Problem with new Power Master. HELP!

[Tow Man]

My original Power Master pump started blowing fuses so I bought a remaned PM from AutoZone. I had a local GM dealer do the installation since I have no experience with bleeding these units.

OK here's the problem. After installation, everything was fine for about a week. I parked the car for the last few weeks. Today I was going to take the car out and the brake pedal goes to the floor when you apply steady pressure. The pump cycles as it should but as soon as you apply pressure to the pedal it goes to the floor again. There are no fluid leaks visable anywhere.

Any ideas of what could be causing this? Is it possible it wasn't bled properly or do I have a defective master. Just looking for opinions on what could have happened. Everything was fine until I parked the car for 2 weeks!

Has anyone had problems with the A-1 Cardone rebuilt units?

[NC87GN]

I bought a unit recently from A-zone and it has held up well. That unit is very easy to install with some shadetree handtools, so do not be afraid to do it yourself. One thing to be careful of is make sure all the pressure is relieved from the system (PUMP brake pedal 10 times with car off).
If your planning on just bleeding the brakes this may help.. Bleed the brakes at the rear starting with the passenger side. Open the brake bleeder from the backside of the backing plate and run a hose to drain fluid/air into a 2 liter bottle. Turn the ignition on and hit the brake pedal to the floor and HOLD IT. Have another able body tighten the bleeder first then let your foot off the brake pedal . Repeat this process until all the air is out of the line. HTH


Mike Banas
87GN

[turbofish38]

It does sound like the PM has gone out again. Usually when there is excessive pedal travel there is fluid leaking past the o-rings on the pistons. If your dealer has the special pressure gauge they should be able tell right away. Dumb question, does the PM pump keep running or does it cycle normally?

[Tow Man]

Originally posted by turbofish38
It does sound like the PM has gone out again. Usually when there is excessive pedal travel there is fluid leaking past the o-rings on the pistons. If your dealer has the special pressure gauge they should be able tell right away. Dumb question, does the PM pump keep running or does it cycle normally?

Hey Eric, the pump cycles normally, but when you put your foot on the pedal, it steadally drops to the floor. I still haven't had a chance to mess with it or take it back to the dealer. I was hoping that maybe some air trapped in the system worked its way back to the master after sitting for some time. Just wondering if anyone else has experienced this.

[gofstbuick]

Before you condemn the PM unit, look under the car, behind the wheels. Is there any brake fluid dripping from the disk brake calipers or from the wheel cylinders? If not then the MC is probably defective. Probably not the power assist part, but the actual master cylinder. It's probably leaking past one of the seals in the bore, or the bores are pitted. In which case, you'll need to remove the PM unit, take it back to where it was purchased and warranty it. As others have stated, you should not be afraid to change it yourself. If you need help during the installation process or are unsure, email and I'll shoot you a phone number or we can walk through it via email.

[Tow Man]

Thanks for the offer of help, I may take you up on that phone call if needed.

Fluid leaks were the first thing I looked for. There is no leakage visable anywhere. Just my luck to get a defective unit
I will pull the unit out and return it for warranty.

I also noticed that A-1 Cardone insists on replacing the proportioning valve to the brass unit along with the PM. I never looked to see which one I have. What affect can a prop valve have on the PM? They insist you replace it but don't say WHY

[V6POWER]

turbofish38---What should the pressure read for a good unit?

[gofstbuick]

I posted this a while back, regarding making the adapter for a set of brake gauges. The pressure readings are around 700 psi and you need to bleed pressure off the reach the PM switch turn-on pressure. the brake gauge has a bleed port to allow you to bleed pressure and fluid back to the master cylinder reservoir to match the turn on pressure. You need to follow the flowchart in the factory manual, and use a set of brake pressure gauges tee'd into the pressure switch or accumulator.
"I have heard of people using the other (less expensive accumulator) with great success. The flowchart I have seen is from the factory service manual. It relates to pre-charge pressure. You need a set of brake gauges and you need to make an adapter. The adapter is a 1/4 NPT tee. It will have 2 female ports and one male port. Change female port on the top to M12x1.5 thread pitch. DONOT use a helicoil, use a time-sert, keen-sert or thread insert. The helicoil will leak. Order a hydraulic adapter to change the male port (directly oposite of the female port with the thread insert) from 1/4 NPT to male M12x1.5. Leave the other female port alone, this is the port used to attach the brake gauge. This adapter will allow you to remove the pressure switch, install the adapter, install the pressure switch on the adapter and connect a set of brakes gauges to the adapter. You can then hook the electrical connector back up to the pressure switch and check accumulator pre-charge pressure and pressure switch on time (using the specifications from the GM service manual). By the way, if your feeling really rich, you could order the factory GM tool from Kent-More ($479). The tool I'm using cost approximately $130. Ordered a set of brake gauges from Harbor Freight tools for $93, adapters cost $8 (local hydraulic shop) and machine work was $20."