Strong Hydroboost - but no Power Steering? (2002 Suburban 2500 8.1L)

jpeterferrell · April 18, 2022

Hey everyone! I'm brand new to this forum, and brand new to the GM world, but have run into an issue with my 2002 Suburban 2500 (8.1L) that has me completely stumped. First, a bit of background:

I have been slowly doing a complete front-end rebuild on the truck over the course of the last year or so. I had 215k on the clock, and while the rig was very well maintained generally, it was in pretty dire need of a suspension and steering refresh. So, here's what I've done already:

1) Kryptonite UCAs

2) Kryptonite LBJs

3) MOOG lower ball joint bushings

4) Kryptonite inner and outer tie rod ends

5) Bilstein 5100 shocks (front and rear)

6) Kryptonite Torsion key leveling kit

7) Kryptonite Death Grip Pitman Arm

(8) 2011+ AC DELCO Hydrobooster

9) New AC Delco Brake master cylinder and reservoir

Then, I replaced the power steering gearbox with a BlueTop unit. Everything seemed to work fine initially, it took me awhile to bleed the system, but I am positive I have all the air out of it now. I also replaced the two high pressure power steering lines while I was at it (both were clearly slowly leaking/weeping). Now, after having everything completely aligned again, I've run into what seems to me to be a bizarre problem. The P/S pump doesn't whine any more than normal. The Hydroboost works strong (very strong after the 2011 upgrade). BUT, when sitting still, I have virtually no power steering assist. I can't turn the wheel left to right at all. Start to move (really, even the slightest bit) and it frees up and I can go along.

At first I thought I must have gotten a bad steering gearbox - but this assist problem is extremely intermittent. Sometimes, I can turn the wheel stop to stop while sitting still, no problem. Other times, I can't do it at all. The hydroboost works perfectly fine, and perfectly consistently. The pump doesn't sound like it's whining. The fluid level is perfect. Anyone have any idea what could be causing this, before I go throwing more parts at it...?

David89GMC · April 19, 2022

Why did you put 2011 parts in a 2002 vehicle? Did you replace everything in the power steering and hydroboost 2002 with 2011 parts? Newer doesn't mean upgrade, it most likely means incorrect. Even in 2002 there are several different power steering pumps, with different connections. I did my '03 2500HD and had to learn this before ordering a new pump.

Hate to say it, but get the correct parts for your vehicle and try again.

Or ask Blue Top to help with the problem. Even their website shows very different steering gear models between the "2011 upgrade" and your model year.

jpeterferrell · April 19, 2022

Sorry, I should have been more clear. I used a hydro boost from a 2011 - it's a well known upgrade part over the 2002-2010 models. The hydro boost works great - bolted right up, fittings went in perfect, brakes way better than before. For the same reason, I don't suspect the pump (which I haven't changed at all), since if the pump was bad it seems like they hydro boost wouldn't function either.

I'm going to try bleeding one more time, then I'll contact BlueTop. Seems weird that the gearbox would "work" perfectly fine, not make noise, etc, but just have no power assist? I did retrace the lines to make sure I hooked them up right, checked for leaks, checked the condition of the fluid, and all of that seemed good. I'm really hoping I'm just working out some larger bubbles that had found their way into the gearbox and sat there for awhile...

shakenfake · April 19, 2022

6 hours ago, David89GMC said:

Why did you put 2011 parts in a 2002 vehicle? Did you replace everything in the power steering and hydroboost 2002 with 2011 parts? Newer doesn't mean upgrade, it most likely means incorrect. Even in 2002 there are several different power steering pumps, with different connections. I did my '03 2500HD and had to learn this before ordering a new pump.

Hate to say it, but get the correct parts for your vehicle and try again.

Or ask Blue Top to help with the problem. Even their website shows very different steering gear models between the "2011 upgrade" and your model year.

Hydroboost is a common upgrade on these years. It is an upgrade and not a mistake.

What p/s pump are you running?

I am assuming you did all the proper connections? I would perhaps switch to an OEM p/s pump out of an Escalade with hydroboost since it has all the connections for the hydroboost into the p/s pump instead of teeing in like normal.

newdude · April 19, 2022

If I recall correctly (and someone correct me if I'm wrong), brakes are the dominant item in the hydroboosts if there is an issue. If there is an issue, the accumulator will have about 2-3 stops worth of fluid stored to stopping.

