Milky Gray Differential Fluid

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by TheBaron97, Jun 27, 2020.

  1. Colt6920

    Colt6920 Light Load Member

    Apr 28, 2017
    The advice about not changing trans fluid only applies to cluch/band based automotive automatic transmissions. What happens if you do not change it for a couple hundred thousand miles is the friction material ends up in the fluid, and this still allows it to somewhat work until you put new fluid in. However, at this point, the transmission is already on borrowed time, the old fluid is just masking the issue. And, if you change the fluid regularly, this should not become an issue in the first place, and is the best option. I do 50k intervals on my personal pickup.

    But, like I said, this only applies to the light duty automatics found in cars and pickups, and beat up ones at that. The only heavy duty trans this may somewhat apply to is the Allison autos. But otherwise, differentials, transfer cases, and manual transmissions (and automated manuals) in any vehicle, from a car to a semi, will only benefit from an oil change (provided the right fluid is used).

    In your case, milky fluid means water ingress. Change it ASAP, this milky fluid sucks at lubrication and will cause rust. I would also change the gasket on the diff (or use RTV) and check the vent/ breather tube on the diff, maybe add a longer tube if you go into water often. Also, I would regrease U-joints and other chassis components (if they are greasable) and check the trans and motor oil as well for water.
    Rideandrepair and TheBaron97 Thank this.
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  3. TheBaron97

    TheBaron97 Light Load Member

    Jun 22, 2020
    Williston, North Dakota
    Good deal, there are a lot of welds on the top of the differential housing. I wonder if the housing is all messed up in the inside and if the seals are leaking. It's going to be a big job to take it all apart but probably worth it. Luckily I just bought a new jack.
  4. SmallPackage

    SmallPackage Road Train Member

    Dec 20, 2019
    Marion Texas
    If they are Eaton rears check them for cracks at the welds where the spring perches are. They have a knack for cracking. Water may get in from there.
  5. BoxCarKidd

    BoxCarKidd Road Train Member

    Aug 26, 2014
    Rears use 75W-90 syn.
    Your truck should have plugs in the side of the hubs where the axle shafts bolt in. AIso remove those and drain that oil out the bottom also. Put a quart back in each one.
    Axle vents are not missing?
    I would change the oil and run it, their tough. Check the front hubs as well.
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