Determining axles in my 1990 Chevrolet 1500 ?

Discussion in 'Chevy C/K Truck Forum' started by JTWard, Jul 10, 2013.

  1. JTWard

    JTWard Rockstar 3 Years 500 Posts

    I'm not sure if I asked this already. But I'd like to put a limited slip differential in my otherwise stock and restored 1990 Silverado, It is a 10 bolt rear but I don't know how to figure out if it's a 28 or a 30 spline rear. Everyone I have contacted says I need to pull an axle and count the splines ? That's a job I'd like to do once I already have a posi-traction unit ready on the floor and ready to be installed. Just don't know a way around this problem ? :neutral:
  2. mfleetwood

    mfleetwood Epic Member 5+ Years ROTM Winner 5000 Posts

    Based on what this used parts website states, your 1990 10 bolt has 30. Check out the site and if you still are unsure, they give their phone # and email address if you need additional help. I've never seen spline count listed as an RPO code (but am not positive it's not), so you may want to check there....however, you may end up counting them just to be sure.

    Here is the explanation from the site:
    [TABLE="width: 100%"]
    [TD="align: center"]The 10 Bolt rear end with an 8.5" Ring Gear. These are basically the same internally 2WD or 4WD...Even the 10 Bolt front ends are the same "Guts"! The BEST ones are the '89 to '91 Blazer & Suburban ones or '88 and newer Pick-up trucks. These have the BIGGER 30 Spline Axles and not the 28 Splines axles. These units come in 5 & 6 Lug axles and 8 Lug for Front Differentials.[/TD]
  3. JTWard

    JTWard Rockstar 3 Years 500 Posts

    Thank you, They seem pretty sure it's a 30 spline axles?
  4. mfleetwood

    mfleetwood Epic Member 5+ Years ROTM Winner 5000 Posts

    They seem pretty confident....but you still may want to look into further and/or wait for others to respond. We have some very knowledgeable powertrain members here and I'm sure a couple of them will respond shortly.
  5. RayVoy

    RayVoy Epic Member 5+ Years 5000 Posts

    [MENTION=61229]JTWard[/MENTION], if I was you, I'd look for a used G80 rear axle from a GM full-size. Match the gear ratio you want/need and bolt it in.

    The G80 will give you posi as well as a centrifugal locker.
  6. JTWard

    JTWard Rockstar 3 Years 500 Posts

    Hay Ray, I was searching for an answer as I plan on buying a rebuilt posi-traction unit for my 1990 Silverado, but I'm a little afraid that if I purchase one, then it's shipped to me and we pull the axels and it turns out to be a 28 spline, we have to put everything back together and return and reorder. I'm kinda of looking for a safer way to find out what axels I have. It is a 10 bolt, but both a 30 spline and the 28 spline have 10 bolt covers.
    Last edited: Jul 11, 2013
  7. Crawdaddy

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

    Personally, if I were going to keep the 10-bolt and put a posi in it, I'd order the 30-spline one and if the axle shafts aren't 30-spline, swap them for the 30 spline. Stock axleshafts are pretty affordable and the 30-spline ones should be stronger.
  8. JTWard

    JTWard Rockstar 3 Years 500 Posts

    Ok, Yeah that's another way. Thank you !
  9. Sirwriter

    Sirwriter New Member

    If you're sure it's stock then 1990 stock 10 bolts came with 30 spline. Only the 1988 10 bolt came stock with a 28. By the way, will give you most of the info you can need. Have a look sometime.
  10. JTWard

    JTWard Rockstar 3 Years 500 Posts

    Well I'm not positive. I have poured over "Randy's Ring & Pinion" and they list it as both a 28 & 30, but if you squirrel down the lists you come to the 28 spline as being in a stock C1500 1990 2WD. Then there's the type of differential, 1. Yukon Dura-Grip, 2. Detroit Locker 3. Eaton Posi-traction and 4. True-Trac limited slip ? There are customer reviews, and to tell you the truth, not one of them were real great response's, the Yuko dura-grip was Ok if you added twice the amount of limited ship oil, the Detroit locker was noisy and didn't give very good traction in sand or mud. The other Eaton was out of my price range @ $1000.00 and had no reviews and that left 5. the True-Trac limited slip. It only got one review and it was positive and it doesn't need any limited slip oil, only regular gear oil. Now there wasn't enough real customer reviews to get any real time experiences, but it seems to me that the one differential with the most use is the Yukon Dura-grip. But of course it only worked well if you doubled up on the limited slip oil ? So . . . :neutral:

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