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Technical Can Brakes be Powered by a Vacuum Pump only?

Discussion in 'Traditional Hot Rods' started by Wavetrain75, Jan 8, 2022.

  1. Wavetrain75
    Joined: Jan 22, 2020
    Posts: 31


    Or are the pumps used as a booster for manifold air?

    I have a stock flathead V8 in an F-1 truck with power brakes. It's possible I have a vacuum leak and was thinking that eliminating all the unnecessary vacuum lines is one way to minimize them in the future. Not using vacuum wipers, just the distributor advance and the brakes.
  2. anthony myrick
    Joined: Sep 4, 2009
    Posts: 10,053

    anthony myrick

    The engine is a vacuum/air pump.
    So yes.
    But if you have a vacuum leak and it’s in the breaking system then it’s more than likely at the booster.
    A vacuum boaster is a simple system. Adding a pump not due to a performance cam sounds like an unnecessary solution
    You can block it off and see if anything changes.
    If you run a vacuum pump, how is it eliminating vacuum lines?
    The booster still connects to the pump.
    Last edited: Jan 9, 2022
  3. indyjps
    Joined: Feb 21, 2007
    Posts: 4,839


    You could just eliminate the power booster. Properly sized master cylinder with manual brakes works well.
    A lot of the aftermarket power brake "kits" aren't so great to begin with.
    hemihotrod66, mad mikey and 2OLD2FAST like this.
  4. PhilA
    Joined: Sep 6, 2018
    Posts: 1,427


    Edit- beaten to a few answers by the posts above, which arrived as I was typing!

    Yes, it is totally possible to run a vacuum booster off an engine-driven pump- that's how it's done on diesel engines because they have no throttle plate to cause a vacuum to be drawn in the manifold.
    However, the vacuum pump fitted to most 40's and 50's vehicles is inadequate to run a brake booster. It's only there to assist a vacuum wiper motor when there is no engine vacuum. Most don't have the capacity to solely run a brake booster.
    The brake booster should be tapped off before the pump, and should have a one-way valve to prevent any vacuum drawn from being bled away when the manifold gains pressure.

    So, no. If you have a vacuum leak in a simple system like that you need to check the booster and pump for leaks. My pump needed to be rebuilt, it had a split in the diaphragm that was causing the manifold to draw in through the crank case- quite a major leak but only enough to cause idle to be difficult to set mixture. A flathead will tolerate quite a bad leak before it won't run. It was also inaudible. I would suggest blocking off the pipes in stages starting at the manifold and working with a vacuum gauge to determine where you're losing vacuum.
    Overall, the system you have is simple- I would say negate the pipework through the pump and run direct manifold vacuum to the booster. If that fails, you at least know what is at fault (pipe, booster diaphragm). The engine itself is such an effective pump I wouldn't want to not use it as a vacuum source.


  5. Mimilan
    Joined: Jun 13, 2019
    Posts: 1,104


    Toyota Prius has an electric vacuum pump for the brakes.
    The pump starts up as soon as you open the driver's door. [that way you still have brakes when the car starts off in electric mode.

    Most small Japanese Diesel engines have a vacuum pump driven from the Alternator.
    These things pull a decent vacuum and would probably cure the dead wiper issues when accelerating up a hill.

    Here's a Toyota alternator
    Last edited: Jan 9, 2022
    jimmy six, VANDENPLAS, rod1 and 2 others like this.
  6. finn
    Joined: Jan 25, 2006
    Posts: 981


    He mid eighties to nineties Ford IDI Diesels all had a belt driven vacuum pump.

    Over a million were produced.
  7. Reidy
    Joined: May 13, 2016
    Posts: 199


    If you were to do that I would recommend using similar thinking to truck air brakes. In this this situation you would have it so with no vacuum the brakes are on. When the engine is running the vacuum would release the brakes. When you ally the brake pedal a valve would open to dump vacuum and let the brakes apply.

    This makes it fail safe if the engine stalls or you lose a vacuum line.

