89 burb: does 4x4 = posi rear end?

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by Big6ft6, Jan 17, 2008.

  1. Big6ft6

    Big6ft6 Rockstar 100 Posts

    Hi I have a 1989 suburban 2500 4x4 with manual lock out front hubs. My question is, when I shift into 4x4 does that lock the front and rear axles into posi-traction?
  2. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    Shifting into 4wd only locks the transfer case. The differentials operate completely independently. I doubt there's any kind of traction aid in the front diff, unless you've put it there, because OEM's don't like to put traction aids up front at the factory. Rear may have a traction aid or may not. G80 is the usual RPO code to look for, but I don't know if that will refer to the Eaton Gov-Lock or a clutch type LSD in your year.
  3. Big6ft6

    Big6ft6 Rockstar 100 Posts

    Thanks MrShorty

    I noticed while crawling under the truck that there is a cable that goes to a lever sticking off of the rear pumpkin. I thought maybe that was linked to a diff lock or something that activated when in four-wheel-drive. From your response it sounds like it is possible the rear has a locking device, but for sure the front would have an open differential?

    I always thought that the rason they didn't want you to drive on dry pavement in 4x4 is becuase all the differentials are locked?

    So without a traction device up front, in most slippery situation (like mud) you really end up with 3 wheel drive if one of the front wheels starts spinning since there is an open differential up front?

    Also where would I find the RPO code? Is that on the rear axle?

    thanks for the insight!!
  4. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    When you open up the glovebox, there should be a fairly large sticker there with a whole ton of incomprehensible numbers and letters. Those are your RPO codes. If you decode those RPO codes, you will find out pretty much every single option, nuance, and otherwise about the truck when it left the factory, right down to the original colors.
  5. Big6ft6

    Big6ft6 Rockstar 100 Posts

    Thanks Crawdaddy! Now I know what I'm going to do as soon as I get home. Find out what treasures are lurking in that $500 hunk of smoking metal! (hopefully the smoke will go away when I get the new engine in!)
  6. AdvSwede

    AdvSwede New Member

    OK, I'm learning about my truck. I checked the RPO codes and have GQ1, GU6, G80. Does that mean I have open diff in front, 3:42 gears, Posi in the rear?

    '93, 1500, Burb, 5.7, 4x4

    Found a link to this website on another posting


    Researched my RPO and this it what I found

    GQ1- Open Diff
    GU6- 3:42 gears
    G80- posi traction/locking diff
    Z82- Trailering equip'd
    M30- 4L60E, 4-Speed Auto
    L05- v-8, 5.7, TBI
    Last edited: Jan 13, 2013
  7. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    Try this: http://www.rpocodes.com/

    Looks like you were editing while I was posting. I like that site, they seem to keep it updated. Good luck
    Last edited: Jan 13, 2013
  8. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Yes it does, providing it hasnt been swapped out over the years.
  9. AdvSwede

    AdvSwede New Member

    Thanks RayVoy

    - - - Updated - - -


    I guess I can see what happens in the snow when I get the Master Cylinder fixed. Thanks
  10. Boonduff

    Boonduff Rockstar 4 Years 100 Posts

    I believe what you saw was the brake bias lever. It adjusts the brake pressure by sensing how much the suspension compresses from a heavy load.

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