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Baffling question !! really.. (kinda long) goes with my other post.

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by rocko, Dec 12, 2001.

  1. rocko

    rocko 1/2 ton status

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    Okay.. as some of you know.. I swapped out the rear in my 89. Went from 2.73's to 3.73's..
    Of course the truck is a rocket now... I'm truely impressed by the difference.. But here's the deal..
    Does the gear ratio affect my Tripmeter on my speedo?
    Now I'm calculation my speedo is off by about 20 mph...
    But I'm getting the best mileage I've ever had with this truck...
    Getting over 400 miles per tank.. I'm at 1/4 tank now.. and it reads 397 miles on the tripmeter..
    This is unbelievable or what? I used to only get maybe 340 miles per tank..
    Now the 3.73's sure do make the truck work less.. it's kinda effortless to drive..
    Help me on this.. tell me I'm not crazy.!!!
    Thanks in advance..

    I haven't failed, I've found 10,000 ways that don't work. www.rocko.rockcrawler.com
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Speedometer cable drives both, so yes, your odometer reading is screwed.

    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>www.dorianyeager.com/index2.html</a>
    Why insist on counting when the ring gear has the tooth counts stamped in?
     
  3. kpanza

    kpanza 1/2 ton status

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    Of course it will read higher! Have a friend pace you on the highway, drive one exact mile (by your friend's car if he has a correct speedometer!), and you will be able to estimate how far off you are...your odometer is gonna "show" more mileage than you are actually driving, that is why it "appears" that you are getting way more miles to the gallon! I would guess that your speedo/odometer is off by somewhere around 10-20%...

    Hope I didn't burst your balloon! [​IMG]
     
  4. rocko

    rocko 1/2 ton status

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    Cool.. thanks guys..
    Guess I better fill up.. lol... I was getting all excited about the mileage... oh well..


    I haven't failed, I've found 10,000 ways that don't work. www.rocko.rockcrawler.com
     
  5. surg82k5

    surg82k5 1/2 ton status

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    Charles one other sure way to tell how fast you are going is to get your hands on a good GPS system, I know that some of them will be able to tell you how fast you are moving and even at what altitude. Hope this helps a little,
    Sergio

    Check out my new website. <a target="_blank" href=http://www.surg82k5.rockcrawler.com>http://www.surg82k5.rockcrawler.com</a>
     
  6. 81Bogger

    81Bogger Registered Member

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    My favorite way to test the speedo is find those "traffic control" radar things that have a radar and a big display screen saying how fast your going.......... ever see one of those things read 70??.......... it's pretty cool..... [​IMG]

    <font color=red>81</font color=red><font color=blue>Bogger<font color=blue>
    "<font color=blue>Mud under tire, and Fords in the rear view...<font color=blue>" [​IMG]
     
  7. JIM88K5

    JIM88K5 1/2 ton status

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    Check your speedo against the mile markers on the freeway...
    -Jim

    88 5.7 5in lift 35"procomp at's
    700-208-456-3in exh w/flowlowder 10 bolts & some ORD stuff
     
  8. 6.2Blazer

    6.2Blazer 1/2 ton status

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    It looks like you are running 35" tires, correct? Even with your speedometer and odometer being off there is still a good chance that you picked up some mileage gain when going with the 3.73 gears since they should put the motor into a more efficient power range on the highway.

    Did you run the larger tires with the 2.73 gears? Did you correct the speedo after putting on the bigger tires? If you put larger tires on with the stock gears than the speedo/odo will actually show less miles/slower speed, meaning that before the gear change you might have been getting better mileage than you really thought.
     
  9. Executioner

    Executioner 1/2 ton status

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    Nah, try 93 on radar, speedo read more than 85 and some change !
     
  10. rocko

    rocko 1/2 ton status

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    This is on my 89 Blazer..
    I have 31 inch tires for now.. went from 2.73's to 3.73's..
    And The speedo was dead on prior to me swapping the new rearend in..
    I just need this gear thing for the t-case.. then I'm set.. til Iift the truck.. lol..

    I haven't failed, I've found 10,000 ways that don't work. www.rocko.rockcrawler.com
     

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