1970 Roadrunner Speedometer Jumping Around

1968 -1970 Mopars

  1. RoadRunner1970

    RoadRunner1970 Well-Known Member

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    If my speedometer needle is jumping around when I drive is that the cable or the speedometer? It is a new replacement cable on it right now.
     
  2. kiwigtx

    kiwigtx International Mod Staff Member FBBO Gold Member

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    Cable may not be seated correctly...or a dry inner sleeve.

    Make sure pinion drive gear was seated correctly also.....and dialed in to the correct range as per the tooth count.
     
  3. dadsbee

    dadsbee FBBO Gold Member FBBO Gold Member

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    Pop your cable off the transmission and run it with a drill IN REVERSE !!!! See if it runs smooth.. go VERY LIGHT on the speed. Will remove the drive rear from the equation.
     
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    • beanhead

      beanhead Well-Known Member

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      Mine goes wild all over too; I've verified it's the speedometer itself but oh well. It's gonna be a long time before I tear back into the cluster and send it off to be repaired..driving by tach is good for now!
       
    • Darter6

      Darter6 FBBO Gold Member FBBO Gold Member

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      At the rear of the speedo where the cable connects to there is a brass bushing. Lube that bushing with vaseline on the tip of your finger.Don't be shy.Pack it like you would a bearing.With the new cable pull it out to see if it has been lubed from the factory. I just installed a new cable on my 65 and it had no lube at all.Years ago a gauge shop turned me on to using vaseline as cable lube.It coagulates and never dries out.I've done this on many old cars and motorcycles with great success.
       
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      • PurpleBeeper

        PurpleBeeper Well-Known Member

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        Most likely the new speedometer cable isn't greased. I would want to slip the cable out & spray it down with a graphite spray (I'm about to do this on mine). I do have to say that Darter6's idea about greasing the back of the speedometer with Vaseline sounds like a really, really good idea too.....cheap and effective. That inner metal cable will pull completely out pretty easy in one direction....anybody remember which end you'd disconnect to pull the metal cable out without removing the outer casing from the car? Speedo side or trans side?
         
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        • pearljam724

          pearljam724 Well-Known Member

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          There is a plastic bushing that the speedometer needle stem goes through on the actual rectangular speedometer. They crack due to age. Once they crack they are unrepairable. Unless you find another plastic bushing from another speedo.
          An easy way to check for this problem is your needle doesn’t always rest at 0 mph. Or lightly move the needle by hand to higher speeds. If the needle doesn’t crack back to zero on its own with sprung force, once you release the needle. The bushing is cracked.
          When the bushing is cracked. It causes the stem to rise in and out of its fixed position. This causes the needle to work sometimes when the bushing falls back to where it’s supposed to be and doesn’t work sometimes when the bushing rises out of it supposed to be fixed position.
          When it goes in and out of its fixed position. This is why the needle bounces around erratically. But, erratic needle movement can also be caused by an old cable that needs lubed or replaced.
          If you look at the bushing the needle stem passes through, you can see if it’s cracked or not. Also lightly grab the needle where the stem is, if needle and stem moves in and out as you lightly pull on it. Bushing is cracked. It’s supposed to be in a stuck position with no movement in and out.
           
          Last edited: Sep 4, 2019
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          • RoadRunner1970

            RoadRunner1970 Well-Known Member

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            If I have to replace the speedo cable how hard is it to get to it, and if I have to replace the the speedometer can I keep the original odometer?
             
          • beanhead

            beanhead Well-Known Member

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            The cables are pretty easy. Unclip from the back of the speedometer, then pull it through the firewall grommet. There is one bendable metal tab that holds it under the car; open it up with pliers or whatever and then it un-screws from the transmission. I don't know about the odometer..
             
          • pearljam724

            pearljam724 Well-Known Member

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            You can keep odometer. There’s a trick to that. Take cable off tranny only and pull the cable up through the dash when you pull Speedo. You have to remove dash pad, which is very easy. But a pain to reach all nuts that hold it on. Look at the bolts on a used dash pad for sale or google one. This will help you find them on yours. Most are easy to reach. A couple are not.
            Removing ash tray is key. Use your phone on video mode to find the nuts. It’s best to remove driver seat, it only takes 10 minutes. This makes it a thousand times easier reaching the dash pad nuts. You can lay on your back to reach them. Otherwise a couple of them are tough to reach. But, a very easy job. Don’t forget to unhook your battery, first. Install speedo, before you reinstall dash pad. It’s tough to find a nice speedo at a reasonable price. I got lucky. I found a mint one for $150. That’s not normal. Very nice ones usually sell for a few hundred and poorer condition ones at $150.
            The nice thing about all of them though.
            You can easily swap all junk or good parts. Not a part on them that you can’t.
             
            Last edited: Sep 6, 2019
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            • pearljam724

              pearljam724 Well-Known Member

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              Just returning the favor, for buying my wheels.
               
            • beanhead

              beanhead Well-Known Member

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              This is excellent advice..Easy to get stuff arc'n & spark'n when you're fumbling around under there with metal tools!
               
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              • pearljam724

                pearljam724 Well-Known Member

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                Yep and find out, you burned all of the bulbs in the speedo after you fought to put it in, lol ! Test the bulbs too, before you install it. Easy, just remove the bulbs and hook leads from the prongs to a 12 volt battery. Doing so, will save some fighting later.
                 
                Last edited: Sep 6, 2019
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