Speedometer not at Zero

[Wcalmt]

I have a 4 door 66' dart 270, The speedometer has been getting worse by not going back to Zero, it now reads 75 at a stop, any ideas? :wack:

 

[halifaxhops]

Don't stop?

 

[1968FormulaS340]

I would start be pulling the cable and cleaning it inside and out then lightly greasing it.

If that doesn't do it, pull the speedo, and clean it. You can use compressed air in a can, I have also used spray electrical cleaner from RadioShack.

 

[Rocky_JS]

It would still zero out if the cable was bad.
The problem is in the speedo head. There is a disc and shoe that works similar to a centrifugal clutch. It is possibly binding in that area from dirt or corrosion between them. Pull the dash cluster and remove the speedometer and inspect and clean as necessary.
There is also a small clock spring that brings it back to set zero that may have broke. To fix that you'll need to remove the face which is held on by 3 small rivets remove 2 of them you can swivel it out of the way to inspect.

If the disc/shoe were really binding it most likely will also peg out fairly easy however if the spring were bad it wouldn't return the needle back.

You could just find a known good speedo head and replace it as well.

 

[nm9stheham]

^^^ Exactly, it is not in the cable. But lubing it is a good idea as preventative maintenance.

 

[Pawned]

on my Duster, I looked at the speedo and there is a fine spring before it gets to the needle. I found if I played with the position of the piece of metal that anchors it, I could get it to return to zero. Also I could get the speed more accurate.
I used super glue to hold it in the position I wanted, then when I needed to adjust it, I would get a dentist pick and us it to free the metal, it chips away somewhat easily, move it a couple millimeters and re-glue it.
It was trial and error. took many attempts to adjust it, now I am only a couple mph off and I now leave it alone

 

[Rocky_JS]

^^^ yes that is true. The spring is anchored on to the shaft and its tension is set with a rod that the other end of the spring goes through. The spring rod is secured in place by a small nut. It is possible the nut came loose enough to relieve the tension on the spring. I would think it a very rare occurrence that would happen though but certainly it is possible.

It is costly to send a speedo out to be repaired and think the most cost effective outcome would probably be to replace the speedo assembly. Or go into a repair with that in mind and try fixing it yourself depending on your abilities.

 

[Pawned]

I called a local shop and they wanted about $200. Thru trial and error, I fixed it and cost me the price of a tiny tube of superglue.

 

[hemitheus]

It would still zero out if the cable was bad.
The problem is in the speedo head. There is a disc and shoe that works similar to a centrifugal clutch. It is possibly binding in that area from dirt or corrosion between them. Pull the dash cluster and remove the speedometer and inspect and clean as necessary.
There is also a small clock spring that brings it back to set zero that may have broke. To fix that you'll need to remove the face which is held on by 3 small rivets remove 2 of them you can swivel it out of the way to inspect.

If the disc/shoe were really binding it most likely will also peg out fairly easy however if the spring were bad it wouldn't return the needle back.

You could just find a known good speedo head and replace it as well.

^^^ 5000% accurate.