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Thread: Master Cylinder Swap

  1. #1

    Default Master Cylinder Swap

    I've got a 68 M715 with stock axles, brakes, hoses, and Lines. The mastercylinder is junk and therefore needs some type of work. I was wondering if anyone has swapped a mastercylinder out of a 78 J-10 or Wagoneer or anything like that? I've got a parts Wagoneer and was hoping it would work.

  2. #2
    Join Date
    Dec 2003
    Location
    West-central Ohio
    Posts
    689

    Default

    There has been some discussion regarding the "best" M/C update - it's generally accepted by all that upfitting to a dual system is a "must-do".

    Some feel the drum-drum early corvette M/C is the better route, as the F/R volumes are equal, as should be with OUR common F/R - drum/drum systems.
    "other peoples junk, is something or other" - Militarypotts 02/07/2011

  3. #3
    Join Date
    Jan 2007
    Location
    Fort Smith, Arkansas
    Posts
    911

    Default

    The FSJ one you have should bolt right up. I put one for a 70 J-20 in mine. I went this route becuase I needed a part from a truck with the drum/drum setup. The pedal is a little hard now as reported by several other members as well. If yours is the power brake setup, I think you may have to mod the brake plunger rod but I'm not for certain. Don't know how the different size / proportioning front to rear might affect the brakes. Hope that helps.

  4. #4
    Join Date
    Sep 1998
    Location
    North Central Wisconsin
    Posts
    11,520

    Default

    I know this about Jeep master cylinders as one of our members went through a TON of research to find it out:

    Source of master cylinder part number: Wagner, Alabama Plant, product engineering.

    Master Cylinder: Wagner #F66857
    Same unit by other manufacturers: Raybestos #36246, A1 Cardone #A-1-10-1331.
    At fire wall: bolts right on, no modifications necessary, use stock brake pedal and push rod.
    Outlets are threaded for 1/2-20 and 9/16-18.
    Steel nuts for 1/4" brake line are Edelmann #121045 and Edelmann #121049. You will need a double flare tool to make up 1/4" brake lines for them. In the front brake circuit don't terminate 3/16" line at the master cylinder, the brass flair cone is too big. Use 1/4" line and convert to 3/16" line down at the tee fitting you'll need to install down at the frame where the two front lines are near each other.
    The primary circuit is the rear brake circuit.
    The secondary circuit, nearest
    firewall, is the front brake circuit. A proportioning valve isn't necessary.
    You have several options from here, but you MUST split the lines between front and rear.
    I replaced all the lines with 1/4", removed the hydraulic brake switch and installed a mechanical switch at the brake pedal (JB welded a limit switch on the steering column directly between it and the brake pedal, a standard cylinder type brake switch can be installed on the existing braket). The wiring from the old switch will reach these locations. The tee located at the left front wheel flex hose connection will need to be
    changed to one with 1/4" connections.
    If you choose to keep the 3/16" brake lines and the hydraulic brake switch: Put the brake switch in the rear brake circuit. Put plugs in the two outlets that went to the front
    circuit.
    CAUTION: If you can't position the hydraulic switch in a manner that will not trap air in the plugged section or the switch section, don't use it.
    If you want to use DOT 5 brake fluid, be sure to get a new brake switch to avoid the possibility of melting the seals.
    If you want to use DOT 5 brake fluid, be sure to get new flex hoses, 2 on front, one at rear axle.
    Wheel cylinder rebuild kit is Wagner #F3609, this kit has upgraded boots, seals and springs - others mfgs do not. Get new bleeder screws Wagner #F11579, these have BIG wrench flats and stick out farther so you can reach them. Wheel cylinder pistons are not available, if you need some, you'll need to buy some other 1-1/16" diameter wheel cylinder. Try Wagner #F35472, F41718 or F73614; they're expensive, but you'll get steel or stainless steel pistons out of them.

  5. #5

    Default Brakes on M715

    Nice to read from somebody who knows something on brakes.
    However, to improve the brake balance, go to 15/16 rear cylinders EIS EW9150/EW9151 or Raybestos WC17509/WC17510 (a little work with a file is required). Brake performance will rise to 63% without rear locking wheels. As master cylinder also th CJ7 Drum/Drum 1" works fine. I use it since almost 20 years. Add a booster, and braking will be like a passenger car!

  6. #6
    Join Date
    Jan 2007
    Location
    Georgetown, CA
    Posts
    418

    Default

    You can take the power booster off the wagoneer and use it also. You will need the little aluminum adapter behind it, and drill a couple of holes in the firewall, then mount it up. The rest of the conversion it listed above. The power brakes are AWESOME!! Makes driving it completely different. You will also need to modify the mounting of the pushrod on the pedal, as the size of the hole is different. I bolted a piece of 1/4 in plate onto the pushrod drilled a hole in it for the original pushrod pin, ..works like a charm. . .this is one modification that is well worth the effort. It also means that you now have a master cylinder that you can get cheap at a#tozone, or similar stores, and they will have it in stock!!

  7. #7

    Default

    Anyone know what years the Wagoneer had the right brake booster, or will any model year work for it?

    Zach

  8. #8
    Join Date
    Jan 2007
    Location
    Georgetown, CA
    Posts
    418

    Default

    My booster and MC came off a 77 J-20 pickup. The 79 Cherokee uses the same one, both had 360 V-8, but I don't think engine application makes any difference.

  9. #9

    Default

    Does the brake booster require vacuum from the engine? Or Power steering for a fully hydrolic unit?

    Zach

  10. #10
    Join Date
    Jan 2004
    Location
    Washington State
    Posts
    1,652

    Default

    I would possibly rethink the brake booster idea. Especially if you decide you might go another route with a v-8 engine. To me it was most important to have good power steering, good clutch pedal, good brakes. I used a hydraulic clutch setup and it is phenomenal. The sacrifice was for me not being able to use a brake booster easily. I do however have front disc brakes, stock rear drums rebuilt. And an 1980 chevy one ton truck dual master cylinder. The brakes are still braking in or seating and they a very good. Similiar pedal feel to stock but getting better. I am very happy I spent the time with the hydraulic clutch stuff. The clutch is car like. I have adjustable pedal height I built into the stock clutch mounting bracket. I can keep my heel on the floor and clutch all day long with ease. Just something to think about. Good luck on your decision.

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