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Pinion Gears - Which one will work?

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  • Rear Axle: Pinion Gears - Which one will work?

    Seeking a bit of advice from some of our "experienced" mechanical folks...

    As you may know, my '57 Transtar has a transplanted T-86 O/D transmission installed. The differential is a 4.09 ratio. I have noticed in my travels that the speedometer reads about 10% less than the true road speed. As the truck has 215/85R16 tires (approx. the same diameter as the 8.00 x 17.5 used on 1 ton Transtars and at least 1.5-2 inches greater in diameter than the standard 6.00 x 16 tires), I am assuming that this "larger in diameter" tire size is the largest contributor to the speedo error.

    In the Truck parts manual it shows the standard pinion as #682017 for my model(assuming I had a T-89/90 tranny) and #682014 or #682015 for a truck (with the same r/a ratio and larger diameter tires. Of course, these parts numbers also relate to the T-89/90 transmissions.

    The questions: Do these part numbers have any relevance to the T-86 transmission, or do I need to find a car parts manual to figure out what pinion may be in order? Would any of these pinions fit in a T-86? If not, the problem may be finding any specs in the car manual for "bigger" diameter tires as cars generally had smaller diameter tires from the factory than the trucks.

    Thoughts/comments? [8)]

    <h5>Mark
    '57 Transtar Deluxe
    Vancouver Island

    Are you planning to attend the NW Overdrive Tour in Parksville, BC
    May 23 & 24, 2009?
    </h5>
    Mark Hayden
    '66 Commander
    Zone Coordinator
    Pacific Can-Am Zone


  • #2
    Maybe this will help
    http://www.bgsoflex.com/speedo1.html

    Comment


    • #3
      Mark - which pinion did you end up using and did it work. I have an E7 truck with a T86 overdrive and it looks like I need a 682017 pinion

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      • #4
        I have 4.09 ratio axle and 15" tires

        Comment


        • #5
          RE: Pinion Gear

          Originally posted by ncalder View Post
          Mark - which pinion did you end up using and did it work. I have an E7 truck with a T86 overdrive and it looks like I need a 682017 pinion

          I had to check the post date of this thread to figure what this was about! I did dig through my old e-mails and found this:
          "it appears the closest is part #1544759 a pinion with 17 teeth"
          So, I am certain that is what I ended up installing and it reads within about 2-3% of true as a result. Hope this helps.

          Mark Hayden
          '66 Commander
          Zone Coordinator
          Pacific Can-Am Zone

          Comment


          • #6
            Thanks Mark, I'm trying to use that formula to determine my pinion now I've found out my tires are 27.68" I have a couple of unknowns (1) the number of revs per mile of the speedo (maybe 1000) and the teeth on the drive gear - it looks to be 6 or 7 is there a standard for a T86 1A? If the speedo revolutions per mile is 1000 the pinion is either 18 (for 6 tooth gear) or 21 (for a 7 tooth gear). Its hard to see the extent of the teeth through the speedo drive hole.

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