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Under-Cab Power Brakes and Dual Master

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  • Under-Cab Power Brakes and Dual Master

    For the last few years I've been designing a way to mount a vacuum boosted dual master cylinder on my 6x6 Power Wagon, while keeping the stock brake and clutch pedals. The last few months have been spent researching different parts and designing a mounting bracket for the system. This is what I've come up with so far:



    This is a GM style master cylinder with 1 1/4" bore. The booster is a 7" single diaphragm unit from Tuff Stuff, and bolts directly to the master cylinder with no modifications. An 8" booster will probably fit in the same location, and a double diaphragm booster would add about 1 1/2" to the overall length. My truck doesn't have a PTO on the transmission, but from what I can tell there will be plenty of room for both the PTO and the master cylinder. This setup won't work with a rear PTO system.

    The mounting bracket will look something like this:



    The bracket will mount to the transfer case cross member, and should place the master cylinder under the driver's floorboard. I won't know for sure how the alignment works until the cab is mounted to the frame, sometime this year. For a long time I was trying to find a place to mount the bracket using existing bolt holes in the frame, but it never worked very well. This bracket will need 4 holes drilled in the lower flange of the cross member, which won't affect its strength.

    There's still some design work to do on the bracket, but I'm 90% done (I hope). I'll post more pictures once I have the steel bracket fabricated.
    Greg Coffin
    Unrepentant Dodge Enthusiast

    1951 Dodge M37 - Bone Stock
    1958 Dodge M37 - Ex-Forest Service Brush Truck
    1962 M37-B1 - Work in Progress
    1962 Dodge WM300 Power Wagon - Factory 251, 4.89s
    1944/1957 Dodge WM500T 6x6 Power Wagon - LA318-3, NP435, 5.83s, Power Steering, Undercab Power Brakes
    1974 Dodge W200 - 360/727, Factory Sno-Fighter Package

  • #2
    Greg,

    Nice, looking forward to more details and pictures. I'm assuming your non-power MC was already an under cab installation?
    I drive a DODGE, not a ram!

    Thanks,
    Will
    WAWII.com

    1946 WDX Power Wagon - "Missouri Mule"
    1953 M37 - "Frankenstein"
    1993 Jeep YJ - "Will Power"
    1984 Dodge Ramcharger - "2014 Ramcharger"
    2006 3500 DRW 4WD Mega Cab - "Power Wagon Hauler"

    Comment


    • #3
      No, it it in the stock location under the steering box. I'll run a new brake rod through the spring port in the pedal support casting. There's just enough room to get the rod through. The rod is in tension during braking, which I like because it needs to be about 20" long, and in compression it would likely bend during hard braking - not a good thing!
      Greg Coffin
      Unrepentant Dodge Enthusiast

      1951 Dodge M37 - Bone Stock
      1958 Dodge M37 - Ex-Forest Service Brush Truck
      1962 M37-B1 - Work in Progress
      1962 Dodge WM300 Power Wagon - Factory 251, 4.89s
      1944/1957 Dodge WM500T 6x6 Power Wagon - LA318-3, NP435, 5.83s, Power Steering, Undercab Power Brakes
      1974 Dodge W200 - 360/727, Factory Sno-Fighter Package

      Comment


      • #4
        Awesome! Good Job. Looking forward to more details. I would love to add this to my FFPW.

        Comment


        • #5
          If the prototype works well I may offer the bracket or system as a kit. I'll keep you posted.
          Greg Coffin
          Unrepentant Dodge Enthusiast

          1951 Dodge M37 - Bone Stock
          1958 Dodge M37 - Ex-Forest Service Brush Truck
          1962 M37-B1 - Work in Progress
          1962 Dodge WM300 Power Wagon - Factory 251, 4.89s
          1944/1957 Dodge WM500T 6x6 Power Wagon - LA318-3, NP435, 5.83s, Power Steering, Undercab Power Brakes
          1974 Dodge W200 - 360/727, Factory Sno-Fighter Package

          Comment


          • #6
            Perfect! Thanks.

            Clark

            Comment


            • #7
              Under floor power brakes

              Did the master and booster work?

              Comment


              • #8
                The parts for the bracket are getting cut out this week. I hope to weld it up this weekend, and install it soon after that. I'll post more info as things progress.
                Greg Coffin
                Unrepentant Dodge Enthusiast

                1951 Dodge M37 - Bone Stock
                1958 Dodge M37 - Ex-Forest Service Brush Truck
                1962 M37-B1 - Work in Progress
                1962 Dodge WM300 Power Wagon - Factory 251, 4.89s
                1944/1957 Dodge WM500T 6x6 Power Wagon - LA318-3, NP435, 5.83s, Power Steering, Undercab Power Brakes
                1974 Dodge W200 - 360/727, Factory Sno-Fighter Package

                Comment


                • #9
                  Measure Once, Cut Once....

                  I picked up the steel parts for the brake system bracket from the water jet shop, but the weekend was busy and no welding happened. The parts are beautiful, and exactly what I ordered. The edges are remarkably crisp, with no melt-over and flash like you see with plasma cut parts. They are also quite sharp, and I had to be relieved them with a file and deburring tool or I would have cut myself.

