I have a 1968 Dart GT. The speedometer stops at 60 mph. The needle stops moving and just sits at 60. When I slow down it drops back down. I have replaced the speedometer unit in the instrument cluster. I checked to make sure there was not any interference inside the unit. The car was recently restored and I had a late 60's cruise control installed. The unit works properly and holds any speed at which I set it regardless of speedometer reading. I have an extra unit, so I exchanged them. None of this has worked. Does anyone have any ideas? Thanks

 

Pull out your flexible speedo drive cable and inspect it. It sounds like there is a break somewhere.

 

I pulled the drive cable and greased it prior to installing the new speedometer assembly. Sorry I left that out of the original post.

 

Consult the service manual for the correct speedo gear adjustment on the trans. The plastic gear may also be worn to a point it is slipping.




Maybe a free manual download here..................
http://www.mymopar.com/index.php?pid=109