SOLVED! HydroBUST(ed); or, how to R&R yours

Reprise

Original poster
Lifetime VIP Donor
Supporting Donor
Member
Jul 22, 2015
2,724
Posting this in hopes someone might have gone through this, and can chime in while I research further.

As part of my build, I purchased a seal kit for the hydroboost module in the Sierra, because fluid was coming out of the weep hole (square / notched area on the bottom, facing the ground).

Installed it without any issues (I didn't even have to unmount the back end of it off the firewall). The seal in question is the power piston seal). Made of rubber. Installed per instructions. There's two different types, depending on the year of the module; I know (?) I ordered / installed the correct one (and in the correct direction).

Anyway, it worked - for about 20 min of cam break-in in the garage, and 20 minutes of driving, at which time, I noticed a groaning at application of the brake, while stopped at a light. Not long after, started progressively losing power steering (so I knew what was happening, of course.)

Wasn't far from home, got it back ok (btw, I didn't 'lose all braking'; just the power assist - but that was bad enough, coming to full stops).

When I parked, I could see a path of fluid drippings behind the truck; a quick look under the truck showed it basically pouring out. Shut off the motor, and went inside (as it was dark, and I had just put the Envoy in the garage for rear axle seal replacement.)

Went out this morning, and there was no hose issue (I'd pretty much replaced them all, anyway), no broken / corroded metal lines, no loose connections, etc.

Checked the HB module, and sure enough, it was plenty wet by the weep hole, with the tell-tale sign of fluid residue directly underneath. AFAIK, it *never* leaked as badly as it did last night -- at least, not while I've had the truck.

I'm guessing I'll have to replace the whole mechanism, and will start down that path. But if anyone has successfully repaired one of these things, feel free to chime in. Thanks!

PS: I do have some pics from when I replaced the one seal, and can snap more, if requested.
 
Last edited:

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,639
Tampa Bay Area
This Video may offer some additional Help and Information on How to Re-Build this Unit:


...and few more with some Additional " tear Down" and "On The Bench" Views and Angles:


THIS Information is VERY IMPORTANT TO KNOW!


Also,,, Not certain that THIS Particular Diagram is the EXACT Same Design as your particular Hydro-Boost Unit is... But it will give a General overview of what the Internals Look Like:

HYDROBOOST2.jpg
 
Last edited:
  • Like
Reactions: Reprise

Reprise

Original poster
Lifetime VIP Donor
Supporting Donor
Member
Jul 22, 2015
2,724
Thanks, @MRRSM :tiphat: I'm familiar with some of that material. I was actually able to remove / reinstall my HB unit without having to do the crawl into the cab (and it was made easier by having the extra room in the engine bay w/ the heads off, etc.) A 3/8 12-point works well to loosen the five star-shaped housing bolts, if anyone else tries to service one of these things.

Since the vendor of the repair kit invited comments / questions via his website, I've sent a note his way to get his opinion on the matter.

Re: the diagram you posted - they didn't change too much over the years, and all of the 'big 3' used them in their light / medium duty trucks. I like the concept & understand the usage -- but it's a little disconcerting to lose both braking and steering assist at the same time. :yikes:

Will post back once I have a solution in place.
 
  • Like
Reactions: mrrsm

Reprise

Original poster
Lifetime VIP Donor
Supporting Donor
Member
Jul 22, 2015
2,724
No response from the kit seller; gave up and ordered up a new (GM) unit today. $335+tax, no core. Splurged on a new mounting gasket for $8 ... LOL. They'll be here Saturday.

Could've gotten a reman (Cardone) for about $150, but saw reports of "leaking after a year", etc. - and since this provides boost for brakes *and* steering, I spent the extra coin for peace of mind while towing.
 
  • Like
Reactions: mrrsm and Mooseman

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,639
Tampa Bay Area
Small h/j...

You've probably already got this indispensable GearDrive Chrome-Vanadium Dual SAE - METRIC Flip-Side Flare Wrench Kit at an excellent low price.

But jik other Folks are Wrangling with Flare Fittings For The First Time and have no such tools ...or need to unfasten and re-fasten such lines and cannot determine their proper wrench sizing differences:


GEARDRIVEMETRICSAEFLARESET.jpg

SAE to Metric Conversion Chart Where "Close Is Good Enough":
 

Attachments

  • socket-wrench-sizes-conversion-charts-gs-e.pdf
    176.8 KB · Views: 1
  • Like
Reactions: Reprise

Reprise

Original poster
Lifetime VIP Donor
Supporting Donor
Member
Jul 22, 2015
2,724
Yep - I have a 16 x 18 mm flare wrench I keep on hand for this. Had to get it thru Amazon; I have both a Craftsman set, and a HF set, and neither had a 16mm or an 18mm in it, nor did HF sell a set with those two sizes.