                  The bad new is the parts are exactly what I ordered. Re: I had to slot the holes for the booster mounting studs. I was told that the booster studs are laid out in a 3-1/2" square, but when I tried to mount the booster to the bracket the studs didn't line up. They are more like 3-3/8" center to center. That's what I get for not measuring the studs before hand. The question now is are all (GM style) booster studs laid out at 3-3/8", or do I have to cut slots to accommodate variations in stud layout.

                  Next I have to lay out the mounting holes for the top plate. After that it's layout for the pivot point, and build the pivot system. I'll post photos as things progress.
                  Attached Files
                  Greg Coffin
                  Unrepentant Dodge Enthusiast

                  1951 Dodge M37 - Bone Stock
                  1958 Dodge M37 - Ex-Forest Service Brush Truck
                  1962 M37-B1 - Work in Progress
                  1962 Dodge WM300 Power Wagon - Factory 251, 4.89s
                  1944/1957 Dodge WM500T 6x6 Power Wagon - LA318-3, NP435, 5.83s, Power Steering, Undercab Power Brakes
                  1974 Dodge W200 - 360/727, Factory Sno-Fighter Package

                  Comment


                  • #10
                    Excellent! Keep it coming!

                    Clark

                    Comment


                    • #11
                      Bracket Fabrication

                      I played hookey from work today and spent some time on the prototype bracket. First I sand blasted the parts, and then ran my layout lines. The gusset plates fit very nicely. I beveled the outside edge of the main gusset so that I would have a groove to fill with the weld. I located and drilled the mounting holes for the top plate, and the holes for the lever axle.

                      The welding didn't go as well as I hoped. I was running the welder a little too hot and overheated the steel, and got some warping in the top plate and mounting face. But I got great penetration. After backing off the heat a bit the welding went better, and I was able to straighten out most of the warpage. This bracket is mostly a prototype, and I'm going to have a pro welder friend do the next bracket, once all the bugs are worked out of this one.

                      Here are a few photos
                      Attached Files
                      Greg Coffin
                      Unrepentant Dodge Enthusiast

                      1951 Dodge M37 - Bone Stock
                      1958 Dodge M37 - Ex-Forest Service Brush Truck
                      1962 M37-B1 - Work in Progress
                      1962 Dodge WM300 Power Wagon - Factory 251, 4.89s
                      1944/1957 Dodge WM500T 6x6 Power Wagon - LA318-3, NP435, 5.83s, Power Steering, Undercab Power Brakes
                      1974 Dodge W200 - 360/727, Factory Sno-Fighter Package

                      Comment


                      • #12
                        Very nice! Can't wait to see it bolted in place.

                        Comment


                        • #13
                          Bracket Temporary Installation

                          Here are a few more photos from today.
                          Attached Files
                          Greg Coffin
                          Unrepentant Dodge Enthusiast

                          1951 Dodge M37 - Bone Stock
                          1958 Dodge M37 - Ex-Forest Service Brush Truck
                          1962 M37-B1 - Work in Progress
                          1962 Dodge WM300 Power Wagon - Factory 251, 4.89s
                          1944/1957 Dodge WM500T 6x6 Power Wagon - LA318-3, NP435, 5.83s, Power Steering, Undercab Power Brakes
                          1974 Dodge W200 - 360/727, Factory Sno-Fighter Package

                          Comment


                          • #14
                            The Eagle has Landed!

                            I got the bracket installed yesterday. Overall I'm very pleased with it. There are some minor geometry issues that I have to deal with, but I expected some of that. The main issue is that I'm only getting about 80% of the master cylinder stroke when the pedal travels its full stroke. There are a couple ways to deal with that, the easiest is to add 1/2" to the master cylinder lever arm. The bad news is I can't modify this current bracket without tearing it all apart, so I'll have to make the changes and build another bracket.

                            Whether I actually need 90-100% stroke on the master cylinder is another question that I don't have the answer to. My assumption is that when the brake pedal hits the floorboard the master cylinder should be at the end of it's stroke. I know that the pedal in my WM300 only travels 3 1/2" to engage the brakes, with a total of 9" travel to the floorboard. Both master cylinders have the same bore size (1 1/4"), so this one might behave the same way. If anyone has some input on this, I'd be happy to hear it.

                            The next thing to do pull the bracket off and paint it, then bend up some brake lines to connect the master cylinder to the chassis lines and bleed the system. If I can find a small vacuum pump I'll hook it to the booster and see how the pedal feels.

                            One advantage to increasing the length of the booster arm is that it lowers the center line enough to fit an 8" booster under the cross member. I've read that a 8" double diaphragm booster has as much punch as a standard 11" unit, so you can get plenty of boost in a fairly small package. I don't want that much boost, so I opted for a 7" single diaphragm booster.
                            Attached Files
                            Greg Coffin
                            Unrepentant Dodge Enthusiast

                            1951 Dodge M37 - Bone Stock
                            1958 Dodge M37 - Ex-Forest Service Brush Truck
                            1962 M37-B1 - Work in Progress
                            1962 Dodge WM300 Power Wagon - Factory 251, 4.89s
                            1944/1957 Dodge WM500T 6x6 Power Wagon - LA318-3, NP435, 5.83s, Power Steering, Undercab Power Brakes
                            1974 Dodge W200 - 360/727, Factory Sno-Fighter Package

                            Comment


                            • #15
                              That is a sweet set up!

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