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Speedo is WAAAAAYYYY off.

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by ajalecci, May 27, 2003.

  1. ajalecci

    ajalecci Newbie

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    I just re-geared to 4.56's and am running 33's. Right now, my speedo is about 20-25 mph off. I know I need to change the speedo gear but I don't know what size to change it to or where to get one. I think I have a th-350 but I am not sure. How can I figgure that out as well? Thanks for your help.
     
  2. Silver84k5

    Silver84k5 1/2 ton status

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    th350 has a square pan with one corner cut off, a th400 as a funky pan, 700r4 has a square pan....

    Just go find your self one of those Police Speed survey/ticket/take your picture thing.... and find out how far its off, then just remember it ;P

    Speedometers are overrated ;P
     
  3. jekbrown

    jekbrown I am CK5 Premium Member GMOTM Winner Author

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    my speedo doesnt work at all... honestly tho, I want it back. lol. I generally dont worry about speeding tickets... but it WOULD be nice to know if I was breaking the law at any given point. lol!

    j
     
  4. rampage

    rampage 1/2 ton status

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    A 700r4 has overdrive and a th350 doesn't - look on your shift column.
    The best way to determine your speed is to follow a friend on the highway while he is doing 60. Check what your speedo says. If it says 55 then it's 10% slow. Then just always add 10% to what your speedo says.
     
  5. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    [ QUOTE ]
    I just re-geared to 4.56's and am running 33's. Right now, my speedo is about 20-25 mph off. I know I need to change the speedo gear but I don't know what size to change it to or where to get one. I think I have a th-350 but I am not sure. How can I figgure that out as well? Thanks for your help.


    [/ QUOTE ]

    Well since y'all got an '88, I would venture to guess you have a 700. The speedo gear is more than likely located in the tailshaft housing of the transfer case.
     
  6. BlazerGuy

    BlazerGuy 3/4 ton status

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    Check out the local tranny shops, they probably have a bunch a gears laying around they'll let ya have for free. As for trying to figure out how much it is off, beg, borrow or steal a GPS for the most accurate reading. /forums/images/graemlins/smile.gif
     
  7. Blue85

    Blue85 Troll Premium Member

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    It doesn't matter what tranny you have because the speedo gear is located in the Transfer case tailshaft. Otherwise your speedo would be off by about 2:1 (depending on T-case) when you are in low range.

    For your calculations, account for any change in tire size from stock to present, as well as the gear ratio change. Gear ratios are exact, but tire diameters are often different from the rated size.

    This has been covered in detail before. Here's where I posted some info:speedo gear thread This change is very easy to do and the gears are inexspensive to buy. It gets a little harder if you have to change the drive gear also, but it is still doable.
     
  8. Silver84k5

    Silver84k5 1/2 ton status

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    [ QUOTE ]
    It doesn't matter what tranny you have because the speedo gear is located in the Transfer case tailshaft.

    [/ QUOTE ]

    good point heh didnt even think of that.
     
  9. Silver84k5

    Silver84k5 1/2 ton status

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    unless somone swapped stuff out, if you got in my truck and tried to put it in OD.. youd get pretty frustrated when OD never kicks in....... /forums/images/graemlins/thumb.gif
     

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