1. Duke5A

    Duke5A Well-Known Member

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    Contemplating a hydro boost swap on my car. Does anyone have the dimensions of the four studs on the back of the brake booster that mount through the firewall? I'm wondering if any of the pre-made adapter plates for older Mopars will be the correct dimension or if I'll have to make my own.

    Thanks...
     
  2. 89.Fifth

    89.Fifth Well-Known Member

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    This isn't going to be 100% accurate but I took an image from rock auto and scaled the image until it the booster was 11" diameter. That gave me a 3.51" dimension center to center on the short side, 3.625 on the long side, and 5.03" on the diagonal.
     
  3. BudW

    BudW Moderator Staff Member

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    Not at the top of my head.

    A bit unrelated but my ’97 Dodge ¾ ton diesel pickup came with hydroboost. The gas engines came with vacuum brake booster. My previous ’94 diesel pickup had vacuum brake booster with a vacuum pump on it. Interesting though, is the vacuum pump is the same on both the ’94 and ’97 diesels, just one does only cruise and A/C controls where the other also does brakes.

    Getting back to your point, if a person can find what the specs are for a brake booster for ’94-01 Dodge pickup, for the measurements should be the same. I do know they were metric and If I was to guess, I would assume to be the same as a K-car – but can’t recall. I had to replace the hydroboost on my ’97 about a decade ago. Not fun.

    It looks like same unit that is used in many GM and Ford pickups – but never done a side by side comparison though.


    I have a ‘68ish B-body power brake backing plate laying on the floor in my garage and a rebuilt brake booster that hasn’t seen the light of day in twenty years. I can dig both out and take some pictures for you – if wanted.
    I can’t access my pickup at the moment to do any measurements on it.
    BudW
     
  4. Camtron

    Camtron Well-Known Member

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    I know they have them for D100s and caravans and such from our cars decades and all the pages mention “will work on just about anything”, wonder if they’d be a straight bolt on replacement. I’ve also seen some B-body guys mention their hydro conversion kits were just relabeled GM hydro boosters.
    Anyway, this is the page I had bookmarked the other night. Figured one of them would probably work.
    Dodge, Chrysler, Plymouth
     
  5. Oldiron440

    Oldiron440 Well-Known Member

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    How do you figure out what you need?
     
  6. BudW

    BudW Moderator Staff Member

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    I dug out the parts from my garage.
    My brake booster bracket ended up not exactly as I remembered it to be:
    20191023_102329r.jpg
    A ’66-70 B-Body non-power brake stiffening plate. I’m not even sure why I even have it.


    This booster and master cylinder I had purchased 20ish years ago for my ’68 Charger and was to look like this:
    69 B Body wMC.jpg

    The box had never been opened but had sustained water damage from garage roof leak. The box had to be carried from underneath or would have come apart.

    This is a tandem booster but is huge. I should have opened the box after getting it (my bad). I'm not even sure what this fits (way overkill for an FMJ)

    It does fit my ’84 Gran Fury (M-Body) petal set, though.
    20191023_103010r.jpg

    20191023_103016r.jpg

    Going back to the nut question.
    The part number for booster (hydra or vacuum) to firewall for a ’97 pickup is 6503269 (M10-1.5, locking (pinched)). For booster to master cylinder is 6503073 (M10-1.5, Nylock).

    I don't think it matters what design lock nut you use, but use something that keep the brakes in place (we want to keep you around here, for a long while).
    Lock Nuts.png
    Top Left - pinched (or full metal), Top Right - Nylon insert.
    Bottom Left - Serrated flange, Bottom Right - Captive lock-washer.

    BudW
     
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  7. Duke5A

    Duke5A Well-Known Member

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    @BudW: It fits on the horizontal, but vertically it's farther spread apart. Could you by chance measure the center to center of those bolt holes on the pedal assembly going vertical and horizontal? Probably going to have to make a plate to bolt the hydroboost unit to the firewall. No big deal I suppose. Buddy of mine has a bridge-port in his garage.
     
  8. BudW

    BudW Moderator Staff Member

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    Just now read this post.
    I will perform some measurements from my ’84 Gran Fury booster tonight and will post, soon.
     
  9. BudW

    BudW Moderator Staff Member

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    I performed some measurements last night.
    These were taken from the original booster from an ‘84 Gran Fury (same as any other FMJ booster).
    Top two studs:
    20191101_233909c.jpg

    20191101_233857c.jpg
    3.038” inside / 3.615” outside – 3.33” center-to-center

    Bottom two studs:
    20191101_233919c.jpg

    20191101_234021c.jpg
    3.031” inside / 3.638” outside – 3.33” center-to-center

    Passenger side studs:
    20191101_234107c.jpg

    20191101_234036c.jpg
    3.282” inside / 3.814” outside – 3.55” center-to-center

    Drivers side studs:
    20191101_234118c.jpg

    20191101_234133c.jpg
    3.295” inside / 3.803” outside – 3.55” center-to-center

    To recap:
    Top studs are 3.33” apart (all are center-to-center)
    Bottom studs are 3.33” apart
    Passenger studs are 3.55” apart
    Drivers studs are 3.55” apart

    I hope this helps.
    BudW
     
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  10. XfbodyX

    XfbodyX Well-Known Member

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    You can also toss this in the mix, less then $100 for more flexibility.

    If I might ask why a HB setup, alot of times they are just a pain and some dont last so long. As mentioned diesel and turbo cars use them.

    Have you considered a lil ele vac pump for your brake system.

    I need to go back and read, but what is the end goal here?

    Brake.jpg
     
  11. Duke5A

    Duke5A Well-Known Member

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    @BudW Holey smokes Bud, that is exactly what I needed. Thank you! Even with photos.

    @XfbodyX It started with an exorbitant amount of swearing and frustration working around the booster when I replaced the head gasket in August. I want it gone. The motor develops enough vacuum to operate it though. Was contemplating going to a multi-piston caliper up from with a larger rotor with manual brakes at first, but then I drove a friend's car with a retrofitted hydroboost setup and I was sold. I should be able to get a parts store reman GM unit for not too much and make my own adapter this winter thanks to Bud's measurements. What's the deal with that adjustable master cylinder rod?
     
  12. XfbodyX

    XfbodyX Well-Known Member

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    Thats a fit all mopar type adjustable rod sold by Dr. Diff.

    I understand on the HB, just be aware the GM units suck and dont last long for some reason, I had 12 replaced under warrenty in 3 years in a mid 80-s GN.
     
  13. XfbodyX

    XfbodyX Well-Known Member

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  14. BudW

    BudW Moderator Staff Member

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    I think that ’84 Gran Fury booster assembly, that has been sitting outside in the elements for last decade, has been more useful than not.
    I’m not really sure why I even kept it – for it will never get bolted up to anything.