bizarre powermaster behavior

[DentMan]

Hey guys a real odd behavior out of my powermaster hoping for some guidance from the forum

***Car is 10,800 mile survivor rarely driven. i think the accum bowl was original, it was much smaller than the cardone replacement i put on

1. hard brakes - blown fuse - replaced accumulator bowl. emptied and filled engine side fluid. I noted the pressure switch (grey) appeared to have some brake fluid inside the electrical plug in but didnt concern with it at that time

2. Turbotimmer forum member noted in a picture the engine side was awfully full so i extracted some fluid out

2. Car ran around town for about 4-5 miles and brake lite came on again - hard pedal - no brakes. small amount of fluid coming from somewhere, i suspect around the pressure switch but cannot tell for sure. it sprayed a little on the firewall, and trickled around the pump and master cyl. i washed it all away.

3. Here is the bizarre portion: I replaced fuse and began diagnostic per gnttype.com powermaster bullletin and when i cycle the key the pump stays on, the engine side of reservoir empties. when i turn the engine key off the engine side of the reservoir fills back up in about 60 seconds!!!!!

Here are my q's and I appreciate your guys time;

- can a bad pressure switch allow fluid from the accum bowl to come back to the reservoir

- can a bad pressure switch over pressurize an otherwise good accum bowl and ruin it?

- could the check valve allow fluid back into the engine side of reservoir

When i washed the fluid away from the engine bay i didnt note any significant fluid on the reservoir so i dont think fluid came from there. I noted fluid around the neck of the pressure switch.

 

[v6turbo87]

It sounds like your pressure switch is bad. It is what shuts the motor off when a certain pressure is reached. If the motor keeps running it could have over pressurized the system and damaged the check valve. Brake fluid in the connector of the pressure switch is a telltale sign the switch is bad. You could try a new switch and see what happens. I would not try a new accumulator yet. The new switch will (should) shut off the motor at the correct pressure. You can then see if the fluid drains back after it shuts off. If it does the check valve is probably bad. The pump should kick on again if it drains back and the cycle will start all over. Because the reservoir fills back up after the pump is off kind of indicates the accumulator maybe OK as it is what is applying pressure to the fluid to push it back through the check valve back into the reservoir.

 

[DentMan]

v6turbo87 thanks alot man; your opinion very much mirrors what I was guessing; its a 2 part problem. I just didnt (dont) know which direction the system flows. So a check valve could leave the "back door" open letting fluid come back up from the master cylinder. Ive read in a sticky at top of forum the physical location of the check valve is at the lower brake line engine side entering the master cylinder, and its direction of flow is from reservoir to master cylinder, can you confirm this?

 

[v6turbo87]

I can not confirm that. I switched to vacuum breaks long ago when my PM began giving me fits! Hopfully someone else will chime in on this.

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[BEATAV8]

Fluid in the switch connector = need new switch badly.

Pump runs without shutting off and reservoir fills itself back up quickly = lots of leakage. Need to rebuild the master cylinder and replace the internal seals (including check valve seal). The pump can also leak internally which would suck because it's very expensive, but its much more likely just the master cylinder seals.

highway stars has some switches in stock. The master cylinder rebuild seal kit can be bought from Karps Power Brake Service. It comes with everything you need.

The rebuild is very easy, just take it apart, replace the seals and clean and lubricate the parts with brake fluid and put it all back together exactly like it came apart. Hardest part of the whole deal is pulling the powermaster off the car and putting it back in.

The new cardone/Hydac accumulator you have should still be fine.

 

[DentMan]

v6turbo87 thanks.

Beatav8 thanks man. Ill start with the pressure switch and go from there. there wasnt much fluid to clean up so maybe the seals are still good. In any case would be a good idea to rebuild the MC. Ill keep this post active with my findings

 

[BEATAV8]

Once you have the unit freshened up with new seals, switch, accumulator..... change the brake fluid once per year and it will last a long long time.

I also try to discharge the system when I know it's going to be parked for weeks or months on end. Just shut the car off and lightly pump the pedal 20-30 times to discharge the accumulator pressure and unload the seals.

 

[gsgnnut]

save your money, the power master is a money pit and they are very unpredictable. Just read some posts on the near death experiences from these engineering disasters. Unless you want to keep it 100% original and you like to burn $$$, have a death wish, and like to constantly mess with PM's I recommend you convert to vacuum or hydroboost. You can aways keep the original PM on a shelf if you feel the need. I have had 3 near death experiences with PM sudden failures and have spent over $ 2000 on PM related rebuilds and repair parts over the last 20 years. The conversions are way less expensive than a rebuilt PM.