Thankfully, I was able to get the one wrench that incorporated both sizes. As for why GM used both sizes - one is for the steering feed (larger line); the other for the brake. At least, I think that's the how / why of it.

And someone needs to come up with an open-end / flare wrench that lets you move the wrench more than 1/8" at a time, and not have to flip it on Every.Single.Turn.
Although I suppose someone would've come up with that, already, if it were feasible.
 

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,639
Tampa Bay Area
ALL Flare Nut R&Rs are complicated by these Six Issues:

(1) Most Flare Nuts will have previously been installed with Excessive Torque.
(2) Flare Nuts are NOT robust enough to resist being Twisted Out of Shape.
(3) Flare Nuts are made of MILDER STEEL & since NOT Solid Hex... Easily Fracture.
(4) A Flare Wrench MUST create a RIGID THREE POINT Structure around the Nut.
(5) It is only SHEER LUCK that using Dual Flat Wrenches Do Not Ruin them ALL.
(6) Flare Nuts - Fasteners are invariably getting Exposed to Corrosive Liquids.
 

littleblazer

Member
Jul 6, 2014
9,265
Had a Cardone in the escalade for... 2 years now? Worked fine. :tiphat: I could get 3 for the price of one delco lol. Booster isn't hard to replace. 1/4 inch swivels to get to the nuts inside. Your hand will get cut up. But not a terrible job. Maybe an hour. Be careful of the brake light switch. Mine fell apart trying to reinstall.
 
  • Like
Reactions: mrrsm

Reprise

Original poster
Lifetime VIP Donor
Supporting Donor
Member
Jul 22, 2015
2,724
(This procedure covers GMT800 trucks with Hydroboost systems; (99-06); 07-up similar)

So I got the booster / module R&R'd. Some notes...

- Get a new gasket ($8), along with your new booster.

- You'll only need one socket for the entire job - a 15mm deep.
- 1/2" drive is a bit bulky, under the dash; 3/8" would probably work better.
- You'll definitely need some combination of wobble extensions (shorter the better), universal swivel, flex-head ratchet. Bring 'em all to the party. Some may work better for you in a particular location than others.
- A pick tool or small flat screwdriver will help with the retaining clip & rod removal.
- Some form of lighting is definitely needed. Flashlight, small spotlight, etc. Emphasis on small, because you don't have a ton of room to move around under the dash.

First, disconnect the underhood side. 16 & 18mm flare nut wrench, pliers to loosen the clamp on the rubber return hose, and the 15mm socket on the two nuts that connect it to the brake reservoir.
Don't disconnect the brake lines - not needed. There will be enough slack to pull the reservoir forward and off the two studs. But leave it as-is, for now, once you get the nuts removed.

Now take all of your sockets / extensions, and head inside the cab.
Remove the knee bolster / kick panel, with a phillips screwdriver & small socket (mine was off already... sorry I forgot about the other socket!)

Depress the pedal several times until the compressed gas reserve is exhausted. This is important to do, before you disconnect the booster from the pedal.

Move the seat back as far as it will go. If you want to recline the seatback, that's fine, but not a must.
If you have the power seat, disconnect the fuse, as it's easy to trigger the fore / aft switch when you lean under the dash. But truth be told, you better be ready to work on your back (really, your shoulders!), looking up at your work. And you better be fairly dextrous with your left hand, as it's going to be doing most of the work.

Flip the steering wheel all the way up, so you have room to extract yourself.

Looking from the cabin end, it's pretty easy to tell where the studs / nuts are for the booster. Look for the rod that connects it to the pedal. There's a retaining clip. Take that off first. Be aware that it may go flying (mine did). A replacement costs $8, most places. If you think I'm spending $8 for a clip, dream on. I'll use a zip tie for a few days, till I find another.

Now you have a brake switch surrounding the rod. Your job is to extract rod from pedal, without breaking the switch assembly. It's not too difficult, just don't try and gorilla it off.

The easiest way to get the rod and switch assembly out in one piece:

Take one hand (left, for most people) and grab the rounded portion of the rod, firmly. Take the other hand, and put it behind the far side ('back') of the plastic switch assembly.
Now, start wiggling the rod and switch toward you, alternating pulls between hands.

