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g80 differiental fluid

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by Gooseberry09, Oct 11, 2013.

  1. Gooseberry09

    Gooseberry09 New Member

    can anyone tell me what kind of fluid that i need to put into this? i dont have the service manual and a few people have told me different things such as getting the additive to put in it and others have told me regular fluid will work. any ideas guys? thanks in advance
  2. 99'HEARTBEAT

    99'HEARTBEAT Moderator Staff Member Platinum Contributor 1000 Posts 100 Posts


    The Below Information is from G.M.

    SUBJECT: LOCKING DIFFERENTIAL (G80) LUBRICANT - (SERVICE INFORMATION) VEHICLES AFFECTED: ALL LIGHT TRUCKS EQUIPPED WITH G80 REAR AXLE ALL YEARS

    ***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.


    GM....recommends the following Lubrication in the Trucks with Locking Differentials: Synthetic 75 W90; GM Part # 9986115


    Edit:....I'm running in my Rear Axle Royal Purple 75/90W Gear Lube.
    Last edited: Oct 12, 2013
  3. j cat

    j cat Active Member 1000 Posts 100 Posts

    I use mobil synthetic gear lube 75-90 wt. this is all that is required. no additives with these eaton locking differentials.

    the fill hole should have a tag indicating this .I never drain the rear diff with out removal of the rear cover and using mineral spirits cleaning the diff box out and magnet. then inspect the gear teeth for cracks etc...

    make sure the vehicle is level when you top off the fill. should be 1/2 inch from the top ...if you put too much in no big deal. at worst it will come out the venting hose which should be checked for restrictions.

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