91GTP powermaster III problems no fluid to back brakes

[m0sh_man]

Ive tried two powermaster 3 units, the entire mastercylinder assembly with actuator and everything, both ahve the exact same problem, front brakes bleed just fine, but if you try to bleed the rear, NOTHING happens.

 

the manual says to do this all with the key off, so the electric pumps in the mastercylinder are NOT engaged. so i done that, like stated NOTHING comes out of the rear calipers, both mastercylinders done the SAME THING.

 

so i figured what the hell, ill try with the key ON, turned it on and pressed the brake, and fluid pours from the calipers, like a constant pump (out the bleeder valve)

 

so does anyone have any clues why it WONT let me bleed without the pump being energized?

 

im at wits end on this car, im VERY pissed off, ive owned it for nearly two years now, and ive never driven it, runs/drives great too, and its the rare 5 speed.....

 

someone help, please any suggestions.

 

matthew

[LukeZ34]

Have you checked the rear proportioning valve? It's right in front of the fuel tank, next to the fuel filter.

They are known to leak, but in your case, it could be completely plugged up or something.

Since there is only 1 brake line going to the rear, the proportioning valve splits it in to 2.

[m0sh_man]

is it a true proportioning valve? or just a Y link?

 

why would it shoot fluid out when the key is on then?

 

matthew

[m0sh_man]

someone has to have more information on the PMIII brake system.

 

matthew

[WhiteOut]

Give me a day or so to research it (I'm at work right now). I've got a shop manual for the 90' Trofeo I used to have. It should have said info.

 

I can tell you though that when I bled my brakes on the Trofeo I always had to have the car in the ACC position otherwise the pump won't run and you'll eventually run out of pressure untill the system recharges (about 20-25 pumps of the pedal).

[bryanjoseph]

check out this site: http://www.tpsgarage.com/

 

It has some great info on the Powermaster III.

 

It says to bleed all four calipers with the ignition on. My manual(Chilton's) says to bleed the rears with the ignition on. My w-body also will not bleed at the rears without the ignition on. Bleeding with the ignition on worked just fine. The rear brakes work properly. Bleedding the fronts this way as well saves time. I'm not exactly sure why the rears don't bleed without power. Perhaps the solenoids(for ABS control in the Powermaster III) for the rears close when the ignition is off so all braking power would be saved for the fronts in case the engine stalls. That is only a guess, though.

[R Dubya]

Only 89s and 90s got that proportioning valve.. I would start at the MC. How does the fluid look? Possible blockage in the lines?

[no1kicker]

so does anyone have any clues why it WONT let me bleed without the pump being energized?

 

I hope I'm not missing the obvious here. I would think you need the pump to be on to bleed the brakes. In the manual it says to pump the brake pedal 40 times with the key off to relieve system pressure. So without the key in the on position, and the pump running, there is nothing keeping the system pressurized. The accumulator provides pressure, but the pump is constantly running in these cars every few pedal presses to keep pressure constant.

 

So unless I'm missing the big picture, if fluid comes out when the pump is running, I don't see a big problem.

[WhiteOut]

Sorry, the Trofeo book couldn't come through for me. Its got two lines running to the rear of the car, not one, so I can't help with any proportioning valve issues.