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  1. #1

    Default Is it OK to put synthetic gear oil in my front differential?

    I drained my front and rear differentials (100k miles) and refilled each with Mobil 1, 75-90w.

    I looked around on-line and found a Chevy booklet. It said that it's alright to use synth in the rear, but didn't say if it was alright for the front.

    Is it?

  2. #2

    Join Date
    Feb 2008
    Red Wing, Minnesota, United States


    my only thought is that maybe because it sits for so long and actually isnt moving around like the rear all the time that it needs something heavy to keep it properly lubed for when you finally do through it into 4WD
    99 K1500 Suburban LT "THE BEAST"
    Hypertech III, K&N, true dual

  3. #3


    Quote Originally Posted by vncj96 View Post
    ...that it needs something heavy to keep it properly lubed for when you finally do through it into 4WD
    So dinosaur gear oil is heavier than synthetic? I've never heard that before. The front specs say 80-90w and the rear 75-90w. Autozone's computer said 75-90w in both. Since I couldn't find any 80-90w for the front, I just used the 75-90w figuring it would be alright.

  4. #4


    yes you can add syn oil in the front diff---the only issue is the diff if it has a LS (Limited Slip) you need the friction modifier.......mike
    Michael Collins
    1993 4X4 Suburban
    many other toys as well

  5. #5


    How do I check to see if has LSD? On my sports car you jack up the back and spin the tires. When both move you have LSD. How do you check it on a 4x4 burb?

  6. #6


    look at the spec tag on the door jam and or glovebox. you can do the same test you said to see and the fail safe method pull the rear cover and look. you are going to replace the oil anyway......mike

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