Find gear ratio on pete 389

Discussion in 'Peterbilt Forum' started by Wespipes, Aug 30, 2020.

  1. Wespipes

    Wespipes Road Train Member

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    Mystery is solved! Its 3.42. Which is good news to me. Was told 3.25 when I bought the truck lol
     
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  3. JonJon78

    JonJon78 Road Train Member

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    Why is 3.42 vs 3.25 good news? Just curious...
     
  4. Wespipes

    Wespipes Road Train Member

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  5. pushbroom

    pushbroom Road Train Member

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    DSP40 diffs 3.42 ratio as you found out already.

    If the ecm was set for a different diff ratio it just makes the speedo inaccurate.
     
  6. Geronimo17

    Geronimo17 Light Load Member

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    Good luck with the truck. Any photos?
     
  7. dirtyrabbit

    dirtyrabbit Medium Load Member

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    If you walk into the dealership, they can print off a build sheet for the truck. Every time I've gotten into a truck, I've made that request and always had them handed right over.
     
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