Firewall brake booster modification

Brakes, Steering & Suspension

  1. Mixed-up XP

    Mixed-up XP Active Member

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    Checking in with others who may have had to modify (CUT) their firewalls for disc brake booster upgrades. I was in the process of installing a booster for my upgrading the front drums to disc. Purchased it from Dr Diff and I also got the firewall plate that goes with it. Tried installing it Sat. and it appears that I need to take some material out from the opening for it to fit. Anyone else experienced this? Just making sure before I cut a perfect firewall.
    Disc booster Dr Diff.jpg
    Here is the opening of the new booster plate outlined to the factory drum brake booster opening.
     
  2. davek

    davek FBBO Gold Member FBBO Gold Member

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    I would call Dr Diff before I would cut anything. Did put the plate up against the booster to see if it would all clear?
     
  3. Mixed-up XP

    Mixed-up XP Active Member

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    Yes, the plate that was recommended for the booster fits together perfect. I even put the factory plate over the firewall opening by itself and some of the firewall sheet metal appears in the plate opening. That's when the question of firewall mods came to mind.
     
    Last edited: Jul 18, 2021
  4. davek

    davek FBBO Gold Member FBBO Gold Member

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    but does the sheet metal interfere with anything? I believe just the rod gos threw and it should not touch anything. So I would thing its a go without cutting the firewall.
     
  5. Nate S

    Nate S Well-Known Member

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    There’s usually a phenolic boss that sticks out the back of the booster that goes through here. Real question is does that fit through?
     
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    • snakeoil24

      snakeoil24 FBBO Gold Member FBBO Gold Member

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      It does fit thru, void cutting hte firewall if you can or your going to fatigue the metal.
       
    • Nate S

      Nate S Well-Known Member

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      It won’t fatigue the metal but I completely agree, don’t cut unless required!
       
    • Mixed-up XP

      Mixed-up XP Active Member

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      I’ll do some more test fitting with the individual components and try and get some pics posted. I really want to avoid any cutting on this firewall.
       
    • snakeoil24

      snakeoil24 FBBO Gold Member FBBO Gold Member

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      if you cut too much it wilk fatigue it have to be very careful the firewall will start buckeling after repeated pedal application
       
    • 70chall440

      70chall440 Well-Known Member

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      I installed PDBs on a 69 Ply wagon and had to cut the firewall opening. The plate that goes behind the booster will eliminate any "fatigue" issues. I would not hesitate to cut it if you need to in order to get the system to fit.
       
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      • Mixed-up XP

        Mixed-up XP Active Member

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        Did some test fitting and here are some pics to show the situation. Disc booster mod 1.jpg Disc booster mod 2.jpg Disc booster mod 3.jpg Disc booster mod 4.jpg Disc booster mod 5.jpg Disc booster mod 6.jpg First pic: The flare that holds the rubber boot in place will not pass thru the firewall.
        Pic 2: New plate attaches to booster with no issue.
        Pic 3: New plate on firewall shows the fit issue.
        Pic 4: Old plate clearly does not go over the flare.
        Pic 5: Old plate still shows firewall in the opening.
        Pic 6: Shows the outline of new plate opening.
        Now, I'm sure I won't need to open the firewall that much...just did that for reference. I'll start with little touches with the Dremel until I can get it to pass thru. Not worried about metal fatigue, that's what the plate is for. Reading 70chall440's response leads me to believe that this does need to be done in rare occasions, maybe? I sifted thru quite a few threads and nowhere did I find that it was necessary to cut the firewall. That's why I posed the question.
         
        Last edited: Jul 19, 2021
      • 1968340S

        1968340S Well-Known Member

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        I'm having the exact same problem on 66 Satellite. My concern is the variance on the pedal assembly. The flare measures 2 1/2" and the pedal assembly is 2 1/4". What did you have to do? really like to know.
        I've tried several ways to get in touch with DrDiff with no luck.
         
      • chtampa

        chtampa FBBO Gold Member FBBO Gold Member

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        Never had to modify a firewall for a booster. I would only modify a part, not a car.
         
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        • Redsawacs

          Redsawacs Well-Known Member

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          If the car is originally a manual brake car, you will have to buy either a booster kit with a force multiplier rod assembly or you will have to swap the manual brake pedal to a power brake pedal. Either way, I think you have the wrong booster of you have to cut the firewall to get it to fit.
           
        • Ron H

          Ron H FBBO Gold Member FBBO Gold Member

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          Appears FW was already 'modified'..
           
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