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Fluids on a 99 GMC SIERRA Z71 NBS

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by Jeff Dodson, Nov 15, 2013.

  1. Jeff Dodson

    Jeff Dodson Member

    I am fixing to change the rear, front differentials and the transfer case. I know someone has told me on here but I cannot find it and the PO still has not found the owners manual. But can y'all tell me what I need in these. I like ROYAL PURPLE, tried and proven in my HARLEY DAVIDSON... So I would really like to use that...... But I need to know weights .... And how much so I can buy enough of what I need. Truck has 250k, so I don't think they have been changed, maybe the transfer case but not sure. PIECE OF MIND !!!!!!

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    I know someone told me this info on another post but I cannot find it and would really like to change the fluids today but don't want to put anything in that I'm not suppose to
  2. j cat

    j cat Active Member 1000 Posts

    the amsoil web site has all this info . look here ; http://www.amsoil.com/mygarage/vehiclelookup.aspx?url2=1999 CHEVROLET TRUCKS SILVERADO 1500 PICKUP T

    now you must know what rear diff you have so be sure to check the glove box code list.

    my 2000 silverado uses 75-90 wt synthetic gear oil rear locking diff eaton. the front diff uses 80-90 wt GL5 gear oil. the transfercase uses trac II transfercase fluid. transmission I have used mobil synthetic transmission fluid since 2001. this is pre dexronVI which is now the GM approved fluid.

    I did not change to the dexron VI as the fluid I have been using will not have the damaging effects of the defective DEXRON III that GM used to recommend in their fleet of vehicles.
  3. Pikey

    Pikey Moderator Staff Member ROTM Winner 1000 Posts

    [MENTION=39185]j cat[/MENTION] are you running a friction modifier in your rear diff? if so which one? I am running the amsoil 75-90 in my diff, but get conflicting reports about using a modifier.
  4. j cat

    j cat Active Member 1000 Posts

    The friction modifier is used in my full time limited slip 1996 impala. this requires the friction modifier to reduce chatter when making turns.

    the truck with the eaton locker is just 75-90 wt synthetic.. modifier will mess it up ..these differentials are made quite different and the operation is very much not the same.

    with the truck the rear diff is not with both wheels providing traction all the time..only when one wheel rotates more than the other will the rear wheels lock together as one axle..

    with the impala the rear diff is always working as one axle . both wheels provide traction all the time..the problem with the impala diff is the wheels are not locked ,,, meaning that a force of 50 ft LBS will make them slip so that one wheel will rotate at a different speed than the other. this is where that modifier comes in to play.....
  5. Jeff Dodson

    Jeff Dodson Member

    Well I'm a ROYAL PURPLE kinda guy. Tried and tried in my Harley Davidson.... I just put the MAX GEAR in the front and MAX TRANSMISSION in (equal to the Dexron), next is the rear.... What does it hold, about 4 quarts ??????
  6. 99'HEARTBEAT

    99'HEARTBEAT Moderator Staff Member ROTM Winner Platinum Contributor 1000 Posts

    Jeff...buy 3-Quarts, as the 10-Bolt Rear Diffs takes about 2-1/2 quarts to fill.

  7. j cat

    j cat Active Member 1000 Posts

    the amsoil site I listed here has all that info... amounts and the proper fluids.
  8. Jeff Dodson

    Jeff Dodson Member

    Yea I read that, was just posting what I had done. 80 bucks on 2 for the front and 2 for the Tcase , damn RP is expensive
  9. j cat

    j cat Active Member 1000 Posts

    the royal purple is expensive ..
  10. Jeff Dodson

    Jeff Dodson Member

    Not much more than any other SYN OIL... Besides that, ITS THE BEST and this truck has 250 k and I want it to last longer

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