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Thread: 1940 J4A Master Brake Cylinder

  1. #1
    Wag2+2's Avatar
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    1940 J4A Master Brake Cylinder

    Anyone happen to have a source for a used in working condition master cylinder? A new one is quite pricey. Thanks.

  2. #2

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    I heard they can be rebuilt with an auto master cylinder repair kit.

    I rebuilt a pair of UPF-7 masters - it was NAPA kit#1.
    Likes Steve Pierce liked this post

  3. #3
    cubdriver2's Avatar
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    Which one?



    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  4. #4
    Steve Pierce's Avatar
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    Quote Originally Posted by bob turner View Post
    I heard they can be rebuilt with an auto master cylinder repair kit.

    I rebuilt a pair of UPF-7 masters - it was NAPA kit#1.
    Yep, fixed the leaking master cylinders on the Hamilton Metal Plane over at New Holstein the year of Sloshkosh with that kit.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  5. #5
    Wag2+2's Avatar
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    Thanks guys. Will check into which cylinder Glenn.
    Last edited by Wag2+2; 05-25-2020 at 04:11 PM. Reason: Added

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    seems like the last time i did mine the kit was for a 58 chevy.
    Thanks RVBottomly thanked for this post

  7. #7
    wireweinie's Avatar
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    Quote Originally Posted by Steve Pierce View Post
    Yep, fixed the leaking master cylinders on the Hamilton Metal Plane over at New Holstein the year of Sloshkosh with that kit.
    Will those seals handle petroleum products like 5606?

    Web
    Life's tough . . . wear a cup.

  8. #8
    Wag2+2's Avatar
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    Looks like it might be the top one Glenn.
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  9. #9
    Cub Builder's Avatar
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    Quote Originally Posted by wireweinie View Post
    Will those seals handle petroleum products like 5606?

    Web
    Isn't the J-4 supposed to use DOT-3? Mine did.

    -Cub Builder

  10. #10
    SuperCub MD's Avatar
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    5606 worked fine in these brakes for me. The old Wagner cylinders with Napa seals could stop double puck Clevelands with bushwheels on a dime and give you change.
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  11. #11

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    Yes to Dot 3. Ours came with 5606, so I stuck with it.

    I have been using Dot 5 on the J3s, but it s now $40/pint, and since both use MS O-rings everywhere, I may succumb. I will, however, use inverted flares until they are no longer available.
    Likes RVBottomly liked this post

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