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    speedo adjustment

    Branching off from my previous 2 posts:
    http://www.mocgb.net/forums/showthread.php?t=14025

    Hi guys as im going to be getting new tyres fit on the back of my car changing from a 235/45/17 to 255/50/17 (rear wheels only) the speedo is going to be out by about 4 to 5mph over 70 so when doing 70 ill actually be doing 74-75... does anyone know how i'd adjust it in an 88? bear in mind the previous owner put in a knight-rider style console so its got a digital display... im hoping i wont have to fiddle with that to adjust it

    #2
    Never heard of a digital dash for a Fox mustang, so you're on your own there.

    However, you can change the speedo gear in the gearbox. This is usually done when changing the diff gear ratio, but it would do the same thing for your larger tyres. No idea about figuring out which one you'd need though.

    All you get is a tiny plastic gear. On my manual T5 box, it took longer to jack the car up than it did to change the gear.
    Wanted: rust free doors and front wings for 87-93 GT

    1988 Yellow Mustang GT

    13.97 @ 101.37
    MOCGB member 0425

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      #3
      Originally posted by Pod View Post
      Never heard of a digital dash for a Fox mustang, so you're on your own there.

      However, you can change the speedo gear in the gearbox. This is usually done when changing the diff gear ratio, but it would do the same thing for your larger tyres. No idea about figuring out which one you'd need though.

      All you get is a tiny plastic gear. On my manual T5 box, it took longer to jack the car up than it did to change the gear.
      well im on the steeda website so ill send them an e-mail and see if they can shed some light on which gear i might need... if no joy ill buy a whole set and begin with a bit of trial and error using my sisters sat nav unit :D
      How hard would you say it is to replace? i have an auto will it be any different on an auto box and where abouts would you locate it (lets say im going under from the drivers side?)

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        #4
        Originally posted by 1988 convetible View Post
        well im on the steeda website so ill send them an e-mail and see if they can shed some light on which gear i might need... if no joy ill buy a whole set and begin with a bit of trial and error using my sisters sat nav unit :D
        There's lots of websites with tables of which size gear (in teeth) to use for each diff ratio. I'd check what you have now and go one step up (or down), seeing as it's not a huge difference.

        How hard would you say it is to replace? i have an auto will it be any different on an auto box and where abouts would you locate it (lets say im going under from the drivers side?)
        I've never seen an auto box, so I couldn't tell you. On the manual, it's a cable which plugs into the drivers side of the box. Unbolt it, pull it out and the plastic gear is on the end. Swap them over and put it back in.
        Wanted: rust free doors and front wings for 87-93 GT

        1988 Yellow Mustang GT

        13.97 @ 101.37
        MOCGB member 0425

        Comment


          #5
          Originally posted by Pod View Post
          There's lots of websites with tables of which size gear (in teeth) to use for each diff ratio. I'd check what you have now and go one step up (or down), seeing as it's not a huge difference.



          I've never seen an auto box, so I couldn't tell you. On the manual, it's a cable which plugs into the drivers side of the box. Unbolt it, pull it out and the plastic gear is on the end. Swap them over and put it back in.
          i think i heard somewhere that its wuite similar to the manual so ill take a look... as for the gear ration im not sure what i have... i havent been able to get that technical just yet... im assuming its standard as the car seems to be morealess unmolested... then again im not sure what the standard ratio is... if u havent guessed already i h8 ratio's big time! its probably quite simple but it does my head in

          Comment


            #6
            Originally posted by 1988 convetible View Post
            i im assuming its standard as the car seems to be morealess unmolested...
            I assumed that about my car and just went by what the door tag said. I was wrong.

            You're probably looking at either 2.73 or 3.27 for stock auto gears. Could be 2.73, 3.08, 3.27, 3.55, 3.73 or 4.10.

            Easiest way to check is jack the car up. Spin a wheel one full turn and count how many times the drive shaft spins round. Or spin the driveshaft once and count how many times the wheels turn.
            If it spins two and three quarter turns, that's 2.73 and so on.

            Stock tyres were 225/60/15 for your 'turbine' style wheels. That makes for a overall height of 25.63 inches. For 17" inch tyres, 245/45/17 are the same height (25.68 inches). Your 255/55/17's are quite a bit bigger.
            See: http://www.tyresave.co.uk/tyresize.html
            It's much easier to stick with the correct height tyres in the first place. ;)
            Wanted: rust free doors and front wings for 87-93 GT

            1988 Yellow Mustang GT

            13.97 @ 101.37
            MOCGB member 0425

            Comment


              #7
              Originally posted by Pod View Post
              I assumed that about my car and just went by what the door tag said. I was wrong.

              You're probably looking at either 2.73 or 3.27 for stock auto gears. Could be 2.73, 3.08, 3.27, 3.55, 3.73 or 4.10.

              Easiest way to check is jack the car up. Spin a wheel one full turn and count how many times the drive shaft spins round. Or spin the driveshaft once and count how many times the wheels turn.
              If it spins two and three quarter turns, that's 2.73 and so on.

              Stock tyres were 225/60/15 for your 'turbine' style wheels. That makes for a overall height of 25.63 inches. For 17" inch tyres, 245/45/17 are the same height (25.68 inches). Your 255/55/17's are quite a bit bigger.
              See: http://www.tyresave.co.uk/tyresize.html
              It's much easier to stick with the correct height tyres in the first place. ;)
              if i stuck with the right height it wouldnt be much of a challenge would it :D plus i want domething nice and big on the rear... someone suggested i hire michelle Mcmanus :s
              will check the ratio's as soon as i get home tonight... are the speedo gears easy to get a hold of here or might i have to order US???

              Comment


                #8
                Speedo gears.........

                Have a look at this thread that I started on the Mustang Registry website in the states. It has some links to useful tables that might help you fathom out which way to go...
                http://www.mustanggt.org/forums/showthread.php?t=47095

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                  #9
                  Originally posted by Raven68 View Post
                  Have a look at this thread that I started on the Mustang Registry website in the states. It has some links to useful tables that might help you fathom out which way to go...
                  http://www.mustanggt.org/forums/showthread.php?t=47095
                  Hi thanks yeah that does help kinda narrows it down a bit... just need to figure out which to get now... id assume because the rear wheel would be turning slower with a large tyre that ill need so get a gear one size smaller than what i currently have to keep up to speed... so just need to do what i was meant to do last night and check the current ratio just too tired an been rewiring a new fog light for the rear of the car...

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                    #10
                    This doesn't apply to an '88 but maybe would be relevant to a digital dash? But I've really no idea.:D It suggests earlier Mustangs use a plastic wheel to drive the speedo.
                    http://www.brothersperformance.com/c...oducts_id/1327

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                      #11
                      If the digital dash is general purpose then it will have switches to set up the calibraton.
                      If it's Mustang specific then it may not have them.
                      The gear on an auto is on the end of the speedo cable where it fits in the box auto typr speedo gear is different to manual.

                      http://www.latemodelrestoration.com/...gory=MSPEEDCOR

                      There are speedo gear calculators on some web sites, input wheel size, rear gear size and it tells you what colour gear to buy.

                      Close to the bottom of the page:
                      http://www.ford-aode.com/

                      .
                      Last edited by mad4v8; 05-06-2007, 03:08 PM.
                      Stuart
                      2014 GT/CS

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                        #12
                        k i just did the drive shaft turning thing to work out what gear ratio i have... i turned the wheel one full turn and counted every quarter and it came to just over 1 and a quarter turns??? maybe i did something wrong??? anyone help???

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