HOW TO: Change your front/rear diff oils

Discussion in 'How To' started by jeepkj02, May 6, 2006.

  1. theroofable

    theroofable Full Access Member

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    Just verifying that I can use the 85w-140 in the front and the rear? If so Im off to buy 1 gal of it on tuesday, and hopefully get it changed before the weekend!
     
  2. 67Customs

    67Customs Full Access Member

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    I've read that a few times and I've done a lot of research on it.

    However, that still doesn't explain to me why in my owners manual they specifically say to use 75W-140 in the front. They apparently thought it to be better at the time of that publication but thought 80W-90 to be good when writing the FSM.

    Will my Dana 30a blow up because I use 85W-140? Probably not. I just want to know why they can't get it straight and if 75W-140 is better for my Dana 30a.

    In all honesty, I'm most likely going to run Valvoline DuraBlend 85W-140 during my next change. Split the difference. But, she has already ran 60K miles on a couple of changes of Mobil 1 75W-140 front and back with zero problems.
     
  3. TwoBobsKJ

    TwoBobsKJ Full Access Member

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    In my opinion the Owner's Manual is as much marketing as information - and that's verified by the fact that the fluids referenced are always "Mopar-brand" so-and-so. With the 75W-140 Chrysler is pushing the more expensive product. But the FSM is for the mechanics who actually work on the vehicle and they are advised to use the stuff that will work well. In this case it is dino oil vs synth.

    I think your choice is a good one (DuraBlend.) Gives you peace of mind and will do a good job in your diffs. :happy107:

    Bob
     
  4. Moon

    Moon Full Access Member

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    I got the diff oil changed in the hooptie last friday. The only tip that I would mention (besides the ones already posted), is: DO NOT let the old gear-oil get into your car. It smells like so much nasty-ass, and doesn't seem to want to go away on its own. I had a rag with a little bit of the old oil on it. I threw it out the window while driving down the road, but the awful smell remains. :(

    :cheers:
     
  5. tjkj2002

    tjkj2002 Full Access Member

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    Try doing the front diff in a Cat 621B,55 gallons of 80w-90,that's one big drain pan.
     
  6. first&lastKJ

    first&lastKJ Full Access Member

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    I have an 02 and 07 KJ does anyone know what gear lube came in them from the factory.
     
  7. TwoBobsKJ

    TwoBobsKJ Full Access Member

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    Do they have the towing package? Do they have TracLok?

    That determines what was in the rear diff from the factory...

    Bob
     
  8. first&lastKJ

    first&lastKJ Full Access Member

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    No, and No.
     
  9. TwoBobsKJ

    TwoBobsKJ Full Access Member

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    They most likely used the 75W-90 synth. But you can put in 85W-140 dino in both front and rear diffs.

    Bob
     
  10. first&lastKJ

    first&lastKJ Full Access Member

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    Thanks. I think i'll go with the 75w-140 synthetic front and rear in both of our KJ's.
     
    Last edited: Jan 10, 2012
  11. sevenhelmet

    sevenhelmet Full Access Member

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    I'm now using 80W-90 front and rear and I've put over 100 miles on it since the change with no problems.
     
  12. mdmaroon

    mdmaroon Full Access Member

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    One thing: Take the fill plug out FIRST. If you take out the drain plug, and then for some reason can't get the fill plug out, then you aren't going anywhere until you do get it out, one way or another. Maybe you'll need a tow truck to take you to a shop...

    I know it's not too likely that this will happen, but at least if you take the fill plug out first, you know you'll be able to get fluid in, assuming everything is okay with the drain plug. If you can't drain it, then you just put the fill plug back and you can still drive.
     
    Last edited: Jan 22, 2012
  13. Squeeto

    Squeeto New Member

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    I like this way as well. But it causes the diff to point up not hang down. If the oil level needs to be 1cm below the fill hole we aren't accomplishing this by filling until the oil drips out.

    I figure that some fluid can be sucked out but how important is this oil level? It looks like the bottom of the axle (thus seals) is below the proper oil level anyway.

    ________

    So I must jack the front to get under the truck for the front diff. If I let the axle hang it actually points down even if the front of the truck is elevated?


    Sorry for being so cautious about this. This is the first vehicle I have owned that requires the level to be below the fill.
     
  14. Squeeto

    Squeeto New Member

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    Okay, I tried this on the rear axle and it does work:

    [​IMG]

    String to diff cover:
    level = 1 13/16 inch
    hanging = 1 15/16 inch

    I don't think that this trick works on the front though.
     
  15. theroofable

    theroofable Full Access Member

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    Im pretty sure its meant to be 1cm below the top of the fill hole. Therefore, it needs to be jacked up so that when it oozes out, but when level again, it would be above the fill plug.
    When i did it, I used a giant syringe, and pumped the required amount of fluid into each diff. This is one way to ensure the proper level.
     
  16. sevenhelmet

    sevenhelmet Full Access Member

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    I used a gallon fluid pump for mine and had no problems. Just watch out for the little plastic "wingtip" on the fill nozzle of some of them. The little plastic tips can break off inside a gearbox if you aren't careful.

    x2 on carefully taking out the fill plug first. One stripped head or torn piece of plastic can ruin your whole day.
     
  17. Squeeto

    Squeeto New Member

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    I use this:
    [​IMG]

    It's slow but mess free.
     
  18. tjkj2002

    tjkj2002 Full Access Member

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    Just fill till the bottom of the fill hole,no issues will result.

    Want a fun diff to fill try a RockJock60 as the cover is laid out at 60 degrees.If I fill to the fill hole I'll blow every seal,I have to add exactly 2.75qts.
     
  19. Squeeto

    Squeeto New Member

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    This is the 3rd gear oil change that I have done on this truck. Each time I stuck a finger in to try and guess the depth down a cm. Next time I will do as you all say.

    Thanks.

    I suppose the minds at Jeep don't want the seals to sit in gear oil 24/7 and the extra 1cm was for those of us who park on hills, curbs, the neighbors bike, etc.
     
  20. tjkj2002

    tjkj2002 Full Access Member

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    The reason is the back fill plug is rubber,just pops in/out.If filled to the bottom of the fill hole it may or maynot weep a little gear oil.

    The seals are there to seal,does not matter if they are in constant contact with the oil.No oil touching the seals means no oil in the bearings.