Joe, most folks can unscrew the cable at back of the speedometer. First thing is get a good look at it and to that end try this; find a board about 4' long and 12" wide or so. Then lay one end in the floor of the truck, the other end is supported with a chair, 5 gal bucket or what ever is handy. You can now lay comfortably on you back and look under the dash with a light making it easy to see the speedometer cable and plan your attack.

Swapping the cable out is easy and several online vendors have em. NAPA may be a good source if that's an option.

Before you buy a new cable, disconnect the old one at both ends, attach a small drill motor to the tranny end of the cable and have someone spin it while you watch the speedometer end. Hopefully it won't spin meaning a simple cable replacement will solve the problem.

Also, lots of reading available on how to best service the speedometer. Me, (despite advise to the contrary) I occasional squirt a bit of WD40 into the back of the speedometer head. This quiets things down and smooths out the jumpy needle. I did replace the cable a couple years ago and 4,000 miles later all's still good.

Good Luck, RonR

Last edited by moparguy; 07/07/2018 12:40 PM.
RonR


1951 3600 with Clark flatbed, T5, 4.10 rear
1970 340 Duster
1990 5.0 V8 Miata (1990 Mustang Gt Drivetrain)
1964 CJ5