Powermaster Rebuild

[bryes]

Hello everybody.


I still have a couple of nagging issues that have prevented me from driving my GN much after getting the motor back together. The major one right now is the  powermaster. Unfortunately I don't have any bars of gold laying around to trade for a rebuilt one, and the used one that I bought as a "known good" unit turned out to be a core; so I'm left now with trying to rebuild it myself.


Fortunately, since completing the engine a year ago (or was it two?) there has been an empty space in my living room just begging to be filled again with buick parts. And with temperatures approaching the century mark here in Savannah, I have a some spare indoor time on my hands right now. So I took this time to tear apart the core that I have and I'd like to get it to a point that I just have to just swap it in, bleed the system and go.


I have labeled my PM parts below similar to the one in http://www.gnttype.org/techarea/brakes/powermaster.jpg. I have measured the o-rings and seals with calipers and matched them to standard sizes as well as I can, and they are summarized in the picture. Since nobody makes a rebuild kit anymore, it looks like I am going to have to get all o-rings and seals from a hydraulics place. In researching it, i have found that  EDPM or Silicone are the two options that are compatible with brake fluid, and it seems that EDPM is superior.

I'm just looking for advice for those who have been down this road before. Maybe i'm just a glutten for punishment trying restore a PM (and not convert), but I'd at least like to get a good PM MC in the car to decide if 1 of the 2 accumulators I have em "accumulated" is good. I think that the seals will not cost very much, so all I have to lose is my time... and that is not worth anything


Finally, it looks like somebody cut the end off of the power piston spool (#46) in my core with a hacksaw. Does anyone have a power piston assembly laying around (#25) they wouldn't mind parting with? I think Autozone was out of stock! If I had to, I can hopefully use the assembly that is in my car right now, but I'd rather not.

[Just a Six?]

So you purchased a "known Good" core that had a hacksaw taken to it! I would be asking for some or all of my $$ back unless you got it very cheap? Good luck with it & I understand you "like me" enjoy tearing stuff apart & learning but with Brakes being a rather important part of a car I would just convert to Vacuum. Either way good luck with your project!     

[TexasT]

I'm gonna have to agree with your assesment that you are a glutten for punishment.

After you get the thing working. You can have a failure and learn front sheet metal replacement.

[bryes]

I wish I had seen that hacked part in the MC before, but I bought it probably a year ago and have since swapped several parts from it onto my existing unit. I paid 75-100 bucks for it I think, so maybe I still got my money's worth anyway?? I have no idea what the idea of cutting it was, could they not separate it from the brake rod??


I know that a person takes on a larger risk using a PM than the other systems, so that's why I am trying to rebuild this MC while the one in my car works and the brake light doesn't come on. With the one in the car the fluid won't stay clear and I believe it has an internal leak, so before I drive it I'd like to have a system where there are no known faults. Then I'll be diligent and not take any chances to avoid sheet metal repair should the brake light rear it's ugly head again!


In the end I'll still have a system with a quarter century old pump, so I'll be keeping my eye out for a vacuum or hydroboost while I figure out what I ultimately want to do.

[TexasT]

I had that system when the car was pretty new(about 30k miles)  and it quit on me then. Never trusted it after that.

[daveismissing]

Internal leak?  cycles frequently?
If you have an iron prop valve fluid probably get dirtier quicker?

[bryes]

The pump comes on I think every time I step on the brakes, and the fluid level of the rear brake reservoir increases while the passenger side of the reservoir decreases after cycling the brakes. I put new fluid in the PM, and it became opaque very quickly. I think it's probably picking up stuff from the PM MC rather than the proportioning valve. I don't think that fluid would become contaminated very quickly if it were from the PV.