direct swap for 2-series 71 Skylark 8.5" 10 bolt?

Discussion in 'Got gears?' started by tball, Jun 8, 2018.

  1. tball

    tball Member

    That's how eBay gets you, the " check if this fits your particular vehicle " button...
    Not so reliable...
    Thanks for the heads up
     
  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Jim, I linked him to the correct Timken bearings in post 35. From, Sumitt, not sure if that is the best price.
     
  3. tball

    tball Member

    Thanks everybody, the new gears, posi unit and all bearings seals races fluid additive etc. are installed.
    Thanks for the heads up steering me away from the "gov-bomb" posi...A little homework goes a long way-
    Big thanks to Quick Performance for the phone advice and great pricing.
    The car is like new, what a difference taking off, very pleased.
    The toughest part is the break-in period- 500 miles of taking it easy, no hard acceleration?? That's like putting a cold beer in front of a guy in the desert, "Don't touch that!"
    Now I just need to figure out the new math for my speedometer...
    Stock tires were 26", now 28". Stock gears were 2.73, now 3.73.
    Speedo seems to read about 10 mph faster than actual, give or take- 8.5posi-brgs-races.jpg 8.5posi-brgs-races.jpg s-l400.jpg
     
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Speedometer gearing is easy. Just need one more piece of information. tooth count of the distributor DRIVE gear. The DRIVE gear is on the output shaft. If you remove the DRIVEN gear sleeve, you can see it. It's a helical gear. If you get the back of the car high off the ground, you won't lose much fluid. Rotate the driveshaft with the trans in neutral and count the teeth. For the THM 400, it should be 16, 17, or 18 teeth. My GS had a 16 tooth gear. I also had 3.73's with 28" tires. It took a 43 tooth DRIVEN gear. Just plug in the numbers.

    http://www.tciauto.com/tc/speedometer-gear-calculator

    You may need to change the DRIVE gear if it isn't the 16 tooth. Either that or get a reducer.

    https://www.bobsspeedometer.com/1/120/ratio_adapter.asp
     

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