that back behind the reservoir. I jsut took it on a 30 miles drive running errands. Stiff even without being on the brakes. Hits a hard spot right around 1/2 turn of the steering wheel on both directions. Does it in N or P, doesn't matter but as soon as I starting rolling, it all goes away. When its gets hard, it feels like no power steering, I can hear the pump starts to hum, the typical sound if the steering wheel is held at full cranked.

I tell ya, my brakes works like if its the 930 now. I did not bleed the brakes at all but crank the wheel without the engine running back and forth about 8-10 times with front wheels off the ground. I am going to try and flush the system and run AC celco fluid ans see if it helps. If anyone want to educate this dummy, please don't be shy.

The pump supplies the hydraulic pressure to operate the power assist for the brakes that is in series to then the steering box. So it's possible there may be blockage after the booster as the fluid exits. Best thing to do is put together a "tee" in the pressure line to the box. Then you'll need a gauge that goes to @ 1200 psi in the tee. That way you'll be able to see what the line pressure is to the box. It's the only way to know for sure to identify what's going on.

Fluid exiting the hydro boost is low pressure iirc.

Been a while since I hooked it up in the Triumph. I remember my biggest issue there was cavitation - which I fixed by filling the reservoir from the bottom rather than the top

The other issue was flow. I had to get a better GM power steering pump to get enough flow to get both working. OP - Are you sure that’s not the issue?

Alan, I am not sure? I am trying to understand how it all works, forget working on it. I will try. Now my interest is pegged about the pressure? I wonder if they got me a new old stock pump from GM instead of a newly revised one?

It’s pretty simple if you understand brakes.
The hydro boost replaces the servo.

I was looking for a picture but post 2 is likely your issue.
https://www.classicwinnebagos.com/forum/index.php?topic=9126.50

Updated pump (Higher flow) will probably fix it.

The assist part is working only if the truck is moving ever so slightly. I can only turn the steering wheel half way and it feels like no assist at all. The brakes are working but until I bleed the fluids yesterday, it worked great. It would make noise at time when I depress the brake pedals, similar to an low fluid power steering pump noise but comes and goes.

I am thinking now I need a power steering cooler. There's not one in the truck.

That's a lot of info. Much to learn and understand. After reading, I really don't think its the steering box.


Is there a test performed to find out if the pump is the real issue? I need to take this to someone else. These guys know Duramax engines, not I am questioning their knowledge on brake systems. Thanks for the tip. Off the read more.

I don't believe so as the box needs pressure and flow to operate and is after the booster. There should be a spec for line pressure.

Also I would not change anything or add anything to the mix as the problem hasn't been identified yet.

Went back and looked at the setup I have.
Two lines out of the hydro boost. HP to box, LP to reservoir.

I remember the LP because that was my first - and worst - issue. Filling the reservoir from the top allowed the fluid to get air bubbles. After a run it would cavitate and squeal like crazy.

Swapping the reservoir to return to the bottom fixed that.
After that it was a higher flow pump to do the rest.

For full disclosure though mine was a custom setup.
Custom Appleton rack, type2 pump and mustang cobra hydroboost. All GM may not need more flow.

So is it fixed?

Common on the hmmwv's to blow a line and kill the PS pump.

No, hadn't had time to look or take it in but will report back once I find out. I am at a lost still but start to understand how it works after some reading

I guess that it's already been explained that the PS pump supplies the assist to both the steering and the hydroboost brakes. It's very important to use the right oil in it and bleed it completely, other than that, it's a pretty simple system.

You say that you like to change out parts before they fail; I hope this doesn't mean that you are changing out perfectly good, functioning factory parts for replacement parts just to create problems in your life and forum threads(?) The parts that came on that truck are ALWAYS going to be better than anything you can buy 14 years of globalization later.

Was the steering box bad that you replaced? I have a Redhead box, (that sounds dirty), sitting in the box waiting to be installed on my 230k mile 1999 Ford F-250 but the original box is junk from someone over tightening the adjuster before I got it. Same w the PS pump, was it failing?

DanJ, a poster here has a 2006 Duramax dually that he bought new w 300k? miles on it that he's never done anything to other than brake pads and fluid changes. Says it's the best piece of machinery he's ever owned, period. And he is way more than qualified to replace parts on it if needed.

At this point, start w draining and refilling it w the correct, GM fluid. I've never understood people who spend all kinds of $$ and time changing parts and then get cute w the lubricants...trying different products off the Autozone shelf. Use the right oil, period and have an easier life. That's my experience, anyway. I've only owned about 150 vehicles so it's a small sample but still.

I told you from the start that when you bought the truck that you need to find a wrench who really knows that particular rig. Places that say, "All Car Specialist" suck for diesel PU trucks. :)

I like specialist. I never go to those do all places. These are Duramax specialist in Orange County. I had the steering box and pump changed out due to this problem. Hard steering. I changed it because I didn't want to go on our long road trip and have it fail on us. A screaming wife and kids in sub 0 temp would not be a lot of fun. There isn't too many places for me to escape in that situation. I figure oil is oil as long as its rated and not some off brand?

For many applications, this is a true statement. In some cases, though, it really matters what oil or lube you put in. My Ford Superduty w hydroboost made noise on 3 different pumps until I put synthetic ATF in it. Some PS pumps are sensitive to oil. With a hydro system, it seems to be compounded, IME.

Best of luck w it. I’m actually installing the Redhead steering gearbox in my truck as we speak, I started the job in the afternoon and had to suspend operations to go rescue my neighbors whose car broke down 20 miles away. I think I’ll start another thread about that. :)

Im told by the mechanics the Redhead steering box are the best on the market so far but still not close to the original box that came on these trucks. The GM ones from the dealer will eventually go after about 50k miles. I can understand why can't someone make or rebuilt to original specs or better unless they go hog wild and get one from those off road places that cost thousands.

Good Luck with the rescue, Dennis.