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Speedo drive pinion.
  • Geoff C., N.Z.Geoff C., N.Z.
    Posts: 2,273Platinum Member
    Can anyone please help me locate a drive pinion for the speedo drive that fits in the back of the overdrive on my Jet?
    It is a short shaft that fits in the end of the cable, and has a fiber gear on the end of it with 16 teeth. Thanks,
    Geoff
    If you're stuck in a hole, stop digging.
  • Uncle JoshUncle Josh
    Posts: 1,863Platinum Member
    Geoff, there is a chart in the stuff that Alex has posted online with part numbers etc. Went thru that with the guys in Sweeden a while ago. If you can't find it email me. I think I have a copy someplace.
  • Park_WPark_W
    Posts: 2,055Platinum Member
    Geoff, that pinion should be Stewart-Warner #448379 for the 4.1 or 4.27 axle gears, and 448409 for the 3.54 gears. Both are 16 tooth
  • Geoff C., N.Z.Geoff C., N.Z.
    Posts: 2,273Platinum Member
    Thanks for the info Park. Does anyone know where I can get one?
    If you're stuck in a hole, stop digging.
  • AndreasAndreas
    Posts: 23Hitchhiker
    Hi Geoff
    I know from my own experience that they are hard to find, I was able to get a 16 teeth from E-Bay a year ago, that one had the gear in steel and not fiber as my original one.
    If I'm right the steel one belonged to the pre 48 era.
    Works fine with 16 steel teeths but do NOT gives a correct speedo reading, for my C6-1950 3speed w OD (4:10 rear) I should probably need a 18 teeth to get the correct reading.
    / Andreas
  • Park_WPark_W
    Posts: 2,055Platinum Member
    Andreas, the book shows 16 teeth is correct for a '50 with OD and 4.10 rear end. Is your odometer way off, or pretty close?
  • lostmindlostmind
    Posts: 545Gold Member
    Tire size effects reading , radials are not as " Tall" .
  • aminardaminard
    Posts: 87Senior Contributor
    To slow down a speedo reading do you change the gear to more teeth or less teeth than the one you have installed in teh trans?

    Allan
  • Geoff C., N.Z.Geoff C., N.Z.
    Posts: 2,273Platinum Member
    To calculate the gear ratio of a worm you count the number of spirals on the worm, and divide into the number of teeth on the pinion. To change the ratio you have to change both the worm and the pinion. Just F.Y.I., the Jet uses different worm and pinions for the standard and o/d boxes. Not sure on Step-downs. I thought I would use the pinion from a standard transmission, but the teeth slope the opposite way.
    If you're stuck in a hole, stop digging.
  • AndreasAndreas
    Posts: 23Hitchhiker
    Park, At 70mph it shows approx 10 too much, maybe it’s what you could expect out of stuff that is +60years old…Running 225/75X15 radial tires so that might be the explanation?
    Aminard, If I’m right to slow down the meter you should add a bigger pinion.
  • Geoff C., N.Z.Geoff C., N.Z.
    Posts: 2,273Platinum Member
    You cannot just "add a bigger pinion" because it will not mesh correctly with the spiral worm on the shaft.
    If you're stuck in a hole, stop digging.
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