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I met a guy yesterday with a 327 C2 and a dual master cylinder power booster brake system. He had the vacuum connected to the ported vacuum of his carb (no vacuum at idle). He claimed he had oil sucked out of the master cylinder every time he did a fast release of the throttle pedal from high rpm without clutching (causing high vacuum) when the booster was connected to the intake manifold.
Does this make sense?
I met a guy yesterday with a 327 C2 and a dual master cylinder power booster brake system. He had the vacuum connected to the ported vacuum of his carb (no vacuum at idle). He claimed he had oil sucked out of the master cylinder every time he did a fast release of the throttle pedal from high rpm without clutching (causing high vacuum) when the booster was connected to the intake manifold.
Does this make sense?
No.
There is no "oil"(?) in the master cylinder. The vacuum is not connected to the brake fluid in any way.
The P/B booster line is normally 3/8" hose and the 'ported' line is normally 3/16" line, how did he connect the two?
So he had no power brakes until the throttle was openned enough to create vacuum, so when he released the throttle to brake he had no power brakes!
Joe
He prob meant he was getting engine oil 'pullover' from the intake manifold into the rubber hose going to the power brake booster (not master cylinder) on deceleration. That may be due to engine modifications. If he thought it was oil out of the master cylinder he is clueless and anything he says should be ignored.
Understand what plaidside (Joe) said above.
If hooked up as this guy says...the car could be speeding up on an emergency stop and the owner's foot comes off the gas (closing the carb's throttle plates and forcing ported vacuum to zero) and his foot then goes onto the now "unboosted" brake pedal to try to bring the car to a stop.
Power boosted brakes have a 'reserve' charge to support a few pedal pumps without active vacuum but that would be one dangerous-*** way to drive...
If you have power brakes and you want to simulate this - start your car up and pump the brakes a few times, take your foot off the brake pedal, and, turn off the engine. Now - pump the brake pedal and you'll find you get 2-3 'boosted' pumps until the pedal goes hard as the reserve is depleted.
You wanna run around like that on the highway ?
Last edited by Frankie the Fink; 05-23-2016 at 08:15 AM.
Did you actually see the guys car? Or did he just say he had one.
I saw the car, and I saw how he had hooked it up too. Now, I am not an experienced car mechanic, he said he was. I always want to learn...
The only reason I started this tread was to see if there was any logic to it, a logic that I could not see . Now it seems there is none except a dangerous one as Frankie and Joe describe above...
Last edited by alexandervdr; 05-23-2016 at 12:42 PM.
My power brakes do not run off of the carburetor. They operate off of manifold vacuum not ported carb vacuum. Here are two photos showing my setup.
Vacuum taken off a carb's base (below the throttle plates) IS full manifold vacuum just as a connection directly to the intake. Vacuum taken off a carb above the throttle plates is 'ported'; e.g. vacuum is effectively cut off when the throttle plates close or at idle...
Vacuum taken off a carb's base (below the throttle plates) IS full manifold vacuum just as a connection directly to the intake. Vacuum taken off a carb above the throttle plates is 'ported'; e.g. vacuum is effectively cut off when the throttle plates close or at idle...
Vacuum taken off a carb's base (below the throttle plates) IS full manifold vacuum just as a connection directly to the intake. Vacuum taken off a carb above the throttle plates is 'ported'; e.g. vacuum is effectively cut off when the throttle plates close or at idle...
Even with the original intake manifold it came off of it, rather than the carb. From what I can remember on the original carb there wasn't a rear provision in the base for a vacuum hookup. Could be wrong though on that. Memory is good just short.
My point is that it doesn't matter if the vacuum is taken off the carb base or intake; if its below the throttle plates its full vacuum. Your car may be correct or not but its using full vacuum as it should.
It is impossible for oil to enter the brake booster as the Full Vacuum line connects to it is a one way check valve that will prevent any oil getting into the booster.
It is impossible for oil to enter the brake booster as the Full Vacuum line connects to it is a one way check valve that will prevent any oil getting into the booster.
Four engine oil to get into the booster would require a combination of a bad check valve on the booster and excessive blow by from the crankcase.
For the master cylinder to be sucked dry of brake fluid, would mean a bad master cylinder leaking through a bad or missing seal on the back of the master cylinder. I have had master cylinders leaking from the back.
Ported vacuum is a NO NO as said.
05-23-2016, 07:19 AM
ported vacuum for power brake booster?
