Any ideas on this? Also - possibly important to note. This is on my 2003 6.0 H2 which has a full time AWD transfer case with 4Hi (normal mode), 4Hi Lock, 4Lo Lock (and Eaton air locker for the rear axle that can be activated in 4Lo lock), 4L65e (slightly, very very slightly, beefier version of the 4L60e - I think some of the HD trucks with the 6.0 also have the 65e).

Twice now in the past week. All of the sudden the steering becomes very tight. If I stop while it is like this and try to turn the wheel I can barely move it and hear a hissing sound but not as loud or distinctive as the whining sound you hear from an empty or very low on fluid power steering pump. Where it gets weird though is it acts like the drivetrain is wound up as if the front and rear diffs have different gear ratios in them and everything starts to bind up or like its in 4Lo locked up and trying to slow turn on asphalt. If I try to turn the wheel with much force (wheels maybe turned a half an inch is all) and then try to move the truck does not even want to move almost as if I was holding the brakes. It will move if I let go of the wheel and let it start off straight and at speed drives okay but I can still feel some tightness of the steering. All 4WD functions are fine and I can cycle it to 4Hi Lock, 4Lo Lock, lock the rear diff in 4Lo, etc and even doing that everything still acts bound / wound up. First time a couple of days ago I drove it on home like that (about 25 miles) and the next morning I checked the power steering and brake fluid - brake because I reckon it could be something to do with the hydroboost and both were fine and it drove fine. This morning coming into the shop was fine until about a quarter mile before I got to the shop it started it again.

Just not really sure on this one. Hyrdroboost? Transfer case? Torque converter or transmission? I need to have this on the road but I do have another vehicle I can drive (my GMC Sierra is in pieces right now) but its an older 1999 Blazer and it needs updated injectors.... it runs and drives okay but falls flat on its face and bogs down if you give it more than about half throttle.

 

Hydroboost not drivetrain imo, not an expert in hydroboost but sounds like there is a valve or bypass sticking and not diverting to steering and making the brakes stick..

 

I think you are right..... I rebuilt it about a year ago and it seemed to be fine since. This morning I had a little more time to experiment. Turning the steering wheel while sitting there idling, you can physically watch the brake pedal go down when you do so. I pulled the master cylinder bolts loose and backed the cylinder off the hydro and the brakes released so yeah, the hydro is apparently failing in some manner.

After reading many posts about self rebuilds and off brand store bought rebuilt ones leaking or being problematic I'm going to bit the bullet and go ahead and order an ACDelco one and get it over with. Will at the same time flush the PS fluid as well just to be sure there is no sort of contamination (fluid is clear but starting to get a tan tint to it).