limited slip differential

Discussion in 'Maintenance & Upkeep' started by newcheylover, Aug 4, 2013.

  1. newcheylover

    newcheylover Member 1 Year

    I have a question about what differential oil and additives I should put in them. I have the G80 limited slip diff and don't know what additive to put In the front and back. I have 75w90 synthetic I will be putting in the back and 80w90 synthetic in the front. i also notice that in my repair manual is telling me to fill them only to about 5/8 to 1 5/8 inches. is this true or can i just fill it until the oil is even with the plug?

    99'HEARTBEAT MODERATOR Staff Member 5+ Years ROTM Winner 1000 Posts Platinum Contributor

    Regarding "I have the G80 limited slip diff and don't know what additive to put In the front and back" Below is a G.M. Service Information on Additive's with the G80

    G.M.(SERVICE INFORMATION) #91-4-109:

    The use of any Additive in Locking Rear Axles (G80) is Not Recommended. Rear axle additives are designed for use in limited slip differentials which are normally installed in cars. All Light Duty Trucks equipped with RPO G80 make use of a Locking Differential and the use of Additives will delay the engagement of the Locking mechanism and May Decrease Axle Life.

    VEHICLES/COMPONENTS INVOLVED: ------------------------- ---- Some Light Duty Trucks equipped with Locking Rear Axles, RPO G80.
    Part Number Description ----------- ------------------ 10950849 Lubricant, Rear Axle (1 litre)

    As specified in Light Duty Truck Maintenance Schedules, locking rear axle fluid drain and refill is required owner maintenance at the first engine oil change. Failure to drain and refill the rear axle as specified may contribute to a later axle chatter condition. Refer to the appropriate Light Duty Truck Maintenance Schedule or service manual, section OB, for further details on change intervals.
    Last edited: Aug 4, 2013
  3. BurbanMan

    BurbanMan Rockstar 3 Years 500 Posts

    I've always filled them to the plug with 0 issues.
    Last edited: Aug 4, 2013
  4. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    The "old school" test was to stick your baby finger into the hole, if it come out wet, there was sufficient lub.
  5. grampy

    grampy Rockstar 100 Posts

    That's the way I learned it - has worked for me for 50+ years - yes, I'm "old school"
  6. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    That's two of us [MENTION=53003]grampy[/MENTION]
  7. j cat

    j cat Epic Member 5+ Years 1000 Posts

    when the weather is warm/hot filling to the point of the gear oil flowing out the plug is OK.

    when its cold the gear oil does expand a good amount this is where you would fill to 1/2 inch below the fill plug. this is not something to be overly concerned about. I would however check after running the vehicle , to be sure it is properly filled. sometimes it will drop some after use age.[air pocket].

    with the rear diff make sure the cover is removed and the debis is cleaned with mineral spirits and a cloth.also the cover magnet. then check the gears for cracks/pits.

    if you do not remove the cover it just shortens the life of the bearing/pinion etc.
  8. stchman

    stchman Active Member 2 Years 1000 Posts

    There is a common misconception that the G80 is a limited slip differential, it is not. The G80 is a locking differential. The G80 requires no additive in the fluid.

    If you are going to change the fluid in the rear differential, simply use Mobil 1 75W-90.

    I have always filled gearboxes with a check plug until the fluid comes running out of the fill hole.
  9. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Actually stchman, there is a common misconception that the Eaton G80 is not a LSD diff. It is actually a LSD that operates as an open diff until there is a speed difference, between the axles, of 100rpm. At this point, the operation of the locking pawls turns the G80 into a posi rear-end. Granted, a posi that operates differently than a true posi rear-end, but it does have clutch packs to apply lock up torque to the axles.

    You are correct, additives do not need to be added, as long as the correct fluid is used.
  10. stchman

    stchman Active Member 2 Years 1000 Posts

    There are literally a million different opinions on what the an LSD and a ALD are. An LSD and an ALD use very different mechanisms to achieve applying power to both wheels.

    Now there are some that consider ALDs a type of LSD, but it appears that there is a LOT of opinion as to the difference between the two.

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