'73 speedometer adjustment

[greenWX]

I was recently have problems with my speedometer cable, so I installed a new one. However, the speedometer reads 30mph with the engine off and when driving down the road it ticks up to 60mph when I know I'm barely doing 20mph. How would I go about fixing this?

[XH29N0G]

The speedometer hair spring should bring the needle back to its resting point.  My guess is that your speedometer needle is binding somehow or the spring is damaged. 

You might be able to degrease your needle (if it is grease and dust clogging it) or free it up if it is binding, but I suggest you either send it out to get it fixed at a speedometer shop (redline gauges is one that refurbishes them - I believe) or you buy a replacement.  There are likely replacements at places like classic industries that you could just swap in.  Both options will be expensive, but from my own experience it takes a lot of skill to fix and recalibrate one of these speedometers.   

[Nacho-RT74]

probably plastic bushing what keeps the return spring in place went to the speedo's heaven

[greenWX]

I unplugged the cable and it reads 30 still is that the spring you where talking about?

[XH29N0G]

If you take the speedo out of the dash, it will look something like this (at least for a 1970).  The yellow part is where the hair spring is situated.  It is a very fine, spiral spring that can be deformed.  The speedo operates by having the stuff spin in the part outlined in green.  There is a magnet at the end of this, that spins inside the cup, which exerts a force on it that is transferred through the spindle (outlined in yellow) to the needle at the front of the gauge.  The hair spring is attached to the spindle and exerts a counteracting force that keeps the needle at a certain point for a given spinning rate.  The speedo is a delicate balance of forces and an ingenious design.

The things that can get messed up are the plastic bushing that the spindle passes through, the hair spring, or something else.  It seems like your speedo is binding and the plastic bushing noted by Nacho-RT74 is the likely culprit.  I tried to fix this one in the picture myself.  I failed.  I also tried to fix another one myself and failed again.  You may be more handy with these than I and may be able to fix it.  I am happy to explain more about what I learned.  There is also plenty on the internet. 

[71charger_fan]

To pull the speedometer, you have to pull the cluster, which means dropping the column. I just switched speedos in my '71 and it's not a quick job. Just so you know.

[Nacho-RT74]

I have fixed 2 with success. Will post pics later

[Nacho-RT74]

Actually the theead about the bushing problem on the 1st speedo I damaged ( and fixed )

http://wichargerguy.proboards.com/thread/19119/patiente-pays-brock-thing-help?page=2

But later will get you a better view of rhe fixing on the 2nd speedo I fixed on the bushing. And explanation

[ODZKing]

Frankly I have never seen a 71-74 speedo that didn't have a problem of some sort eventually.  They all bind, they all stick ... must have been a terrible design.
But having said that they are everywhere ... especially the 120's ... just find another one unless you are set on keeping the exact mileage.
Here is a 150
http://www.ebay.com/itm/MOPAR-71-72-73-74-B-BODY-CHARGER-ROADRUNNER-RALLYE-DASH-CLUSTER-150-SPEEDOMETER-/122215188261?hash=item1c7497c725:g:moAAAOSwZ1BXgFTe&vxp=mtr
Another
http://www.ebay.com/itm/Mopar-b-body-speedometer-1971-74-150mph-Charger-Roadrunner-Gtx-/112135530696?hash=item1a1bcc68c8:g:goIAAOSw4shX2HI2&vxp=mtr