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Rear Axle Question

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by nofeartruckin00, Oct 11, 2001.

  1. nofeartruckin00

    nofeartruckin00 1/2 ton status

    Oct 5, 2001
    Likes Received:
    Germantown, Wisconsin
    First, just wanna say thanks to all the people who helped with my auto/manual hub question. Got the warns in today in 25 minutes, work great! I've got a '91 Jimmy with a 350/4L60E/NP241/corp 10 bolts, and wanted to know if any of these came with posi in the rear. Both tires always put power to the ground, and was wondering if this came from chevy or if the previous owner put in an aftermarket limited slip. And does anyone know what my gearing would be in the axles, 3.73??? Thanks alot.

    Mud, the ultimate paint job
  2. Can Can

    Can Can Pusher Man Staff Member Super Moderator

    Feb 17, 2000
    Likes Received:
    Cochrane, Alberta, Canada
    Do you by any chance still have the RPO code sticker somewhere on the truck(either in the glovebox or on the driver's side fender well in the engine compartment)? If it's there, it might have the codes to help you figure this stuff out.

    Let me know and I can decipher the codes for you.....

    <font color=blue> NEVER FORGET, NEVER FORGIVE, NEVER SURRENDER<font color=blue>
  3. CaptCrunch

    CaptCrunch 1/2 ton status

    Feb 2, 2001
    Likes Received:
    I believe 3.08,3.42, and 3.73's were all options for these trucks. The best way to find the gear ratio is find the RPO sticker and match up the code or just pull the cover and count the teeth on the ring and dived it by the # of teeth on the pinion. Also if you jack up the rear of the truck and try and spin the wheels... a posi or locker won't spin... an open diff will spin usually.

    1987 Chevy K5 Blazer- 350 TBI
    <a target="_blank" href=http://coloradok5.com/gallery/captcrunch>http://coloradok5.com/gallery/captcrunch</a>
  4. Blue85

    Blue85 Troll Premium Member

    Jul 26, 2000
    Likes Received:
    Grand Rapids area
    Yes, but if it is a factory posi, it is a gov lock and that will seem just like an open diff for this test. The the gov-lock (called LSD or posi) option would be listed on the RPO sticker. If you actually were going to pop the cover (and just call it maintainance and change the gear oil while you're in there) it would be easy to tell which kind of differential you have.

    Or, just put one wheel up on a jack and hit the gas, if the truck shoots through the back wall of your garage, it has a locker. [​IMG] (No, please don't actually do this)

    <font color=green>Does a Dyslexic Insomniac Athiest lay awake at night wondering if there's really a Dog?</font color=green>
  5. txbartman

    txbartman 1/2 ton status

    Jun 1, 2001
    Likes Received:
    Plano, TX
    There have been all sorts of opinions mentioned on this site (seems like every week) about how to tell if you have a posi or locker or open as well as a whole variety of ways to figure out your gear ratio. But, the best way to do both of these things BY FAR, is to simply pop the cover off and look. Many gears are stamped with their ratio. Some are not.

    For the ones that aren't, you will count the teeth on the large gear (the ring gear, it is parallel with the frame and perpendicular to the axleshafts and "linked" to the shafts) and divide that number by the number of teeth on the pinion gear (small gear on the front of the axle connected to the driveshaft).

    When opening the rear end up, you will also be able to tell if you have some sort of locking mechanism or simply an open diff. Many guys here can help you decipher which is which based on what you see. I couldn't tell you what a posi looks like, but a full locker is obvious as well as an open diff. If you haven't ever been in the rear end (of the truck...LOL), it would be a good thing to do anyway. All it would take is the time to jack up the rear end (10 minutes, including getting the jack and stands), remove 10 bolts (5 minutes?), drain the oil (5 minutes), then pull the cover. Spend 20-30 minutes looking through the diff, checking everything out, counting and recounting. Then clean it out, including any gasket stuff off the cover (10 minutes). Put the gasket in place, return teh cover, insert the 10 bolts (5 minutes). Add 2.5 quarts of 80W-90 high quality synthetic gear oil (5 minutes). Now you KNOW for sure and know some more about your diff including its condition.

    So, what is that, an hour? You could probably spend more time in the bathroom with the latest copy of Four Wheeler!

    In my opinion, it is the best preventative maintenance and knowledge gathering activity you can do. IMO

    Check out <a target="_blank" href=http://tx85gmcguy.alloffroad.com>My Jimmy</a> with all her projects!

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