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speedometer

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  • #454538
    raceking1324raceking1324
    Participant

      ok now on my 91 explorer my speedometer is off by like 5,10 mph how can i fix it or what can i do to fix it

    Viewing 9 replies - 1 through 9 (of 9 total)
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    • #454539
      MattMatt
      Participant

        Odd question, but are yer tires set at the correct pressure? If they are both low and severly worn, that alone will cause your speedo to read a bit faster than yer actually going. Just a thought.

        #454540
        jbonejbone
        Participant

          And how do u know this? what are u comparing it to?..Like beefy
          said tires will do this, if size is wrong or pressure is low,or maybe your instrument panel is on the fritz…Post back on your findings….thanx

          #454541
          dreamer2355dreamer2355
          Participant

            Does your speedo needle bounch around at all? You could try using some graphite lube at the back of the speedo where your cable plugs in.

            #454542
            MattMatt
            Participant

              The reason I have noticed the difference between old low pressure tires is because I deliver pizzas, and in the area I deliver in, the cops set up alot of those radar guns attached to a giant LED sign telling you how fast you’re going. I have been past the same one and my speedo shows 4 or 5 mph higher than the sign, and then literally the next day when I replaced the front tires on my geo prizm, it was a couple mph closer. I also had an astro van that had a speedo that was WAY off, and I pulled the whole cable, and pulled the spring out of the sheath and greased the whole thing up very liberally. That fixed my problem, because there was corrosion in the cable. Another thought–make sure you have the correct size tires on yer truck.

              #454543
              EricTheCarGuy 1EricTheCarGuy
              Keymaster

                Beefy is on the right track with tires but the real issue would be if you have different sized tires than stock. If you changed the wheels and tires to a different size that could cause that issue. Other than that it could be a problem in the cluster or the gear that goes into the transmission, to make that determination some testing would be in order. I would start by pulling the gear out of the trans to have a look at the teeth on the gears to look for any wear.

                #454546
                BigCBigC
                Participant

                  Hi raceking1324. I checked tirerack.com for the tire size of your ’91 Ford Explorer. There are two equipment packages listed.

                  Package #1: 225/70R15
                  Package #2: 235/75R15

                  DId the concern with the speedometer occur before or after the transmission rebuild? If it occured before the rebuild, then double check your tires to make sure they conform to the specs listed above. I deviation in either tire size would result in a different revolutions per mile for that tire. That could be enough to affect the speed sensor in the transmission and produce an inaccurate speed.

                  #454547
                  RichRich
                  Participant

                    The first gen explorers had two different size tires that you could mount on the rims(BigC is correct). P225/70R15(stock) and P235/75R15(optional) depending on which size you have on your car, you needed to change the gear on the speedo. Do exactly what Eric said and count the number of teeth that the gear has. I cant remember though if you had to lose or gain a tooth on the gear W-| The speedometer cable goes into the transmission tail housing, it should be a black cable. Hope this helps!

                    EDIT: To find out how many teeth you need use the following formula
                    New Teeth = (Current Teeth x Speedo Reading)/Actual Speed

                    There are different colors for each gear here are the gears and the Ford part numbers

                    16-teeth-blue (D0AZ-A)

                    17-teeth-green (C7SZ-A)

                    18-teeth-gray (C7SZ-B)

                    19-teeth-tan (C7VY-A)

                    20-teeth-orange (C8SZ-B)

                    21-teeth-purple (D0OZ-B)

                    #454544
                    raceking1324raceking1324
                    Participant

                      ok the rims are 15 and i think they are stock and do u think if i buy a new cluster it mite fix it??and i just had a shop rebuild my trans so i know that’s all good

                      #454545
                      EricTheCarGuy 1EricTheCarGuy
                      Keymaster

                        Now THAT is an important clue, if they broke the speed sensor during the rebuild they may have put a new one in that is not correct or perhaps the old one is not installed correctly. Anytime you have an issue after doing work it’s always a good idea to go back and check the work.

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