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Speedo Gear

Discussion in 'The Garage' started by k20, Dec 2, 2003.

  1. k20

    k20 3/4 ton status

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    I changed tires from about a 31.5" tire to a true 35. Where do you get the speedo gear for a th400? I think it goes in the side of the tranny is this correct? Also which gear do i get, and how do u determine which you need?
     
  2. 84_Chevy_K10

    84_Chevy_K10 Banned

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    [ QUOTE ]
    I changed tires from about a 31.5" tire to a true 35. Where do you get the speedo gear for a th400? I think it goes in the side of the tranny is this correct? Also which gear do i get, and how do u determine which you need?

    [/ QUOTE ]

    Speedo gear for a 4wd truck is in the transfer case, not the transmission. If it was in the transmission it'd read WAY wrong when in low range. Not to mention it'd be in the middle of the TC input. /forums/images/graemlins/smile.gif
     
  3. k20

    k20 3/4 ton status

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    o ok, where do u get the gear and how do u determine how many teeth the gear needs etc?
     
  4. 99firehawk

    99firehawk 1/2 ton status

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    You need to have some one drive next to you and figure out how many mph you are off. Take out your exisiting gear pass side of t cas, and see what the # on it is, every 2 mph is one tooth, if it reads slow you need gear with more teeth, if it reads fast then you need one with less teeth. You can get them at any transmission shop they are 8-12 $ a piece.
     
  5. skratch

    skratch 1/2 ton status

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    I'm still looking for it but i had the formula around here somewhere.
    It will allow you to figure both the driven and the drive gears that you need. I have no idea where to get the gears for your case though. If the driven gear is the same as a 208 0r 700 then you can buy those from 700R4.com or the dealer once you know which one you need.

    I'll keep digging around to find that formula, but my desk is a disaster after putting up the tree. /forums/images/graemlins/crazy.gif
     
  6. K5Jimmy

    K5Jimmy 1/2 ton status

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    I did this just today as a matter of fact....89 700R...Speedo shop at first told me it was a "calibration" adjustment programmed under the dash....Then they told me that since it's straight cable drive, I would need an adaptor...Early 89 is cable drive, late 89 is "Tone Ring" calibrated (?)

    So I took it to the guy they reccommended, and he Built me a Speedometer gear adaptor....I run 4:10 and 33" w/700R/241 ...we drove a Measured mile he had marked off, and figured I was like 12% off...1 mile = 1.15 on my speedo...so he built me a little gearbox that bolts on where the cable goes, and the cable goes on to it...Speedo now reads Perfect...I asked about just changing the gear in the tailshaft, and he said that depending on how much of a change you have to make, you make have to change the worm gear also, and that this was the most accurate way to go....Gearbox and HD speedo cable with housing was all of $65....my cable had been laying against the exhaust and was burnt sorta bad...I personally got more double talk from Tranny shops than anything else...I was referred to Autocraft by the guy who built my Tranny...Autocraft put me in touch with a guy with 42 yrs in the business...don't know if this does you any good, but I'm happy with what I got...
     
  7. 69K5

    69K5 1/2 ton status

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    i put the formulas or links to em up for ringmaster4x4. search for his name or mine and they should be there.

    69k5
     
  8. k20

    k20 3/4 ton status

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    thanks guys, much appreciated.
     

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