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Cat 740 transfer case oil in front diff

Discussion in 'Other Earthmoving Equipment' started by cb75, Aug 9, 2017.

  1. cb75

    cb75 Well-Known Member

    Joined:
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    Location:
    The Bluegrass State
    Hey Guys, hoping someone could point me in the right direction. Working on a Caterpillar 740 ADT S/N AXM00773 with approximately 13k hours on it. Oil is leaking from the breather for the front axle housing. I'm guessing the Oil is coming from the transfer case and getting in the front axle when the diff lock is activated. Does this make sense? I will not have access to SIS or a service Manual until sometime tomorrow and was just trying to get a head start.
    I've never worked on this particular system on these trucks. Was told of the oil leaking from the breather and that the transfer case is using oil abnormally.
    Thanks for any guidance ya'll may be able to provide.
     
  2. Cmark

    Cmark Senior Member

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    Jan 2, 2009
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    1,526
    Location:
    Australia
    Yes, that makes sense. The oil pressure for the diff locks is supplied by the output transfer gear pump. If it's transferring oil from the OTG case into an axle, you have something leaking in the diff lock mechanism.
    Also be aware that the OTG has quite a small oil capacity and if it's allowed to run dry, it'll self destruct fairly quickly.
     
    mrappels and mikebramel like this.
  3. cb75

    cb75 Well-Known Member

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    Location:
    The Bluegrass State
    Thanks for the reply Cmark. We capped the line for now so the truck can be used while we have another 740 in the shop for brake repair.

    I guess the front diff will need to come out in order make permanent repairs? I've never been into the differentials on these trucks, only the old D400D models.
     
  4. Cmark

    Cmark Senior Member

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    Yes, you'll have to remove the front axle to get the diff out. It's easier to take out the axle and A-frame complete but you will need a special puller to get the A-frame free from the tapered pin.
     
  5. cb75

    cb75 Well-Known Member

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    Location:
    The Bluegrass State
    That's what I was afraid of. If nothing else at least we'll get to restock our cribbing lumber supply.
    This truck also needs a suspension cylinder resealed so we can get that taken care of while we're in there.

    Thanks for taking the time to read my post and respond. Sounds as tho you've been into the diffs on these trucks before?
    Reason I ask is because on a different truck (another 740) we changed the oil in the front diff and had a dowel pin come out with the drain plug magnet. Haven't had any other problems with that differential and no bad sample results. We may just have to get good at removing axle housings!
     
  6. mrappels

    mrappels Active Member

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    Nov 30, 2015
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    Occupation:
    Diesel Plant Fitter
    Location:
    Zimbabwe
    Hi cb75, that special puller is just a metal plate with threads and a studded bar that you can screw. can be done in a machine shop. it bolts on to where the cover is for the front axle a-frame pin, You could always use the cat tool.. but its a pretty penny, and those pins can be really stubborn sometimes...

    Oh, and it is definitely easier working on those axles outside of the machine like mark says.

    Btw, if you have internet access, Caterpillar's online parts website, parts.cat.com, is REALLY useful checking out what goes where.. especially when the SIS isn't handy.

    I would be very worried about a dowel pin just "falling out".. how many hours has it done? and there was nothing else on the plug? its hard to imagine it just dropping out, may indicate something coming loose?..


    BTW, would love to see what went wrong on that truck with the brake problems.. never seen the brakes actually fail apart from that inner duocone.. and the final drive bearings