GM Powermaster brake installation

[CobraV8]

I was searching for a manual brake master cylinder for my Cobra (as a vacum booster will interfere with steering and headers) and ended up buying a GM powermaster unit on ebay for 66 bucks. That's what it looks like:



Before I had never even heard about an electric brake booster but when I saw this thing it seemed to me like it'll solve a lot of problems if I put it in my Cobra.

I thought I was the first person to ever do this but now I'm happy to see some of you guys have one in their Cobras as well and this conversion is not uncommon (esp. on FFR cars). So this should work quite well for my Cobra too!

All I have is what's shown in the picture. This means I have the brake master cylinder, electric pump, accumulator, fluid reservoir and lines, so the unit is pretty complete. What I'm missing is the wiring harness and controller. What stuff do I need and how does the system work at all?
I assume pressure is built up in the accumulator by the pump until the switch tells the pump to stop when pressure is high enough. Is there some kind of controller between the switch and pump or is it simply wired via some kind of relay? Do I need to use original GM parts or can I fabricate a custom wiring harness?

What wire has to be connected to what pin? Where do the ground wire and the 12 Volt current supply go?

As you can see the electrical installation of the unit is the most challenging part for me as I have practically no information yet.

Another consideration is if I can use the Ford actuating rod, but I think this should be no problem as long as it fits in the hole of the cylinder but isn't too loose on the other hand.

I hope someone who has done this installation before can help me!

Thanks,

Simon

[TonyMadrid]

What did it come out of? I think that's the question that need asking.

After we resolve that then we can properly evaluate.

But I'm interested.

Tony

[BT SNAKE]

Simon & Tony,
Go to John Spina's web site at Casper Electronics and ask John for the harness he makes up for this application. He really does a nice job with factory connectors and all.
http://www.casperselectronics.com/

Tell him Hersh says hi!
John can also give you some installation tips too as he has this system on his Everett Morrison Cobra.

Hersh

[DavidWard]

Contact John Spina at caspers@wwa.com for a wiring harness. He has one that is plug 'n play - simply hook up a +12V wire and a ground and everything else plugs in. The electronics are built into the motor. The motor is controlled by the pressure switch, which is mounted directly on top of the cylinder near the firewall. You will probably have to round up some brake line fittings. I found what I needed at a local hydraulics shop, but some people have found them at NAPA. If it's any help, they are the same fittings that fit a '84 Mustang manual master cylinder. I also used a push rod from a Mustang, cut down to the correct length.

The motor can be remotely mounted if necessary. Just make sure the motor does not contact ground. If so, the motor will run continuously and burn itself out.

Several of us are running this set-up on FFR cars. I have almost 30,000 miles on mine, and the only problem I've had is I had to replace the pressure switch once. By the way, parts are rediculously expensive for this unit. Cheapest I found the pressure switch was $160.

David

[ff2_emtb]

Jeez, I can't believe guys are still buying this junk thing. These were used on Buick Grand Nationals and I believe big Buick station wagons. The major problems with these are the accumulator (big black ball looking thing) and the switches going bad. A lot of GN guys have switched from these to vacuum brakes because of these problems. If you ever need help on these, go to www.gnttype.org and look under the technical items. There is a lot of info there on diagnosis and repair on these.

t

[CobraV8]

Excellent!!! I just love this site, thanks guys!!!

That's all I need to know to install the powermaster into my Cobra.

I will order the powermaster harness from Casper Electronics, this piece and the brake line fittings is everything I'm missing. I already have an adjustable Wilwood proportioning valve for the rear brakes installed and I will modify the Mustang brake pushrod for the correct length.

I know parts are not cheap, and the electric pump may not be as realiable as a vacuum booster but this is the only way to add power brakes to my Cobra. I've tried it with several boosters and they all were way too big to ever fit between the headers and steering column of my Cobra.

Overall I think the powermaster system is the best solution.

Thanks again for helping,

Simon

[ENTDOC]

I will just throw this in in case the PM does not workout.A Masterpower brakes 7 inch dual diaphragm booster may be small enough for your application.It will handle 4 wheel disc and can be found on ebay with mastercylinder for 139.00(look under street rod master cylinder) chuck

[niles]

CobraV8'
I installed a new GM in my cobra. It was a PITA; the motor will hit the pipes; had to relocate and replumb the whole thing. The good parts is the brakes work great; low pedal pressure and can lock them up easily. The bad part is the motor had to be located on the tranie tunnel over the top on the trannie; the MC must be above the motor so the fluid can flow down hill to the pump. If I have a problem with the elec. motor I;ll hve to remove engine to get to it. If I had to do it again; I'd go vaccum. All the SPF are using vac and many have hi-power low vac motors and they are working OK. Just might take a few revs to get some vac stored up

gn