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Finding A Leak In Brake Lines

Discussion in 'Early CJ5 and CJ6 Tech' started by jeepstar, Jul 19, 2022.

  1. Jul 19, 2022
    jeepstar

    jeepstar Well-Known Member 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Sheboygan
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    I was driving my 70 jeep, last year I put on a Dana 30 front axle with disk brakes.
    No problems since. The other day I noticed my brake pedal was getting mushy, and eventually I had no brakes!
    Got it home safely and began looking it over. The dual master cylinder was bone dry. I refilled it, and had the wife continously pump the brakes while I crawled around under it and inspected all of the joints for any sign of leakage. No go, at least nothing obvious. Before I take it in to a real mechanic, anything else I can check?
     
  2. Jul 19, 2022
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Hills of NH
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    Look for fluid stains on the inner sidewalls of the tires, which may reveal a wheel cylinder leak.

    Or check inside the master cylinder's push-rod area or rubber boot, for leaking fluid.
     
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  3. Jul 19, 2022
    truckee4x4

    truckee4x4 Grant Kaye 2023 Sponsor 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    Did you bench bleed it before you had your wife pump thevoesal? If not you might be chasing your tail with bubbles.
     
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  4. Jul 19, 2022
    jeepstar

    jeepstar Well-Known Member 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    I did not remove the MC to bench bleed it.
    I had it all buttoned up and have been driving it since the axle swap last summer with no brake issues.
     
  5. Jul 19, 2022
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member

    Tantallon, Nova...
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    Power brakes? Might be getting sucked into your engine, noticed any funny smoke out the exhaust lately?
     
  6. Jul 19, 2022
    truckee4x4

    truckee4x4 Grant Kaye 2023 Sponsor 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    I had to completely drain mine, and when I refilled it and started over after going around and tightening up all the fittings, I got one of those cheap bench bleed kits with the clear plastic hoses and was able to connect the outputs up into the tank while it was still on the frame.

    If your spongy issue persists and you don’t see any obvious leaks you might want to give that a shot.
     
  7. Jul 19, 2022
    Buildflycrash

    Buildflycrash More or Less in Line. 2022 Sponsor 2020 Sponsor

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    How much pumping is typically involved in bench bleeding? 10,20,100 pumps?
    I need to do mine tonight - already installed but I can work out some lines easy enough.
     
  8. Jul 19, 2022
    nickmil

    nickmil In mothballs.

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    As was said check all fittings and connections, check the back of the master cylinder, check the wheel cylinders. I'd pull the rear drums (if equipped) and look inside. Gently pull back the dust boots on the wheel cylinders and look inside for wetness. If your master cylinder reservoir went dry there is a serious leak somewhere as the fluid doesn't just evaporate over time.
     
  9. Jul 19, 2022
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    More like 10-20ish, as I recall. I made the brake lines that bend back into the reservoir, and pumped until there were no bubbles. I did this with the cylinder in the vise, on the bench.

    Regarding Nick's post, if the reservoir went dry all of a sudden, that's a few ounces of brake fluid at least. I would expect it to come spraying or dripping out somewhere. It's under hundreds of PSI.
     
    Last edited: Jul 19, 2022
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  10. Jul 19, 2022
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    If it doesn't show up at a fitting or a cylinder, follow the lines and look for the wet spot on surrounding areas. As timgr says, a hole in a line will often spray.
     
  11. Jul 19, 2022
    skipilot

    skipilot New Member

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    That is odd if both chambers are empty. I would think that if it is a wheel cylinder or a caliper, then only one chamber would be empty. For finding your leak, I wouldn’t initially worry about bench bleeding. Do a good standard bleeding, if you get reasonable brakes, drive around a bit then check levels to verify if both or one chamber are going down. If you can’t get reasonable brakes then you may have to bench bleed. I have been successful not bench bleeding new masters by using 3 people so that a front and rear can be bled at the same time. Proceed from there. Good luck.
    Tim
     
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  12. Jul 20, 2022
    jeepstar

    jeepstar Well-Known Member 2022 Sponsor 2021 Sponsor 2020 Sponsor

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    Took it to the shop. Too hot out, no helper either to keep pumping. Brakes held up to the shop....
     
  13. Jul 21, 2022
    jeepstar

    jeepstar Well-Known Member 2022 Sponsor 2021 Sponsor 2020 Sponsor

    Sheboygan
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    Shop found a leak. The front drivers side flex line had a wear hole in it from something being clocked wrong and wearing. Not sure what exactly, I'll find out when I go to pick it up
     
    47v6, givemethewillys and Fireball like this.
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