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M38a1 Rear Axle Wheel bearing zirks and vents

Discussion in 'Early CJ5 and CJ6 Tech' started by DanStew, Jan 21, 2014.

  1. Jan 21, 2014
    DanStew

    DanStew Incorrigible. Staff Member

    Lexington, South...
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    On the military axle there are two threaded in fittings per wheel bearing. one is a plug and the other is a spring loaded vent or grease purge. I am going to add a zirk to replace the plug, but I am debating on the vent fitting. From what i read it lets grease out and nothing in, but at its age can i trust it? It isnt rusted, but i am worried about letting water into the rear bearings. Have you guys just left the vented one alone or have you replaced it?

    tHanks!
     
  2. Jan 21, 2014
    gunner

    gunner Member

    Washington state...
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    Left it alone on my A1 and it works fine.

    Try pumping some grease in the zerk- when it's full, the vent will open and release the excess. I don't think it's a "vent" as much as it's there to let you know when you have too much grease in there. If you put too much grease in, it will get past the seals and go towards the diff, brakes, etc.

    I remember back in the day that John Compton at Border parts (this was back in the early 70s) mentioned to just give the zerk a pump or two of grease whenever it was lubed. That way, it wasn't overdone (about this time, a lot of A1s were entering civilian use- thanks to guys like John- and he was telling that to a new A1 owner in the BP shop when I was there for CJ2A parts). The cavity in there is small and can easily be overfilled since you can't see the excess coming out as you can with something like tie rods or u-joints. The vent is there to keep problems from happening. I imagine the military might have thought that a succession of 19 year old knuckleheads wrenching on the A1s might not always keep in mind that small cavity and just keep pumping in the grease until.....
     
    Last edited: Jan 21, 2014
  3. Jan 21, 2014
    PeteL

    PeteL Member 2020 Sponsor 2019 Sponsor

    Hills of NH
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    The over-pressure vent also has to do with the military waterproofing system, for snorkeling operations.
     
  4. Jan 22, 2014
    DanStew

    DanStew Incorrigible. Staff Member

    Lexington, South...
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    Thanks guys. I just cleaned the valved ones and reinstalled. I added zerks for the other holes and did away with the plugs.
     
  5. Jan 22, 2014
    Dave Deyton

    Dave Deyton Member

    Fuquay-Varina, NC
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    Oct 12, 2003
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    According to the G503 forum, they did away with the zerk fittings, because ---

    "The Grease Fittings at the backing plates were removed by an urgent MWO to reduce the tendency of drivers and mechanics from greasing the wheel bearings too frequently which contributed to grease getting onto the brake shoes. The threaded holes on top are for spring loaded pressure relief valves."
    "the Army used Chassis Grease in WWII and the more modern GAA starting in the early 50s. GAA (Grease Automotive Artillery was for chassis, wheel bearings, propeller shafts, etc. The US Army was the world'd largest fleet operator of Willys Jeeps. Same for the rear M-38A1 wheel bearings, there were grease fittings installed at the factory to grease the bearings."

    Just don't give it too much grease too often. I get a lot of info on my M38A1 rebuild and maintenance from the G503 forum.

    Dave
     
  6. Jan 22, 2014
    sterlclan

    sterlclan Member

    exploring the...
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    excess grease causes bearings to heat up and fail,confirmed this on the crusher at work with a thermal gun ,adding 1 extra pump caused temps to rise 10 to 15 degrees...this was after the boss said he wanted to see it drooling didnt think we were greasing enough,after 3 or 4 weeks of over greasing the bearings puked .
     
  7. Jan 23, 2014
    gunner

    gunner Member

    Washington state...
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    G503 has an old Army mechanic posting a lot on these things; I think I read the same thing there.

    Removal of the zerk implies having to pull the tapered hub every time you want to grease the bearings. That's a fairly big job. I think I'll ignore that MWO
     
  8. Jan 23, 2014
    Dave Deyton

    Dave Deyton Member

    Fuquay-Varina, NC
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    I think your right, I say just don't over do it. I learn a lot from his postings.


    Dave
     

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