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1.35:1 Gear ratio?!?!?!?!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by oh-zj-io, Nov 12, 2006.

  1. oh-zj-io

    oh-zj-io Registered Member

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    Hey!

    Got the motor and tranny swap done in the 88 K5. I was going to put the 35s on it today so I thought I'd see what I needed to do to the speedo gears to get them corrected.

    Rather than pull a dif cover I jacked it up to do the tire spin and driveshaft count. I will readily admit that I am not a mechanic and that most of what I do to our vehicles is a learning experience. But I was totally surprised at my results.

    Does this make sense??? If it does make sense, what would be the reason for this gearing?

    Per one rotation of the rear tire the rear driveshaft rotated approx 1.35 turns. Is this right?

    So I stopped and didn't pull the speedo cable to check the drive gear...I'll wait to make sure I am not missing something here.

    Thanks,
    Al
     
  2. huntingaddict

    huntingaddict Registered Member

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    With a rear that has a posi or spool, etc. it turns the ratio as expected. Somehow or another with an open diff it seems to turn half of the larger number in the ratio. Hope this makes sense. It sounds wierd, but has happened to me numerous times.

    Tom
     
  3. oh-zj-io

    oh-zj-io Registered Member

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    Hey!

    So you are saying that from your experience I may be at 2.73 or something like that due to having open diffs?

    Al
     
  4. MattK

    MattK 1/2 ton status

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    thats correct. i'd pull the cover and count teeth. a little more of a pain in the ass, but im sure the oil could use changing.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    If it's stock, it's going to be 2.73 or 3.08's based on your numbers, really doesn't matter when the numbers are that low, they both suck. :)

    You are really going to put the hurt on that tranny with those tires, an auto, and 35's though, FYI.
     
  6. oh-zj-io

    oh-zj-io Registered Member

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    Hey!

    It's got 33's on it now and I think I'll leave them for a while. At least until I figure out what to do about those gears. Guess I assumed that they were better than 2.73s. :( So it wasn't all just motor and tranny problems...that gearing had a lot to do with the way it ran!

    Thanks guys! Appreciate it.

    Al
     
  7. oh-zj-io

    oh-zj-io Registered Member

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    Hey!

    Yep, that's my plan. I just didn't want to do it out in the cold today. Swapping tires is one thing, but....

    The diff fluid is all that's left to be changed. That and the brake fluid, but, I don't think I'll be attempting that little project..:D ;)

    Al
     
  8. Confedneck79K30

    Confedneck79K30 3/4 ton status

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    block the front wheels, lift up the rear, pull the diff cover, look for the numbers stamped into the ring gear, and report them here... i bet you have 2.73s if its doggy with 33s....
     

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