  8. Mr48chev
    Joined: Dec 28, 2007
    Posts: 30,845


    There are plenty of beer driven and electric vacuum pumps out there designed specifically for brakes. There are some aftermarket oem design units on Amazon for around 100 $ but at least with electric you should be able to find a good used one.
    VANDENPLAS likes this.
  9. F-ONE
    Joined: Mar 27, 2008
    Posts: 3,092

    from Alabama

    Are these stock power brakes? I'm not aware of F-1s having power brakes. The big trucks could have a brake aid but you get into some strange and rare stuff, at least for the average hot-rodder.

    If aftermarket, the flathead V8 may not have the vacuum signal to run that booster. It's a 100 HP engine. It could run the wipers but even wipers of the period were offered as an option to run off a special fuel pump.
    It's asking a Lot of that little 94 to run a big brake booster.

    Vaccum pump? Are you kidding?
    How in the world can a Powerstroke Vacuum pump be mounted on a 8RT Flathead? There may be something out there but...
    The easiest solution is good non power brakes.
    If you must run power brakes, the vacuum cylinder used needs to be matched to the requirements of the Flathead.
  10. MojoRacing
    Joined: Mar 24, 2013
    Posts: 59


    My 91 f350 7.3 had this they are fairly small and compact, rock auto has them reasonably priced.
    Truckdoctor Andy likes this.
  11. bschwoeble
    Joined: Oct 20, 2008
    Posts: 775


    Because of the cam in my "340" powered coupe, I use an aftermarket pump. I got mine from "Right Stuff" almost 7 yrs. ago. I will say, it's a bit noisy when running.
    Lloyd's paint & glass likes this.
  12. blowby
    Joined: Dec 27, 2012
    Posts: 8,306

    from Nicasio Ca

    That's how I power mine. :)
  13. squirrel
    Joined: Sep 23, 2004
    Posts: 50,931


    this spell check fix is so good that it beers repeating.....
  14. belair
    Joined: Jul 10, 2006
    Posts: 8,864


    I can't beer this anymore.
  15. blowby
    Joined: Dec 27, 2012
    Posts: 8,306

    from Nicasio Ca

    It's the schlitz when that happens.
  16. hotrodjack33
    Joined: Aug 19, 2019
    Posts: 3,485


    I had beer in my vacuum lines once...the idle "hops" around and it would "barley" run:(.
  17. nosford
    Joined: Feb 7, 2011
    Posts: 680


    Junkyard shopping option, all Chrysler, Dodge, Jeep, and Ram trucks with the 3.6L V6 (and 3.2L Jeep Cherokee) have an electric Vacuum pump for the brake booster. It is used in conjunction with the engine provided vacuum and a couple of check valves in line to keep the vacuum where it is supposed to be. They have built over 3 million of these V6 engines so should be plenty out there in Junkyards.
  18. No, you're gonna need a brake pedal and a master cylinder :D like stated up there, the 12v units are loud. I'm in the camp that if you have low vacuum due to a big cam, just go manual brakes. I like beer
  19. I agree with the manual brakes. If you are trying to simplify things then that’s the way to do it. I have manual breaks on my truck and it stops just fine, I don’t feel the need to go to the hassle of making them power. I did put power steering in it, mostly because I’m lazy.

    Oh, I like beer as well.
    hotrodjack33 likes this.
  20. CME1
    Joined: Aug 10, 2010
    Posts: 231


    I too like beer, but not in me brake system!:rolleyes:
    blowby and hotrodjack33 like this.
  21. geoford41
    Joined: Jul 26, 2011
    Posts: 634

    from Delaware

    I am in the process right now of switching out a TH350 to a 200-4R trans and had to move the radius rod ends out tom the X member where I had interference with the dual Vacuum brake booster, I am waiting for a Hydro booster that should take care of the problem and give me a bunch more hydraulic pressure off the PS pump. It is claimed much better braking with this and no more Vacuum problems.

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