http://www.gnttype.org/techarea/brakes/PwrMstr.html

and it's telling you to replace your powermaster unit. Actually, it's telling you to rebuild your powermaster, as there's no need to buy the whole unit. The parts store rebuilds are hit and miss, and almost the same price as doing it right. If your switch tested OK, you only have to spring the $35 for the rebuild kit and $169 for the pump assembly, and you've got a new powermaster unit.

I decided to rebuild my powermaster system when it started making strange hissing noises and the pump was running almost all the time. It seems that the brake fluid slowly deteriorates the seals in the MC unit, and it starts to bypass the pressure it's intended to hold for your braking assist. The rebuild is not a difficult task, and the rebuild kit (part number 18020067 .. new number 18038510 and now costs $38.63 - editor.) is available from P&G Chevy www.partszoneonline.com , my favourite GM parts supplier. The pump is available from list member Hank Terry, who bought the original tooling from the general. He can be reached at http://www.members.tripod.com/Turbocars/pm.html The rebuild kit actually comes with great instructions on the piece-by-piece replacement, so this will just "round out" the whole procedure. You will need:

• Rebuild kit 18020067
• several unwanted rags
• Turkey baster
• empty 1 qt container for old fluid
• Deep socket set
• Set of micro screwdrivers
• Couple feet of wire
• 1 qt new DOT 3 brake fluid

1. Clean off a spot on your bench to put the entire powermaster assembly, and a "clean area" to actually rebuild the Master Cylinder (MC)
2. * Disconnect the battery*
3. Put on a fender cover. Brake fluid is extremely corrosive and will destroy your paint if even a drop gets on it.
4. Sit in the car and with the key off, pump the brakes 10-15 times.Odds are that if your MC unit is toast, it'll have no pressure to bleed, but go through this step anyway.
5. While you're in there drop the driver's side under-dash pad and reach up the brake pedal to pull out the cotter pin and washer. You can do this by feel, or grab a flashlight to see it.
6. Slip the pushrod off the brake pedal pin if you can.
7. Back in the engine bay, unplug the switch (top) and motor (lower front) wiring harnesses from the PM unit. I found it made life easier to remove the accumulator ball for access.
8. Pop the top off the reservoir and take a turkey baster or similar and suck out the brake fluid from the reservoir. Notice the funky black color? It's supposed to be clear! Be careful to avoid spills.
9. Put a rag under the brake lines at the MC and undo the front line from the master cylinder.
10. Have someone GENTLY AND SLOWLY step on the brake to force the rest of the fluid out of the MC onto the rag. Repeat for rear line.
11. Undo the two bolts that hold the unit to the firewall. Slip the unit forward enough to clear the studs, and move it towards the drivers side of the car as far as you can.
12. Hopefully you have a buddy who can crawl under the dash and help you slip the pushrod off the pedal. This is without a doubt the most ANNOYING part of the process!
13. Once you've got it off, wipe off all the brake fluid, lift it out of the car, walk it over to the bench and put it down on the space you cleared for it.

This is where the instructions included with the rebuild kit take over.Follow them carefully and you'll have no problems, but here's a couple of pointers:

1. When disassembling the unit, make sure you do NOT throw away the plunger thing with the spring, as you have to match it to the one of the two units included with the PM rebuild kit.
2. Push down HARD on the pushrod when wiring it down to remove the retainer clip. You'll see the whole assy move away from the retainer if you're applying enough force.
3. Getting the clip out is a royal PITA. I used a couple of micro screwdrivers to do it - one lifting out the end, the other tucked in behind to stop it from re-seating.
4. The drawings seem to be missing the thing that looks like a basketball inflator valve. Note where this thing is when you take it apart and be sure to put it back in when rebuilding.
5. The check valve retainer removal can be done with a screw - just tap it into the hole a quarter turn and pull it out. Other than that, the instructions show everything.
6. This is also a good time to put in a new motor/pump assembly from listmember Hank Terry. You'll eventually have to do it anyway, so you may as well do it now.
7. It's also a great time to make sure the wires heading through the speedo grommet are in properly and that the grommet is sealed on the firewall.

Once you've put the thing back together, you can bench bleed it, or just put it on the car and bleed it. I chose to do it all on the car to avoid the brake fluid drips.

1. Getting the pushrod back on the brake pedal pin will be your biggest challenge. Leave the unit off the studs while you try. If you have as much trouble as it did, here's a tip. You can actually pull the pushrod out of the back of the PM unit, as it's just held in there with a nylon ball in a socket.
2. Slip the pushrod with boot on the pedal and poke the end through the firewall, and put a block in place, or have a buddy hold the pedal down.
3. When bolting the PM unit back on, line up the pushrod to go back in the MC and finger tighten it. You'll reach a point where it's pushing back on the pedal enough that you can hop in and step on the brakes to reseat the push rod in the MC unit socket.
4. Once you've got it mounted back on the firewall with the pushrod on the pin, put some rags under the brake line holes and top up the reservoir with clean DOT 3 brake fluid. Don't use DOT 4, as my understanding is that it will eat away the seals in the system.
5. Let the fluid gravity bleed through the unit for 15 minutes (you can go clean up the colossal mess you've made to this point!)
6. Finger tighten both of the brake lines such that fluid and air CAN still escape, then have someone GENTLY step on the pedal.
7. Tighten the nuts, then have them release the pedal. Repeat until you're getting no air out when the pedal is pushed (watch to make sure the fluid level in the reservoir is adequate)* Top off the reservoir again and hook up the two wiring harnesses.Hook the battery back up.
8. With your can of clean fluid in hand, have someone turn the ignition to run. This will power the PM motor and the pump will suck fluid out of the reservoir to fill the accumulator ball. Add brake fluid as required to ensure the motor doesn't suck air. When the pump stops, you should have about 1/4" of fluid in the passenger side of the reservoir.
9. Turn key off.
10. Repeat the 10-15 pumps to pressure down the system and repeat the process above to make sure you have enough fluid. It's possible that the pump will have air in it and will displace the air with fluid over the next few cycles.
11. The brake pedal should NOT go all the way down - if it does, the MC still has air in it and you'll have to rebleed it.

Basically, you're done. Make sure you haven't introduced air into the lines (spongy pedal - you'll have to bleed the lines at the wheel if you do) and take it for a spin SLOWLY until you're sure you've got good brakes.Given the condition of the brake fluid, you should bleed the lines as well, but I needed a break and did it the following weekend.