Supplemental Brake Assist

Real tech discussion on design, fabrication, testing, development of custom or adapted parts for Pontiac Fieros. Not questions about the power a CAI will give.

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ericjon262
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Supplemental Brake Assist

Post by ericjon262 »

some GM trucks have a system called Supplemental Brake Assist (SBA), the system is a simple vacuum pump that bolts to the brake booster and draws a vacuum on the booster, the discharge of the pump goes back to the engine vac source, thus, acting as a supplement and not a primary source, but I was thinking, maybe it would work as a primary source. the pump is about the size of a 16 oz energy drink can

Diagram:
booster.jpg
booster.jpg (80.33 KiB) Viewed 667 times
what I know so far:
-not PCM controlled, there is a VSS input from the instrument cluster.
-it has an internal pressure switch (unsure of set points).
-it determines the engine is running based on a signal from the generator.
-factory fuse for the motor is 15 amp.

unknowns:
-duty cycle limitations.
-flow rate, can it handle running a booster by itself.
-can it be made to run without instrument cluster and/or VSS/generator signals

any thoughts on running one of these? I like the idea of eliminating a potential boost leak that runs the length of the car, and still having power brakes.
"I am not what you so glibly call to be a civilized man. I have broken with society for reasons which I alone am able to appreciate. I am therefore not subject to it's stupid laws, and I ask you to never allude to them in my presence again."
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Shaun41178(2)
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Re: Supplemental Brake Assist

Post by Shaun41178(2) »

You shouldn't have a boost leak the length of the car because gm installed a 1 way check valve in the brake booster line. Its on the firewall.

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The Dark Side of Will
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Re: Supplemental Brake Assist

Post by The Dark Side of Will »

SOME manufacturers (Mercedes? Ford?) had some diesel applications in which they used a vacuum pump as the primary vacuum source for power brakes. You're better off with one of those, as it's designed with that safety/reliability requirement in mind.

When a heavy truck is climbing a steep mountain (eg, WOT in 3rd gear for an extended period of time), and the driver has to get on the brakes suddenly, he could experience an unboosted pedal for maybe as much as a second until MAP drops and the engine pulls a vacuum on the booster. This pump is only designed to take that edge off the system.

The Fiero booster tube is steel, and if you have a vac leak in/around your booster, you should fix it. I think You're considering adding a more complex and less reliable system to replace a simple, reliable (and lightweight!) system...

And as Shaun said, there's a check valve in the system. You could also add a vacuum accumulator to increase the amount of time you can run in boost before you have to "recharge" the booster from the manifold.
ericjon262
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Re: Supplemental Brake Assist

Post by ericjon262 »

I don't think the firewall mounted valve is still in place on my car, but it is easy to install a new one. I wasn't necessarily thinking about installing this on my car, more just thinking out loud, as it may offer some improvement in booster performance under rapid use, in car with an engine that doesn't produce a high vacuum.
"I am not what you so glibly call to be a civilized man. I have broken with society for reasons which I alone am able to appreciate. I am therefore not subject to it's stupid laws, and I ask you to never allude to them in my presence again."
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Re: Supplemental Brake Assist

Post by The Dark Side of Will »

US Domestic hyrdoboosts (should be hyrdauboost, but 'tev) are big, used in trucks, made of iron and heavy.

However, BMW and presumably other Euro marques use ZF hydroboosts that are compact, used in cars, made of aluminum and lightweight. The E23/E24 units have divorced accumulators and are actually extremely easy to package. They come in very handy when doing V8 swaps on older BMW's, as the diameter of a vacuum booster makes it interfere with the left valve cover.

They're still not as light as a vacuum booster, but if the car already has power steering, they are a good alternative that doesn't add much weight and makes the brakes independent of engine vacuum.

You *could* use an electric vacuum pump as long as you had a vacuum reservoir that would allow you to stop the car if the pump failed. Vacuum reservoirs can only be so dense, and thus tend to be bulky, but at least they're light weight. Hyrdoboosts have accumulators for that reason... they give you enough boost to stop the vehicle if you toss the power steering belt.
ericjon262
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Re: Supplemental Brake Assist

Post by ericjon262 »

the BMW unit is pretty small. if I was more intent on installing power steering on this car, I would look into that instead of a GM booster.
"I am not what you so glibly call to be a civilized man. I have broken with society for reasons which I alone am able to appreciate. I am therefore not subject to it's stupid laws, and I ask you to never allude to them in my presence again."
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