1968 Power Disk Brake Conversion

Discussion in 'Ranchero Tech Help' started by 68-Ranchero, Aug 4, 2019.

  1. 68-Ranchero

    68-Ranchero In First Gear

    Messages:
    7
    Location:
    Dallas, Tx
    I have converted 4 wheel drum brakes on a '68 Ranchero to front wheel power disk. Everything is new, Master Cyl, Distribution Valve, Calipers, Rotors, Hoses both front and single rear to axle, used a Rebuilt Original '69 Power Booster and a Rebuilt/New Master Cyl.
    Everything has been installed. The brakes have been bleed multiple times with a power bleeder. I do not have any brake pedal, unless the power bleeder is hooked up to the system.
    I pre-bleed the master cyl. before installation.
    I have plugged the master cyl. ports, tested the pedal and the pedal is firm. Hooked it back up, no brakes.
    I have removed the calipers and turned them so the bleed ports were straight up and bleed them again, no brakes.
    The rear brakes have been adjusted using a brake shoe caliper, no extra play.
    The master cyl. is for disk brakes with the rear brake port on the front of the unit pointing down and the front brake line pointing to the left side at the top of the shock tower.
    The calipers are single piston type.
    There are no brake line leaks.

    Any ideas as to why there are still no brakes?
    1.) Still air in the lines?
    2.) Bad master cyl., even though pedal is hard when the ports are plugged?
    3.) Wrong master cyl. for the the calipers? Not enough volume in '69 Master Cyl. for Single Cyl. calipers?
     
  2. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

    Messages:
    9,381
    Location:
    Everett, WA
    Does the system have a pressure differential valve, rather than just a distribution block? The PD valve is necessary with front disc brakes, and made more effective with a two-chamber master cylinder. If you do have one, the piston is supposed to be pulled forward and held, while bleeding the system.
     
  3. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

    Messages:
    9,381
    Location:
    Everett, WA
    I think I posted some diagrams for another member, and I may still have them on my computer. If I don't, I can post up pics from my Motor manual.
     
  4. 68-Ranchero

    68-Ranchero In First Gear

    Messages:
    7
    Location:
    Dallas, Tx
    Yes, It has a pressure differential valve. It has been manually locked in place to keep it from moving while the brakes are bled. Once I get brakes, I'll reinstall the brake warning switch.
     
  5. 68-Ranchero

    68-Ranchero In First Gear

    Messages:
    7
    Location:
    Dallas, Tx
    Also, the master cyl. has two Reservoirs for front and rear brakes.
     
  6. Hillbilly

    Hillbilly In Maximum Overdrive

    Messages:
    5,634
    Location:
    Winchester, TN.
    Something I found on rebuilt boosters. You have to match the pushrod out of the booster to the depth of the bore in the master cylinder piston. If the booster rod is too short it will give static brake pedal feel but not push the master cylinder piston far enough to move the wheel cylinders. The rod should have an adjustable extension on it to allow setting it to the correct depth. Another potential, did the booster come with the firewall mounting pedestal including the rocker mechanism that goes inside to connect with the brake pedal ? If it did come with it, did the arm that connects to the brake pedal line up with the pin on the pedal straight or is it at an odd angle ? If it isn't a straight shot to the pedal you are loosing travel needed to fully push the master cylinder as needed. Some cars of that era had different pedals with the pin located differently for manual brakes v/s power assisted brakes. Check those two things before replacing the master cylinder. If you can't get the master cylinder push rod adjusted out far enough then the rebuilder used the wrong piston in the master cylinder, one with too much depth. It happens.
     
  7. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

    Messages:
    9,381
    Location:
    Everett, WA
    The specification for the length of pushrod from the mounting face of the booster to the pushrod end is .958", +/- .002". Make sure the pedal has between 1/4 and 1" travel when reassembled.
     
  8. 68-Ranchero

    68-Ranchero In First Gear

    Messages:
    7
    Location:
    Dallas, Tx
    Hillbilly - I have a copy of the 1968 Fairlane Shop Manual - on page 2-4 is a picture of what they call a Push Rod Gauge to adjust the booster push rod. I used it to make a template copy to set the push rod length on the brake booster. I had to make a very minor adjustment to the rod, but it didn't make any difference. Yes, I got all the mounting brackets and linkage with the flat brake pedal connector rod that connects to the brake pedal . The brake pedal is also from a Disk Brake car. It has the disk brake pad on it. I have more than one and they are both the same. They are different than the four wheel manual brake pedal.
    The flat connecting rod that comes from the booster to the pedal lines up to the brake pedal pin/mount. It goes straight to the pedal and is not angled up or down from the booster. Everything fits and looks right according to the brake diagrams in the shop manual.
    On this setup the rod to the master cyl. is part of the booster and fits into the back of the master cyl. without a locking clip. Before the change over it was set up with manual four wheel brakes and the rod was locked into the master cyl. piston.
    Any other suggestions?
     
  9. 68-Ranchero

    68-Ranchero In First Gear

    Messages:
    7
    Location:
    Dallas, Tx
    When converting this '68 Ranchero to disks, I went to a junk yard and pulled all the power brake booster and brake parts from the car. All except the proportioning value, which was already removed. Everything has been rebuilt, (booster) or replaced with new parts (calipers, rotors, spindles, hoses, master cyl., proportioning valve) or used parts (booster linkage, booster bracket, brake pedal). This is what is so perplexing. It should all bolt together and work. But it doesn't.
     
  10. Hillbilly

    Hillbilly In Maximum Overdrive

    Messages:
    5,634
    Location:
    Winchester, TN.
    Possibility you got a bad master cylinder. Did the master cyl. look like it had set on a shelf for a long time ? Seen quite a few lately that obviously had been remanufactured but had deteriorated internally, mostly 4 wheel disc cylinders for Corvettes but a few for early 70's Fords.
     
  11. 68-Ranchero

    68-Ranchero In First Gear

    Messages:
    7
    Location:
    Dallas, Tx
    I have what looks like an original Ford master cyl.,
    It is suppose to be a new master cyl. according to the box. It is sold as new and looks new vs. a rebuilt.
    I took exchanged the master cyl. today for another "new" one.
    I also took the booster back to the rebuilder to have it bench tested for a vacuum leak. The engine would stumble and run rough when the brake was pushed. When the brake was released, it would run smooth.
    The booster should be available again, early next week. I'll put the new master cyl. and the booster back in, pressure bleed the brakes and see if anything has changed.
     
  12. csilva73-500

    csilva73-500 In First Gear

    Messages:
    5
    Does your booster have it's own vacuum source with nothing else hooked to it. If not then try and find one. Also have you tried to bleed the brakes the good old fashion way with someone behind the wheel pumping the brakes. Are they able to pump up the brakes? Sometime pressure bleeders, especially vacuum pressure bleeders can introduce air into the line. Good luck.
     
  13. 68-Ranchero

    68-Ranchero In First Gear

    Messages:
    7
    Location:
    Dallas, Tx
    Yes, the booster has only one new hose connected from the base of the carb. directly to the booster without any other connections.
    I have not tried to bleed the brakes manually yet. I am using a pressure bleeder that clamps to the top of the master cyl. using 20 psi. in the bleeder. It should be able to push any air out the bleeder ports.
    Once replacing the parts, if pressure bleeding doesn't work, I'll try to manually bleed the brakes.
    Thanks for your assistance. It will be next weekend before I will have time to put it back together.
     

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