brake help

[williambavila]

Hey guys i have the infamous power master brake system in my car right now. I have just replaced the accumulator bowl and switch on the set up because the motor would just keep running. Now i have a super hard pedal and a light that stays on all the time. the hard pedal is intermitant but the light will usually come on after hitting brake pedal 15+ times. what in the world is wrong. I am thinking of switching to the vacuume brake setup but i still want to know what this could be.

 

[1quick6]

You might want to check out this thread before you do anything drastic. Unfortunately, if you have bought a new switch and accumulator, you are nearing the price of a complete conversion.

What is your PM motor doing? Does it sound like it is charging up the accumulator?

 

[Red Regal T]

Sounds like the master cylinder is bad. Change over to something else. End your headaches.

 

[williambavila]

Sounds like the master cylinder is bad. Change over to something else. End your headaches.

vacuume?? is that what you mean?:biggrin::biggrin::biggrin:

 

[1quick6]

Vacuum or hydroboost. You'll have everything new except the motor by the time you fix the PM. Just when you think you're good to go, the motor will go. That's how things in the Buick world work.

I'd have to agree that your mc sounds suspect. There's an internal leak somewhere.

 

[Tommy]

Hi there,

you sound very knowlegdeable about the buick power master brake system. can you educate me in how the brak accumulator bowl works? I recently ordered one from Kirban and I couldn't believe how heavy this item was. When I get around to installing it do I need to coat the brake bowl threads with a sealant or do I simply install it dry with the supplied o ring.

Thanks for any information

Tommy

 

[1quick6]

I just know enough to be dangerous on the PM systems.

Basically, the accumulator stores pressure supplied by the electric motor to assist with braking. They are heavy because it is a thick housing to be able to stand up to the pressure, hence the warnings to depressurize the system before servicing. When they start to fail, they will bleed off pressure requiring the electric motor to run more to keep the pressure up. When you replace yours, pump the pedal 15 times to depressurize and then just remove and replace.

 

[POWERBRAKEBOB]

accumulator

That accumulator is heavy welded steel with a rolling diaphragm in it. The Powermaster uses the 12v pump, switch, and accum. to build up approx 2600psi into the accum. At that pressure, the switch opens and stops the motor. The high pressure against the vanes of the pump, which is pumping brake fluid, the plastic switch, and the accum. is high stress against those components. The vanes in the pump are phenolic, which wears out quickly. Brake fluid is not an oil, and does not lubricate the pump vanes. The pump pumps up the accum to the high pressure, and then holds it. When you apply the brake pedal, some of that "accumulated" pressure is used to push the power piston in the booster/master. When the pressure is used down to approx 1200psi, the switch tells the motor to pump up again. Lincoln LSC's, Buick Reattas, Rolls Royce, Citroens, and some Cherokees used the electric units. Almost all of those motors have worn out. Usually, since new units are hard to find, and the cars end up being scrapped. IF the cars are converted to another brake booster, such as the Hydroboost, the car can stay on the road. Few guys have the expertise to redesign the pedal ratio, master cyl size, and line connections to do this kind of work, so most of the cars end up being scrapped.