If this is the first time your HB is coming out, expect that the rod will be somewhat stuck on the pedal, and it may take a bit to get it to start moving. But once it does, both rod and switch should come off without too much trouble.

<picture goes here>

The one side of the brake switch has a slot cut out on the one side. By turning it, it allows you to lift the one side while gently moving the other side and remove it from the rod. Note that the brake switch connector & wiring was pointing downward - it's easy to put it on backward (and wonder why it doesn't fit as well on reassembly). Ask me how I know.

Moving the brake pedal toward the firewall will make this process much easier. If you didn't discharge the residual pressure from the booster earlier, do so now; the pedal will be much easier to move.

Once you get the rod / switch off, take a look at your four studs / nuts. The one on the bottom LH side (as you face the pedal), close to a metal brace, is by far the hardest one to get out. You can remove that brace if you wish; a couple of bolts hold it in, and it slides out. I did NOT remove this brace, so you *can* get the nut off that stud, with it in place. But it might be easier, if you remove it.

There shouldn't be TOO much torque holding the nuts on. Once you get them broken, and a few turns in with the ratchet (which you won't be able to swing too far; a flex head does help), you can turn the socket with your fingers (short extensions may come in handy for this). It will seem like forever until you free the nuts from the studs. Keep turning!

Once you get all four nuts off (the last one will also be a pain because the booster housing will start moving / shifting), crawl out from under the floor and head back under the hood.

Now, move the three lines you disconnected earlier out of the way, and gently pull the brake fluid reservoir forward till it clears the studs. With this, you'll have enough room to pull the booster forward and out from the firewall. You'll need to twist / turn it a bit to get it out, but it's not hard. And you can easily stand on the ground / floor while you do this.

Take your new booster, and make sure the rod end matches your old one - there are two different ones. One has a squared-off end; the other is more rounded. If they differ, it may not fit properly.
Take your new gasket, and place over the studs on the new booster. It'll stay on until you can twist the new one into place. Or, put it on after you get it in the engine bay, but before feeding the rod / studs through the firewall. Whatever is easiest for you.

Get the booster in as close to the firewall as you can, but you *don't* need to have it exactly flush on all four ends. It'll stay in place while you head back under the dash.

Thread at least two nuts on their studs; this will keep the booster in place, but it really doesn't move. If one of the studs is crooked, or barely through the firewall, leave that one for last. Drawing the other studs onto the nuts will bring that odd one in. Or, you could use a needle nose pliers to pull it in, as well.

As with most things, reassembly is the easier part. I was able to get three of the four nuts threaded most of the way with just the socket and my fingers (left hand). Then hook up your socket wrench and tighten them down. Not really tight. 'Sortatite', if you're using German torque specs (I did).

Once you've got the four nuts tightened down, it's time to reattach the rod & brake switch.
With the wiring / connector facing downward, position the holes on either side of the rod. You can turn it a bit upward, to take advantage of the slot on the one side. Just make sure its 'finished' position will be with the connector facing downward.

Bring the brake pedal inward, until the stud portion is lined up with the holes in the rod / switch. Then push the assembly onto the brake pedal stud, making sure the stud on the pedal enters the 'blind' hole on the brake switch, before the rod (the two ends of the brake switch 'surround' the rod, on either end.) If the one end of the plastic housing starts pulling away from the 'open' side, back off a bit. You can break it easily, and if you do, a new switch will cost $15-30 or so, and you won't have brake lamps until it's replaced. No, I didn't break mine!

Once everything's in place, push the rod & switch onto the stud as far as it will go. You can swing the switch downward into its resting place, now.

Before putting the clip back into place, depress the brake pedal; you should see the reflection of the brake and CHMSL lamps. If you don't, recheck how you connected the brake switch, make sure the connector didn't pull out of the switch, etc.

Once you've verified you have brake lamps, then reattach the clip. You're done with this portion, except for reattaching the knee bolster panel.

If you had fluid in your system before pulling the HB, then at least top off your P/S fluid. Raise front wheels, bleed, check for leaks, repeat top off as needed, done.

If you're replacing the HB (or hoses, or P/S pump) because of a catastrophic leak... there's going to be a lot more air in the system. Better to do this... \/

Fill the P/S reservoir to the top and leave the cap off (don't worry about the 'full' mark; put the fluid almost up to the top of the neck.) Reconnect the three lines, the brake reservoir assembly, and tighten up everything. Start the truck and check for leaks at the connections. Then bleed the air out of both the brake pedal and steering, as per procedure (you can look this up, or follow the manufacturer's directions, if they provided them.) Add fluid as needed. If you start seeing foam in the P/S reservoir, shut off the engine and wait 30 minutes. Then check the fluid / level, restart the truck, and continue bleeding.