That said, I'd still be suspect of the PS pump, especially if its original. It might not be making any noise, but perhaps it doesn't have the a$$ to power the new booster and the new gearbox, or I should say enough to power the booster but the gearbox suffers.

jpeterferrell · April 19, 2022

This is definitely possible. The pump DOES look to be original, before I started swapping parts I did a full flush, and the fluid coming out was horrid looking (straight black). The hydroboost is definitely functioning perfectly fine, and the loop does go pump --> hydroboost --> steering gear. I can absolutely see the pump just not supplying enough overall pressure to work both the upgraded hydroboost and the new steering gearbox, particularly when I have much heavier inner/outer tie rods/pitman arm/idler arm bolted up.

I was going to buy the PSC SP1404 pump as my replacement...anyone have any experience with it? Should I go with that or a stock AC DELCO replacement...? Cost is...more or less the same between the two, but the PSC looks like an upgraded unit..

shakenfake · April 20, 2022

I would buy the stock AC Delco personally. I don't know anyone with that PSC pump nor do I have any experience with it.

Just out of curiosity and testing reasons why not disconnect the hydroboost from the power steering just to be on the super sure side that the hydroboost is not causing the issue. The reason I ask this is because the stock pump normally is plenty fine to supply the hydroboost.

davester · April 20, 2022

...not sure if the high-pressure line that goes from the pump to the hydroboost will be able to screw into the steering gear (which is what you would have to do to bypass the hydroboost)...

jpeterferrell · April 21, 2022

That's exactly right - I think without some kind of specialty tool (basically a bypass block), which I'm not even sure actually exists, there's no way to just bypass the hydro boost altogether. I really don't want to just throw parts at this thing, but it also seems there may not be a way to easily diagnose it for a shade tree type like myself. I'm going to double-check all the fittings this weekend, maybe do one more bleed (maybe even flush from the hydro boost?) and see where I'm at. After that, I may have to resort to professional help!

shakenfake · April 21, 2022

Just put on the stock hoses for the power steering.?

I don't really understand why you couldn't bypass the hydro boost. All it is is a couple of added hoses from PS to the master cylinder. Just unplug and cover all the holes.

jpeterferrell · April 21, 2022

My fault - the vehicle has hydroboost stock. I just upgraded the unit itself to an upgraded part from a 2011. The stock hose routing requires it going through the hydroboost.

shakenfake · April 21, 2022

Okay, see I thought that 2500s all had it stock but your first post made me rethink that.

I am thinking it is the pump though it it is working under load but not working from a stop.

davester · April 21, 2022

I know for my 3500/6.0, it really sucks to change the output hose from the pump, which is what you have to do to swap that line...probably sucks even more with the larger 8.1

jpeterferrell · April 28, 2022

UPDATE: I've done some experimenting, bled the system several more times, flushed the fluid, and think I've got it diagnosed.

I get steering and braking as I would expect in virtually every condition, with the sole exception of while stopped, with the brake applied. In that situation, I have ZERO steering assist. I can't turn the wheel at all (at least not without extreme force applied). When I try, the power steering pump complains, groans, whines. If I put the vehicle in park, take my foot off the brake, but remain stationary, I get power assist back - I can turn the wheel stop to stop.

Lift off the brakes, put even the slightest bit of throttle on, and it's even less of a problem - I get steering assist, enough for me to generally navigate around no problem (although not as much boost as I would expect). In all conditions, the assist seems not quite like what I would normally expect for a truck like this, that and my "return to center" after turning isn't nearly as strong. So, I still suspect I have a power steering pump that just can't keep up with a new hydro boost and a new power steering gear.

I'm going to have a shop replace the pump next week and we'll see where we are!

vucelick · April 28, 2022

Had the same issue on my 2001 8.1 The current version of the power steering pump has a new lowspeed bypass valve design that gives you more boost at slow or no speed. Make sure you get the latest factory gm pump. Backing my boat up the driveway was a real chore, now its much better.

Edited April 28, 2022 by vucelick