(mods: FYI -- again, I didn't receive an external notification from the site on Mooseman's mention of me in post # 2)
OP: I see you're working with a Hydroboost system. They're not my favorite, because they run off the P/S pump, and when they go out, you lose power braking *and* power steering. GM puts them in their 3/4-ton and up trucks, as does F*rd and Ram. They're great when they work, but when they go out, you get about two brake pedal presses before the system goes out and you lose all power braking. Supposedly, larger displacement (as well as diesel) engines are marginal with vacuum, so the HB units are placed on those trucks that need 'no compromises' HD braking. (until the HB unit goes out, of course).
The seals inside the HB module go bad, and leak (usually, you'll see fluid outside of the unit, toward the back, due to the angle). While rebuild kits are available for cheap money, the one I got didn't make a damned bit of difference, and I followed the instructions to the letter. So I wound up replacing the whole unit, meaning I had to R&R it... twice.
To fix mine, I had to get a new HB module, then bench bleed the master cylinder (Dorman makes a kit for this; it's a few pieces of plastic and tubing and cost me about $15 USD -- and this was a few years ago; I'm sure it costs more now). I fastened the MC to my tool cart with a C-clamp, and bench bled it that way.
The nuts that fasten to the HB module studs are under the dash, and an absolute b!tch to get to, unless you happen to be on the smaller side. IIRC, I had to disconnect the brake pedal to gain enough room to get in with various swivel / flex ratchets to R&R the hydroboost module. Also, there's a gasket that goes between the back of the module and the outer firewall / bulkhead; don't reuse the old one. A new gasket should come with a replacement HB module (rebuilt or new).
There are three hoses that connect from the HB module. One goes to the P/S pump, with a dedicated outlet that 'regular' trucks don't have. The other two go to the steering box and P/S cooler (or rack & pinion unit, if your truck has that; mine is an '03, so I have the old school recirculating worm gear ('Saginaw style', if you prefer that description). You'll need a 16mm and 18mm flare wrench, as the two lines are different sizes. I found a combo 16 x 18mm on Amazon. And, of course, you'll only be able to turn the wrench a few degrees, at the HB module end, then reverse it. So start the two flare nuts by hand and tighten them as much as you can with your fingers. Those also have o-rings, so make sure they're present on both fittings, on each end. Again, new hoses should come with new o-rings installed. Make sure they're not twisted, or you'll have leaks after tightening the lines.
I tried to fill the new hoses with fluid before fastening them, but didn't have any luck. So... if you replace the hoses, fill the P/S reservoir to the tippy-top *before* you start the truck, or you'll instantly cavitate the P/S pump and introduce yet more air into the system. Once you run the truck for about 10 seconds, shut it off, and refill with fluid (I bought a US gallon of P/S fluid; it's cheaper). Get the front wheels off the ground, as well, as you're going to have to cycle the steering a number of times both ways, to get the air out of the system. The instructions that came with my new steering gear indicated 50x lock-to-lock, IIRC, although I know it didn't take that many to purge the air from the system, thanks to overfilling the P/S reservoir, and keeping it filled, as needed, while I purged the air out.
If you cavitate the P/S pump, even for a few seconds, you'll likely have to replace the pump, which is another big job, as you'll need a puller to get the P/S pulley off the front before you can remove the pump. And a bunch of labor to remove the accessory drive on that side. If it whines when you reach end-end steering lock, it's a good sign that it needs replacement.
Once you get all the air out, you can remove any extra fluid with a turkey baster, which you can get at your local dollar store. Also, get the mustard / ketchup bottles for another $1.25 USD; put P/S fluid in one of them and it makes it a LOT easier to get the fluid in the reservoir w/o spillage.
In my case, I wound up replacing the HB unit (twice), bench bleeding the master cylinder, replacing the three hoses, and (later on) replacing the P/S pump (I got the truck with over 200K miles, so I spent a lot of time / effort catching the thing up on maintenance). But once I got the HB unit / hoses in, and all the air purged, I then bled the brakes as per normal, and all was well again (and has been for about three years now, IIRC).
If you go as far as bench bleeding the master cylinder, just get a couple of large containers of your brake fluid of choice; you'll be able to get all new brake fluid in as part of bleeding the calipers. Finally, be sure to check your flex hoses before you start bleeding, and replace any that are marginal. From there, the only things left in the system are the hard lines, and the calipers themselves. It wouldn't hurt to give the hard lines a look-see and make sure they're not overly corroded -- if they are, now's the time to replace them, of course.
Yes, I wound up replacing a lot of parts; some of it was due to the miles on the truck, as I mentioned. Since I use it for towing, I wanted the truck to be as safe as possible (losing P/B *and* P/S is a pretty scary thing when you've got a 12,000 rig, in traffic.)
yes I tried tried the old schooll pedal method....no change. even parked it with the front of the truck up hoping the air might head up and out into the reservoir it did nothing
