Powermaster Rebuilt. No pedal pressure.

Jon Early

Active Member
Dec 4, 2014
Hello everyone,

I am scrambling to find a small miracle that will allow me drive to Nats on Wednesday. I'm hoping some powermaster gurus will be able to help me out.

The car had a brake light when I bought it in August. It stopped fine, but sometimes the assist wasn't always ready when I needed it. I changed the accumulator and then tried to bleed it, but then I had no pedal and the motor ran continuously.

After that I bought the reseal kit from Kirban. This powermaster was a mess. The check valve seals were awful, and one of the springs was installed out of order. After replacing all the orings lapping the valves, bench breeding, and bleeding all the wheels there was no change in symptoms. The motor just kept running, and the pedal went to the floor when the key was turned.

By this point I was beyond flustered. I gathered some fittings, so that I could hook up a pressure gauge to where the pressure switch is normally threaded, and I witnessed the pressure rise up to a little over 500psi and stop even though the motor continued to run. This leads me to believe that the pump is no good, but it doesn't explain why my pedal is so soft. I've bled the system over and over again with the prop valve held in, and I m not seeing any air.

Are there any other hints as to what could be happening before I give up? I'll be pretty bummed if I can't make the trip down.
Sounds like the pump is unable to build pressure. The pressure switch won't turn off the motor until something like 700 psi, and then it will switch it back on again at around 500 psi. So, in your case, the motor runs continually due to the inability to achieve the required shut-off pressure. The pump and motor are sold as one unit, although I have separated them in the past. I once had bought a so-called "rebuilt" motor and the motor was no good, but it had a good pump, which I swapped onto my old, but good motor. The powermaster can be a hassle but I still keep mine in working order. Pick up spare parts when you can find them cheap. Good luck!
And you don't need to hold the prop. valve in while bleeding this system.

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Thanks guys. In the last hour or so I finally got some air out. The pedal feels normal but the pump is still doing the same thing. I've tried looking for spare Eh pumps, but can't seem to find them separate from a whole remanned powermaster. Do you have a link to any or do I have to find a used one?
I've seen just the motors for sale on oldbuickparts.com, however it's like $450.
Try listing in the "parts wanted" on this forum.

Watch the fluid level on the pump reservoir side. When the pump starts, the fluid level will drop. If all was well, the fluid level would drop and stay low until you hit the pedal. However its probably leaking fluid back into the reservoir. To check, turn the key off and watch the fluid level. see if it's rising when the pump has stopped. if it is leaking back into the reservoir, it can only come from 2 places. In the reservoir there are 2 ports. Place a finger over each one and see where the leakage is coming from. You can feel the leak even if it's very slow.

if it comes from the pump supply port, then the issue is the check valve The check valve is hyper sensitive to even the most minute tiny debris or imperfections in the poppit or seal.

if it comes from the master cylinder return port, then the issue is inside the power booster section of the master cylinder.
Thanks for that! I read something similar elsewhere, but it wasn't covered in as great of detail.

Something happened between the first time I started it up earlier today and now. The fluid in the reservoir doesn't drop very much, and the brake light doesn't turn off anymore. I can't really feel anything coming out of the ports, but I don't think very much is going into them anyway. It's baffling how finicky these cars are.
I can definitely feel suction when the pump is running though. I really don't want to buy another oring kit and rebuild this thing again, but it seems like that's my remedy.
Sounds like you're having an issue a little similar to what I had. I rebuilt my PM last week and i thought everything went well, and seemed OK after a couple simple tests after install. But backed out of the garage and all of a sudden the pedal went down and the motor started running constantly with a brake light lit.
So, pulled back in the garage to look see what happened. Nothing looked out of the ordinary except that the passenger side reservoir (the one that should go down when the system is working) was nearly full while the motor was running.
Turned the key off, removed reservoir lid, turned key on and saw that fluid was flowing up out of port A very heavilly, so there was some kind of internal problem.

Pulled the PM back out, (I'm good at it now), and stripped it down to look everything over. Didn't see anything obvious. All seals were in place and non damaged.

Now, with all that said I should add that during initial disassembly I had an issue with one of the snap rings inside the power piston assembly. The smaller of the two didn't retain all of its tension and fit pretty loosly when I reassembled. Did that have anything to do with my problem?? I don't know because it was still in place when I tore the system down the second time. Obviously something weird happened.

Put it all back together, went through the bench bleed again, hooked everything up, and re tested ports A and B and found no issues. Wish I could put a finger on what happened, but the system and brakes are working perfectly now, better than new!

Did you disassemble the power piston assembly by removing those two snap rings? Find anything out of the ordinary?
How did your Primary Piston assembly and Reaction assembly look?
C'mon guys, this is a Powermaster related thread. If the OP were interested in getting rid of it, I'm sure he wouldn't be putting so much effort into getting it up and working properly.
If you want to hype vacuum systems, please start your own thread.
Thanks TurboDave. I'll be honest in that I'm not completely opposed to converting, but after spending almost every night working on it for the passed two weeks my pride says I need to fix this.

Although what you're saying is certainly NOT what I wanted to hear, it is the advise that I've been looking for. I wondered if it was possibly and internal leak. I did take all the piston assemblies apart. I didn't really have any issues with the snap rings other than needing to do it alone with sub par snap ring pliers and no arbor press. It took me several tries.

Everything inside the powermaster looked really nice. I was told by the previous owner that it was a re-manufactured unit which I believe. The question is "By who?" Things looked pretty clean in there, but the check valve oring was destroyed and one of the springs was not put in the right spot. I cant remember the name of the spring because I don't have the Kirban book in front of me, but one of the long springs was in with the tiny tiny in the very bottom. I would think that should cause some serious issues, but the car actually braked fine like that. Regardless, I replaced all the orings that came with the Kirban kit, sanded the check valve surface with 1500 grit soaked in oil on top of a piece of glass, and reassembled in the correct order.

Now I'm here! It seems like the only difference between you and me is that I am not experiencing this big back flush that you speak of. Is that with the PM running? Which port (A or B) is closest to the firewall? Thanks again for the detailed response.
Just two more questions... Will the pressure coming out of the ports always be so obvious? When I place my finger over each one I don't really feel anything except for a little sucion from the pump supply port.

I think I know the answer to this, but would it be a bad idea to drive to BG like this from Indy? It stopped fine while driving around yesterday, but it seems to me that whatever is happening will get worse quickly if I have a bad seal.
I wouldn't drive it in its present condition.

You didn't disassemble the two larger parts with the large external springs did you??
I'm referring to these parts with the lip seals.


They only need cleaning, not disassembly.

Port A is closest to the firewall.

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What do you mean by "one of the long springs was in with the tiny tiny"?

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Correct. Those parts in the picture stayed in tact. I just cleaned them. If I had a picture on hand I would show you what I mean.
Here's a picture of the primary piston, reaction body, and secondary piston (top of photo).
The only requirements here is to pull the primary piston out of the reaction body, and pull out the reaction piston.


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Yikes... My primary piston doesn't look quite like that. It looks like the primary piston assembly is not supposed to come apart. My spring doesn't have any sort of retainer.

When I pulled mine apart the primary spring was where the secondary piston spring goes ALONG WITH the secondary piston spring, so the primary piston didn't have a spring at all. I put the spring back in the correct spot, but I guess it's still not going to be right unless I pull the PM apart again and replace the primary piston with a good one from another unit.

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