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Converting an Open Rear End to Twin Trac?

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  • Rear Axle: Converting an Open Rear End to Twin Trac?

    I have had a 3:54 Dana 44 open rear end which came out of an Avanti sitting in my garage for well over a decade. Well, I want to build up a rear end and add Phil Harris's flanged axle kit, but would also like to have twin trac. So, my question - what is involved converting an open rear end to twin trac? I am sure it is not as easy as just dropping in the posi unit! Assuming I could put everything together, this set up (complete with the factory traction bars) would replace the 3:31 I have in my R2 Lark now, which should wake things up nicely
    Eric DeRosa


    \'63 R2 Lark
    \'60 Lark Convertible

  • #2
    Well actually it is that simple but by the time you purchase the posi, install kit and axles with the install you'll have about as much as a new 9" or equivalent. You will still have the weaker 19 spline OEM axles (still fairly strong) but not like the newer 30-31 spline axles available from Moser or Strange so if you chose the rebuild route, consider the better axles when you buy the posi.

    Posi $350 or so, bearing kit inner -$125, outer bearing kit-$100 or so, new R&P gear, if needed - $150, Axles - $300 guessing, install $150 up to give you an idea of what you are getting into.

    Hope that helps, Bob

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    • #3
      Ok after reading this over a couple times I think I figured out that you are not wanting to do the "easy" thing just swapping complete assemblies or even just swapping the whole TT carrier assy. and ring gear into the "Traction Bar" Avanti Housing.

      You want to take the TT unit from the TT, 44, 3.31 Axle Assy. and install it in the Avanti Housing keeping the Avanti's 3.54 Ratio Ring and Pinion...I think!

      So what that evolves first is, finding out where the "break" is on Ring Gear size that requires a different "Carrier" to fit the ring gear, if it fits, which I think it does being just one range away, then just R&R-ing the ring gear to the other Carrier and installing it in the Avanti Housing. Then you will need the Rear Cover from the TT Axle to put on the former Open one.

      Sounds fairly easy, but I have to wonder how good the Pinion Height/Depth setting will be.
      Since you kept the Pinion and it's shims in it's original Housing, the only thing that could move would be the Ring Gear on it's new Carrier?

      You did not mention rebuilding anything so I am assuming that both are in very good condition.
      Last edited by StudeRich; 07-26-2013, 06:36 PM.
      StudeRich
      Second Generation Stude Driver,
      Proud '54 Starliner Owner

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      • #4
        Rich mention "finding the break." To clarify, all Dana 44 gearsets from 2.56 to 3.73 use the same carrier and 3.90 - 6.33 use the same carrier. Your 3.31 to 3.54 is in the same family.

        The new flanged 19-spline count axles will be fine unless one is regularly doing drag strip launches with more than 300 horsepower. As Bob said, then the higher spline count axles and carrier would be a good investment.

        As far as changing from a 3.31 to a 3.54 "waking things up nicely"; it's only a 7% increase in torque multiplication and RPM increase. Noticeable, but worth the money?

        My first choice is always to look around/ask around for an existing TT rear. They're out there and you've got everything in one package rather than buying it one piece at a time.

        jack vines
        Last edited by PackardV8; 07-27-2013, 08:07 AM.
        PackardV8

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        • #5
          Its not at all that difficult. I went the other way: 3:73 to 3:31. Installed Mosier Flanged axels from Fairborn, dropped in a Auburn Possie, Shimmed it all up the right way, i.e. both sides, and on down the road we went![IMG][/IMG][IMG][/IMG] Just a couple of hours on the lift.

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