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  • 87 1/2 ton getting posi traction/limited slip questions

    truck is an 87 1/2 ton swb. right now only one wheel turns. im not sure if its an open rear or if the posi unit is not working. if it is an open rear end would i need to buy another rear end and put it in to get both wheels turning or can you make a open rear a posi by installing say an eaton posi unit? its just a 2 wheel drive daily driver, I just want to have a little better traction this winter. thanks for the help guys

  • #2
    Re: 87 1/2 ton getting posi traction/limited slip questions

    Did the third gens have posi? And what do you mean one wheel turns? Does the other drag along behind the truck when moving, or is this a problem with the rear suspended and turning the input by hand?
    1999 Chevrolet K2500, Crew Cab, Short Box, 4L80E, 454 ci, 3.73 rear 14b FF 10.5"
    Working on my own custom tune with EFI Live.

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    • #3
      Re: 87 1/2 ton getting posi traction/limited slip questions

      no the truck runs and drives fine. only one wheel(axle) is powered. I have no idea if the third gens had posi's. if now what kind of truck or car should i look at getting a rear end out of. I guess i just want to know the easies/cheapest way to get a posi in this truck...
      s

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      • #4
        Re: 87 1/2 ton getting posi traction/limited slip questions

        Yes the older trucks had gov bombs just like 88 and up. The Gov Bomb has been around since 1973 actually, making the last trucks to actually have what you would call a "posi" the 67-72's. This is talking about the GM corporate rear ends of course.

        Okay easiest and cheapest is probably finding a truck equipped with a factory gov lock ( or something someone has rebuilt along the way and is selling) and swapping diffs. The gov lock ( or gov bomb) is a weak design and it will fail, especially in the 10 bolt. It's the nature of it's own design, attempting to be a locker than any joe blow can drive with.

        Here's a demo on the components and operation of an Eaton Gov lock if you care to look.

        http://www.youtube.com/watch?v=tTGZOJQQBeE

        If your 87 had a gov lock originally you need to find your RPO code sticker in the glove box and take a look. The code is G80. Your rear end ratio will be a G something too, like GU1, GU2, GU3 and so on. Doubtful you are any deeper than 3.42 ( GU6) because 3.73 is GT4 and 4.10 is GT5. Do you want the same gear ratio as you have now as well? You haven't mentioned that so I may as well ask. Finding another pickup truck in your era with deeper gears and a gov lock would be difficult. About the only easy factory application would be a 1/2 ton Suburban. Pretty much any half ton rear from 73-87 trucks and then the 73-91 2 wheel drive Blazers and Suburbans fit.

        So reall you have the junk yard option or rebuilding your diff. Junkyard will be cheaper but then you might get something that is junk as well ( even if warrantied it still takes your time to repair). The other is to add an LSD ( limited slip) to your existing rear end. I would never add a gov bomb, but something like an Eaton clutch pack LSD( my personal daily driver fav) or even a Truetrack would be a nice upgrade. That of course will most likely cost more but then you know what you have.
        JUST FOR CLARIFICATION

        I hate GMT900 trucks period.

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        • #5
          Re: 87 1/2 ton getting posi traction/limited slip questions

          ETN-19557-010, this what i would get, if you dont regear you dont have to reset your shims. its a pretty easy install.

          the only way to make a gov lock last is to stay out of the throttle, I have one in my yukon.

          i have the eaton in my firebird that sees track abuse and its lasted just fine.
          04 Avalanche Z71
          87 Firebird, 07 Monte Carlo lt, 08 lucerne cxl
          some previous; 99 GMC Yukon SLE, 89 350/5spd, 04 550 cclwb, 03 2500hd ccsb, 06 2500hd eclb, 03 sclb 2500hd

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          • #6
            Re: 87 1/2 ton getting posi traction/limited slip questions

            the codes are gu4 which i think is 3.08, staying with that is fine and going higher to 3.42 or so would also work for me. other is g50 and im guessing thats non posi code for rear end. if i bought something like the eaton posi does that go in the rear end i have now or do you have to have a rear end that was originally a posi?

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            • #7
              Re: 87 1/2 ton getting posi traction/limited slip questions

              You can get a detroit true trac, gears, and a complete overhaul kit for 600 or just under. I think that is the best route.
              Originally posted by Xander Berkeley
              I'd better make hay while the sun shines.

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              • #8
                Re: 87 1/2 ton getting posi traction/limited slip questions

                Originally posted by chornet44 View Post
                the codes are gu4 which i think is 3.08, staying with that is fine and going higher to 3.42 or so would also work for me. other is g50 and im guessing thats non posi code for rear end. if i bought something like the eaton posi does that go in the rear end i have now or do you have to have a rear end that was originally a posi?
                The housing is unimportant, they are the same no matter what gear set and carrier were in them. If you are fine with the 3.08's just buy an 8.5" 28 spline limited slip carrier of your choice. I don't personally like the torque biasing style truetrac myself and prefer the simplicity of the clutch pack LSD. The choice is up to you. All you need are carrier bearings and a limited slip.
                JUST FOR CLARIFICATION

                I hate GMT900 trucks period.

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                • #9
                  Re: 87 1/2 ton getting posi traction/limited slip questions

                  ok thanks, thats what i needed to know. there is a 90 model suburban being parted out here, do all those suburbans have posi's?

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                  • #10
                    Re: 87 1/2 ton getting posi traction/limited slip questions

                    im sure it was an option, and they have 30 spline axles so you cant just take the govloc and put it in your truck. even if you found the right one for your axle you would have to baby it to make it live. thats why most just get the aftermarket posi or locker and put it in they're axle and call it a day.
                    04 Avalanche Z71
                    87 Firebird, 07 Monte Carlo lt, 08 lucerne cxl
                    some previous; 99 GMC Yukon SLE, 89 350/5spd, 04 550 cclwb, 03 2500hd ccsb, 06 2500hd eclb, 03 sclb 2500hd

                    Comment

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