Finding the right posi-traction differential for my 1990 Silverado 2X4 ?

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by JTward1, Dec 28, 2012.

  1. JTward1

    JTward1 Rockstar 100 Posts

    I'm on the prowl for a GM posi-Traction differential to put in my restored 1990 Silverado 1/2 ton. It has a 305 ci engine. A rebuilt 700R4 trans and the standard differential with 3:42 gears. When ever i go looking for a rear end there are 28 spline or 31 spline and some info about the rear end, but I don't understand what I'm looking at. Me I don't know one if it bit me. In the glove box is the RPO codes, I looked them all down and some make sense and my truck has one C5G=GVW rating of 5600 Lbs. and codeGU6 Rear axle, 3:42 gears Which i want to keep. Am I correct that with the right posi differential I'd only have to change the ring gear, because the pinion gear stays right where it is, or do I need to get the entire differential built by a shop ? That's the only information I have to go hunting for a Posi-Traction differential. Any advice is most appreciated. Thank you ! :great:
  2. Jacqson

    Jacqson Rockstar 100 Posts

    The Posi traction/Locker unit is a complete carrier so you simply put the old ring gear on the new carrier and reuse the existing pinion gear. It is also advisable to replace the carrier and pinion bearings as well. Are you looking for a locker, selectable locker or limited slip. There's lots of Posi traction type units out there, it's just a matter of what will work best for your application and use.
  3. JTward1

    JTward1 Rockstar 100 Posts

    Thank you, Eaton has a few new differentials and I'm drawn to the posi-trac over the "dura-trac" unit as it hasn't been around that long and the Posi-trac costs the same, so I'm sticking to what i know. Found a brand one one the auction site for $411.00. Sounds just right for my application. I'm a little scared that it can be installed without a problem.
    Last edited: Feb 21, 2013
  4. Jacqson

    Jacqson Rockstar 100 Posts

    Don't worry about an installation problem. If the unit you buy is the correct one for your application any reputable differential shop can install it for you without giving you any headaches, at least until you see the bill. :lol:

  5. JTward1

    JTward1 Rockstar 100 Posts

    Thank you !

    - - - Updated - - -

    How do I tell if it is a 10 OR 12 bolt rear? Count the bolts in the rear cover? and how do I tell if my differential is a 28 or 30 spline ? Thank you !
  6. Jacqson

    Jacqson Rockstar 100 Posts

    Yeah, count the number of bolts on the rear cover and as far as whether it's a 28 or 31 spline pinion, I'd just go down to your local dealer and give them the RPO Code(GU6) and they should be able to tell you which spline count you have in the diff.

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