PMIII advantage??

[Lee]

Reading a previous post I got to thinking :shock: :shock: In a vacuum assisted brake system when the engine quits the brakes die off right? Work but very poor and hard?

 

Not tested yet but.....if the engine dies in a PMIII car, the power is still on and the motor would still be on....ergo the brakes should still work as if everything were running right?

 

I knew there had to be something good about this bi@$ch.

[White93z34]

go out and kill the car while driving and tell us.

[94CutlassSLCoupe]

well...you may be right but its not like these cars should stall very often (I mean shit, they are almost all automatics) and well I have a car with MANUAL (no assist) brakes on it and it stops fine...actually its an excellent stopping car.

[Prospeeder]

Reading a previous post I got to thinking :shock: :shock: In a vacuum assisted brake system when the engine quits the brakes die off right? Work but very poor and hard?

 

Not tested yet but.....if the engine dies in a PMIII car, the power is still on and the motor would still be on....ergo the brakes should still work as if everything were running right?

 

I knew there had to be something good about this bi@$ch.

 

Werd Yo, Da Powa masta III is da shit! Yes it still supplies full braking power and booster and antilock without the engine running. I dont mind mine, it stopped this big ass car great

[Turbo231]

True...but if you consider that most brake systems have enough vacuum in the system to stop you at least once, if not twice...lack of power steering is more of a problem then anything...but you don't see me converting to an electric power steering pump.

[Prospeeder]

i belive it was a thing with the turbo boost, when under boost, all the vacuum lines are under pressure, so if your boosting, and suddenly brake, im guessing there would be horrid brakes and a solid pedal from the possitive pressure in the vacuum system, And mabye the extra boost would ruin the brake booster with the vacuum setup, and youd have to have one big ass check valve to fix that tho, mabye just a thought, i have no idea if any of this really could happen

[Guest TurboSedan]

i belive it was a thing with the turbo boost, when under boost, all the vacuum lines are under pressure, so if your boosting, and suddenly brake, im guessing there would be horrid brakes and a solid pedal from the possitive pressure in the vacuum system, And mabye the extra boost would ruin the brake booster with the vacuum setup, and youd have to have one big ass check valve to fix that tho, mabye just a thought, i have no idea if any of this really could happen

 

there is a check valve there for that. it's not a big ass check valve my Cutlass has it (stock), which doesn't have PMIII and wasn't turbocharged to begin with. my turbocharging the car had no direct effects on the brake system.

[Crazy K]

there is a check valve there for that. it's not a big ass check valve my Cutlass has it (stock), which doesn't have PMIII and wasn't turbocharged to begin with. my turbocharging the car had no direct effects on the brake system.

 

The check valve is the little L fitting between the hose and the booster on our cars. Once it gets a vacuum it holds a vacuum. On one car I had it felt like there wasn inconsistant/weak brake assist, it was due to dryrot of the check valve. one HELP brand part and I was ready to go.

 

In the event of a stall, the car should have one normal stop left, and a slightly weaker second stop, as vacuum decreases. I determined a check valve was bad back on the old buick mentioned above as turning off the engine immediately lost vacuum assist... The brakes were still adequate when the engien was on.

 

On cartalk, there was someone who crashed a car because the check valve was bad..... It was a new VW (maybe a 95 passat at the time?), he was facing uphill on a hill leading down to his garage, had his foot on the brake and shut the engine off... and the brake pedal went stiff and the car rolled backwards into the garage, through it's door and caught and folded the drivers door on the frame, which had been open at the time.....

 

 

moral of the story? check your check valve!

[Turbo231]

Very reminiscent of what GM did with their Turbo 3.8s...originally, prior to late 85, they used Hydra boost, which actually powered the brake booster from the power steering system. This system was also used on Diesels thanks to their low vacuum. Then in super late 85 to 86-87 model years, the Turbos used the PM1 system, which was an electric pump and Nitrogen reservoir. For some reason, this was also used on some larger gas powered Buick wagons. The idea again was the when the Turbo was running, there would be insufficient vacuum to run the brake system safely. That being said and as previously mentioned in these posts, actual "boost" times were low and that a check valve could be installed and a vacuum system retained, as shown my GM not installing the PowerMaster brake system on the 1989 Turbo TA, but instead just installing a check valve in the line to the brake booster.