hydro- boost brake using g-m astro unit

Brakes for your Classic Mopar

  1. 22dog22

    22dog22 Well-Known Member

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    has any one used a used gm astro van hydro boost brake unit in an a body cuda ??, seems you can get a good used unit for cheap as compared to a new aftermarket unit. was it hard to hook up to the power steering pump ?
     
  2. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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  3. brian6pac

    brian6pac Well-Known Member

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    I have used them before, not on a A-Body but they do work great.
     
  4. dodgedifferent2

    dodgedifferent2 Well-Known Member

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    I used one from a diesel ram truck. The reservoir was smaller and cleared valve covers better.

    Had a bit of an issue with pedal return. Needed a heavier internal spring on the pushrod but could not find one so I added an external spring to bring the pedal back and it worked like a charm.
    I am using a 15/16 bore dakota/jeep master cylinder. I used a thinner clocking plate as the rams was a half inch thick. I had to create a longer pushrod between master cylinder and hydroboost.

    I used the rams mounting plate but drilled new holes in the plate to adapt to my darts pattern.
     
    Last edited: Aug 4, 2017
  5. Ronald C.

    Ronald C. FABO Gold Member FABO Gold Member

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    Do you have pics? Considering the same set up on a 74 A Body / Gen III swap
     
  6. pishta

    pishta I know I'm right....

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    I just read the hydro-boost could only be used on one circuit (ie. front) is that true?
     
  7. Ronald C.

    Ronald C. FABO Gold Member FABO Gold Member

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    I sure don’t know so please do not quote me, but I have read several updates where people are doing this on B and E body’s. And if they use them on 3500 pickups, those are 4 wheel applications
     
  8. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    Any of 'em I've seen activated the master just like any other vacuum booster
     
  9. pishta

    pishta I know I'm right....

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    This is what I skimmed over looking for Prop valve specs...maybe its been adapted...

    "Hydrovac was a common early add on for original single circuit brake system
    They work well, but only for single circuit brake systems. Modern VH44 equivalents are cheap on ebay."

    Hydro Boost With Hanging Pedals
     
  10. dodgedifferent2

    dodgedifferent2 Well-Known Member

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    Remembered to take pics today.

    I never took any pics as I did the fabrication work.

    20200212_103147.jpg 20200212_103211.jpg 20200212_103158.jpg


    This was a test setup that I used to find length. It has been floating on my bench ever since. I have the adjustable brake pushrod. So I made the adapter. I eventually just made a whole new piece from the ball to the threaded rod. I can adjust the depth of the pedal throw with the adjustable linkage.
    20200212_103300.jpg
     
  11. Ronald C.

    Ronald C. FABO Gold Member FABO Gold Member

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    Couple questions here. I would be curious to know what application the Hydro boost was originally for, and did the bolt pattern match up to the firewall or did you have to modify in order to make it fit?
     
  12. dodgedifferent2

    dodgedifferent2 Well-Known Member

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    They come from any diesel truck be it GM, ford, dodge and toyota.
    V8 Mustangs used them as well. Cant remember what years.
    Everyone seems to remember the GM Van's having them in the 90s.

    Your brand new diesel trucks still have them.

    I had to modify my mounting bracket to fit my dart because the bolt pattern is off a bit. I think every hydroboost unit will need that modification.
     
  13. Ronald C.

    Ronald C. FABO Gold Member FABO Gold Member

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    Came across one off a 05 Ram that I can pick up. Idea on if they are all the same or what it may be worth?
     
  14. dodgedifferent2

    dodgedifferent2 Well-Known Member

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  15. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    No He's referring to HydroVAC which is an entirely different animal. The way they work(ed) is, they are vacuum like a vacuum booster, but some have TWO separate hydraulic circuits. They have a slave end which the master drives, and this acuates the booster, and then an output hydraulic side, which of course goes to the brakes. These were used in older mid size trucks, and were once a "handy" add-on for things like old Jeeps

    One type here

     
    Last edited: Feb 12, 2020
    • Thanks! Thanks! x 1
    • pishta

      pishta I know I'm right....

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      Gotcha. ^^^
       
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