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  • davpratt
    started a topic Adding a dual brake booster to a '74 J10

    Adding a dual brake booster to a '74 J10

    I've been working on adding a brake booster to my truck.

    I found a '79 J20 in the scrap yard and I pulled the booster assy.
    I have manual drum brakes on my truck.

    After removing the master cylinder from the fire wall, I had to remove three more bolts to install the booster to the fire wall.

    I have run into a problem with the pin used to operate the brake booster.
    The manual brakes have a 1/2"dia pin.
    The brake booster has a 7/16" dia hole.

    I bought a new double booster for a '74 J10 truck and its the same as the "79 J20 truck.

    Also, the angle of the push rod is different because of the allumnum spacer shifts the booster slightly upward, and if I changed the dia of the pin on the pedal, the pedal would be closer to the floor because the rod built into the booster is shorter. The angle prevents the pedal pin location to push squarely against the brake booster.

    I returned to the scrap yard and retrieved the 79 brake pedal assy. The assy is for a truck with an automatic transmission.
    I cut the rivets to remove the wide plate, everything seems the same except the angle of the pedal. It's straighter. The cast lines show it is designed that way.

    I installed the Automatic truck pedal, but the brake pedal is still, for me, to close to the floor. It doesn't lign up with the height of the clutch pedal. ( The manual brake pedal is higher than the clutch. It would be nice if the are even.)

    I also found the pin is in a different location on the automatic truck brake pedal. The 7/16" pin is moved closer to the engine bay and does lign up to the push rod in the booster nicely.

    The manual brake pedal has an area for the 7/16" pin. Both pedals have the same cast iron design in the area of where the pins are located.

    I've decided to drill the manual brake pedal and insert a 7/16" grade 8 bolt in the general location of where the automatic truck brake pedal has its pin. The bolt is made 3" long and I'll have to cut the threads off that aren't needed. I will put a locking nut on the left side of the pedal so the shoulder of the bolt is used to push the rod. Not the threads.
    This will keep the push pin in a straight line into the brake booster. Removal of the manual pin is not neccessary it doesn't interfear with the 7/16" location.

  • davpratt
    replied
    I took some pictures.
    The 'autobrakepedal' shows how much lower the automatic brake pedal sits.

    The 'brakepedaldiff" shows the difference in the two pedals. The straight pedal is the automatic. The more curved pedal is the manual type. You can see where I drilled the hole of the grade 8 bolt.

    The 'normalgrakepedalpos' is where the pedal is and is now in the same location it was before adding the brake booster.

    A pic of the new power booster installed. 'newpowerbooster'
    Attached Files

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