Pretty sure I know the answer to this, we've all been there, but a friend is asking and I want to make sure with my answer. Provided you can provide the pedal pressure, you can stop a car with a brake booster just as quickly with a loss of vacuum (engine dies etc.). Correct?
If you have a check valve in the vacuum line to the booster you should get 1-2 pedal applications with power assist. After that the pedal will be hard and require a fat foot to push it down, car will still stop, albeit with increased pedal effort.
Thanks guys. A bit more to the story: He's installed a PCV valve kit on his '57 Chev, replacing the road draft tube. Didn't want to pull the manifold and drill it, couldn't find a spacer plate for a 4GC, so T'd into the brake booster port, on the assumption that under braking manifold vacuum is high. Wants to test it and if it works leave it, otherwise drill a hole.
I would think as long as there is a check valve inline it should be ok. with the pcv valve inline I would also put a charcoal filter in there to keep contaminants out of the booster. the little black buggers gm used in the 70’s and 80’s
NOT...so correct..! IF...the correct parts are used...NO MORE pedal effort is required, with OR without a big ol booster. The four wheel disk (all Wilwood parts) on one of my cars (soon to be two) takes no more than two toes for a normal stop ! Just read up on using the correct parts and save the firewall from that nasty ol booster. Mike P.s. - Been discussed here many times. The search function will show the way.
Can you stop a vacuum assist as well when there is a loss of vacuum? As quickly? Maybe not. Can you stop it? Yes. It just requires more effort. I’ve had a booster go out. It stopped. But when your expecting an ezy pedal effort to stop and it’s not there, it takes more to stop it. Most of the performance rides I’ve worked on didn’t have power brakes. When the components match, a booster isn’t needed.
I'm mechanically inclined but Don't know all the dynamics in Car Science but I experienced this loss. It sucked but that's just one of the worries and to a new driver I guess the rule would be what I glean here today as it's been a while and it could happen anytime...I remember like power steering, power brakes require more Foot and Arm to achieve a proper stop or turn or All systems are important...Hotrod/Custom or Daily
actually this is not so correct…he was asking about a system with a booster. As in a loss of power assist. It will absolutely take more effort to stop. I believe you mean a system designed to not have a booster… then yes it absolutely can stop as well.
Ha...I misread, you are correct. And in my case, an 84, Chevelle wagon, an unmodified car... The one way vacuum valve popped (failed) during a sudden stop on the freeway. It took both feet and I was still very lucky that there was a large, non guard railed area of the freeway where I was able to go off into the dirt to finish my hard stop when traffic came to a sudden stop. I used my emergency brake to get home. THAT...was a chore..! Mike
One of the nice things about a Bendix vacuum assisted brake booster mounted on the inner fender panels of 50’s cars was the loss of vacuum didn’t change the stopping from using the normal non power pedal much. You could also pump the brakes which was near impossible with some of the systems used on bigger cars of the era.
Wrench97, have you been drinking?? What the hell are you talking about? Do you not understand the basics?
I think he may be referring to teeing it off the PVC which generally OEMs run to the valve cover. Or not, it is the 4th and celebrations are occurring.
Apparently he was either drinking or did not digest my gallery/link..we used to call that " jumping to conclusions"
It’s all good. More than likely even teed to the PVC line, wouldn’t pull anything into the booster as it dead heads there. But I guess some could makes it way. Sometimes it’s best not to try and better factory setups, they work pretty well when maintained. Now if retro fitting you’re on your own. Oh, usually get two “normal” stops when being towed and (obviously) engine off. Then it’s work.
I think it is dependent on the type of power brakes and the size of the vehicle. Here is my personal experience. I used to have a '48 Seagrave pumper with the Pierce-sourced V12 engine. It was not a small vehicle. It had some kind of power brakes, but I do not know what kind. When I purchased the truck it had 2300 road miles and everything was in excellent shape (except for the gas gauge, which was right most of the time, but would fail periodically). I was on my way to a fire muster one fine Saturday when I unexpectedly ran out of gas, and the engine quit. Like "Mike VV" above, I experienced a dramatic loss of braking power. I literally had no brakes. Like him, I ended up standing on the brake pedal with both feet. It had almost no effect. I also was lucky to have lot of space and coasted into a large empty parking lot and was able to scrub off enough speed to get it stopped when I ran it into a curb. I weighed 235 in those days and was quite a bit younger, but standing on the brakes and pulling up on the steering wheel had almost no effect. In case someone thinks it was some other component that failed, putting 10 gallons of gas in the tank and re-starting the engine brought the brakes back all the way. I was always extremely careful after that and checked the gas level with a stick in the tank and made sure the fuel pumps were always in good shape. I shudder when I think what might have happened if I had not had a ton of room to get that beast stopped.
@tubman you may have had a hydro vac. I had one years ago from a 1.5 ton That stopped well. I recall the 216 smoking bad and thought I lunched the engine. Seems it got some type of leak somewhere and pulled brake fluid into the engine. Well, at least that’s what they told me and charged me (well my dad) 40 bucks to pull and bypass it Had to get that hay hauled!
Power brake have less mechanical advantage than non power brakes ( 5 to 1 for power and like 6 to 1 for non power) so yes it will be harder to stop.
Have you never seen a PCV hose fail because of oil in it? If not you would be the one that has no idea how the system works. When the car is running the vacuum pulls the crankcase blow by some oil included into the intake manifold which leaves traces of oil in the line, if you tee it to the booster, when you turn the engine off the booster holds vacuum via a check valve any leakage it will suck the trace amounts of oil from the hose, anytime it backfires you now have pressure pushing the air and trace oil into the booster. Oil in the booster causes the diaphragm to fail not in short period of time but over months of running and sitting it can happen, a separate hose from the intake eliminates any trace oil, so have at just don't drive behind me.
Ok, Mr. Wrench, One more time. What makes you think that ANY of the hose fittings or the discharge of the vacuum pump ties into a PCV circuit? If you paid any attention, you would NOTICE that the only connection of the hoses to ANYTHING OTHER than the vacuum tank, pressure switch, booster, or anything else under the hood is a spare port on the carb for the discharge of the vacuum pump/check valves. Actually it's pretty simple, and I have no idea how/where you got the idea that "OIL" is involved anywhere in the system. Soooooo.. pay attention...
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