Note that when you take the truck out, you may find the steering is more difficult, especially when turning the wheel a large amount, like a 90 degree turn left or right (if so, it still has some air in the system).
Be prepared for this, so you aren't taken by surprise.

The system *will* self-bleed (provided there's enough fluid), but it'll take a bit of time / miles (about 20 -?) until you get the proper assist back. Or, head back home and bleed some more, if it's really bad.

Recheck your P/S fluid level, once all the air is out of the system, and you're done.
 
Last edited:
  • Like
Reactions: Mounce and Mooseman

Reprise

Original poster
Lifetime VIP Donor
Supporting Donor
Member
Jul 22, 2015
2,724
So, as it turns out, I got hosed by AC Delco. Or maybe, I should say "orificed"...

Turns out that my HB -> steering box hose (a high-pressure one) came loose (I had heeded MRRSM's advice not to gorilla tighten the flare nuts -- and, no, I don't blame him -- it wasn't him turning the wrenches).

Anyway, I started up the truck in the garage (hood up), and immediately saw a re-enactment of Buckingham Fountain taking place in the engine bay. Immediately keyed off. We're talking like 1 sec to realize what happened, and 1 more sec to key off.

When I say the fluid was all over the D/S fender, the front bumper, basically the whole left side of the underhood area... I'm not kidding. At least I know the P/S pump is still working, eh?

Anywho... I go to reattach the flare nut in question (the 16mm side), and find out... I can't get it started. Checked the threads; they looked ok. Checked the orifice threads (by feel); seemed OK.

Thinking I stripped the flare nut, I ordered up a warranty replacement for the hose, from Rock (up to now, the new hose had been just fine). Then I got the idea to try that line in the old pump, since I still had it, and didn't have a core to return.

Sure enough, the thread is buggered up on my 'brand new, not re-manned, not customer returned' gin-u-wine AC Delco hydroboost unit.

Had to put in a reship / return for that one (got it from Amazon; the new one will be here Wednesday, and you can be damned sure that before mounting it to the firewall (again, upside down in the cab), that I'll verify both of the high pressure fittings screw down properly into the new unit.
 
  • Angry
Reactions: Mooseman

mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,639
Tampa Bay Area
I'm very sorry that such a Labor Intensive Repair has gone sideways for you. Anyone who has had to R&R any Rack & Pinion Steering Unit ...cringed upon reading this. The link below contains more precise information of how much force is nominal for a wide range of Hydraulic Flare and Compression Fittings.

We've ALL had to rely upon a "Best Guess" when it come to "Knowing When to STOP Turning..." and either Tightening (or Loosening) these Fittings and these events ALWAYS occur in places that are both Impossible to Access and Impossible to Clearly See. Flare Fittings are notoriously unforgiving... and ALL of us have been caught in this Trap at one time or another.

This information is worth saving in anyone's "Mechanic's Library":


As a General Rule,,, Be Suspicious whenever possible before installing New Hardware of any Hydraulic Operation. Closely examine both interfaces in between the Hose Fittings Swaged Piping Flared ends and their intended Port Receptacles for any Nicks, Burrs, Bent Piping or find ANY Prior Damage caused by other Buyers who have subsequently RETURNED such Hoses to the Auto Parts Stores to be Re-Stocked and Re-Sold to the Unsuspecting,
 

Reprise

Original poster
Lifetime VIP Donor
Supporting Donor
Member
Jul 22, 2015
2,724
Thanks. As it turns out, I had originally tightened that 16mm fitting about halfway down, mostly by hand (it stopped about the same point that the 18mm did, on the other side. But instead of 'gudentite', I stopped at 'sortatite', with the wrench. I know for a fact that I didn't cross-thread it.

But now, when I try to reattach it, I can't even really get the fitting started. And as I write this, I *just* realized why (?)

The fitting must've nicked or otherwise damaged the threaded orifice, when the pressurized fluid forced it out. Too bad it couldn't have been the fitting that was damaged, instead of the orifice. Easier to replace the hose, for sure.
 
  • Sad
Reactions: Mooseman

Forum Statistics

Threads
23,271
Posts
637,476
Members
18,472
Latest member
MissCrutcher

Members Online