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How Much Psi Is Too Much

Discussion in 'Flat Fender Tech' started by garage gnome, Jun 30, 2019.

  1. Jun 30, 2019
    garage gnome

    garage gnome Rust polisher Sponsor

    Western MA
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    I have on board air on my Jeep and I was thinking of putting a valve to pressurize the differentials and transmission and transfer case. I was thinking of 5psi to pressurize them for deep water. Is that too much?
     
    Last edited: Jun 30, 2019
  2. Jun 30, 2019
    PeteL

    PeteL Member Sponsor 2019 Sponsor

    Hills of NH
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    M38A1 used unregulated pressure from the crankcase but I don't know what that would be. I'd be interested to find out.

    According to this thread, M35 used regulated air at 4 psi.
    Home Made Fording Kit? - Page 3


    Be aware, as they point out, the military protocol called for major overhaul work after each deep-water fording, even with sealed and pressurized systems.
     
  3. Jun 30, 2019
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member Sponsor

    Tantallon, Nova...
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    I'd say so, you only have to pressurize them to match to external pressure, conveniently measured in "inches of water". Let's say the lowest you'll submerge anything is 12", so you need to pressurize that much- 12"/H2O = ~ 1/2 PSI.

    The reality is water usually gets sucked into things when it cools down the axle/xfercase/tranny/whatever & creates a lower pressure inside- as long as you're vented to a point above the water to allow equalization you're probably good.
     
    Last edited: Jul 1, 2019
  4. Jul 1, 2019
    Jeepenstein

    Jeepenstein Me like Jeep.. Sponsor

    Middle TN
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    static water pressure is roughly 4 PSI/10 feet..
     
  5. Jul 1, 2019
    Howard Eisenhauer

    Howard Eisenhauer Super Moderator Staff Member Sponsor

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    If your axle is under 10 feet of water you have other problems :rolleyes:
     
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  6. Jul 1, 2019
    rejeep

    rejeep Well-Known Member Sponsor 2019 Sponsor

    Rochester, NY
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    how much deep water do you drive through?
    for a trail rig I would say a good working vent is all you really need...
    for an apocalypses vehicle... maybe, but again bigger concerns..
     
  7. Jul 1, 2019
    GeorgiaFlattie

    GeorgiaFlattie New Member

    Canton, GA
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    Exactly, make sure the vent hoses are in good shape and routed to the top of ther firewall or even up under the dash if you're paranoid.
     
  8. Jul 1, 2019
    garage gnome

    garage gnome Rust polisher Sponsor

    Western MA
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    Just figured the military jeeps had that feature. Thought it would be a good idea.

    All my vents are up high anyways.
     
  9. Jul 1, 2019
    PeteL

    PeteL Member Sponsor 2019 Sponsor

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    Would you include the carb, fuel tank, and the distributor, plus sealing the alternator, regulator etc, as the M38A1 did? Probably be easier just to buy a military jeep.
     
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  10. Jul 1, 2019
    garage gnome

    garage gnome Rust polisher Sponsor

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    If I'm that deep, its probably someplace I don't want to be. The deepest I'm comfortable with is up to the floors.
     
  11. Jul 2, 2019
    duffer

    duffer Rodent Power Sponsor 2019 Sponsor

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    If you axles, transmission, transfercase are all sporting high terminated vent lines, I think the only thing that you are going to accomplish by pressurizing is the increased time spent replacing the seals. Those vent lines have already eliminated the negative pressure associated with rapid cooling. Floor level water depth is way different than completely submerged. On my B, I terminated the vent lines just below the hood and made filter caps for them that should "air lock" if they do get a short, intermittent submergence. They are similar to the vent on my York but with a hose connection instead of the o-ring fitting:
    [​IMG]

    [​IMG]
     
  12. Jul 5, 2019
    Keys5a

    Keys5a Sponsor Sponsor

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    If you were to pressurize your axles and trans/xfer case, I would regulate them to no more than 1 psi. I think even this might push gear oil out the various seals depending on how the vents are regulated.
    I have had great luck just running vent lines up to the cowl under the windshield.
    -Donny
     
  13. Jul 5, 2019
    PeteL

    PeteL Member Sponsor 2019 Sponsor

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    The military Fording system is controlled by a manual valve, to be pressurized only while in the water.
     
  14. Jul 7, 2019
    Bill F

    Bill F Finally running

    Hillsboro NH
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    The m38 didnt pressurize the axles. Only the transmission and transfer cas . The axles had a one way vent on them
     

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