Speedometer
 

Took the 68 out for a drive yesterday and around 50 mph the speedometer began jumping, went to pointing straight down and made a whining noise. Slowed down and it stopped, sped back up and it resumed the previously described behavior. Pull into to a parking lot to turn around and resuming my journey home the needle stayed steady at 50 and no noise. Odometer worked at it should during this. The transmission is a 4 speed Muncie.

I'm thinking the cable may need lubricating. Anyone else experience this or have suggestions?

Thanks in advance

Stop driving the car, the speedometer is well past it's designed in life cycle and it needs rebuilt. A dry or worn Cable can and will make the pointer jump and/or bounce but it would never move the pointer past 120 MPH. Only a desert/dry-worn out bushing inside of the speedo head would do that.

You can disconnect the cable from one end and keep driving until you can do repairs.
Peter Serio rebuilds speedometers (previous poster)

If it gets too ruined it might get beyond repair.

Would pull the cable off the car and go over it too .
Most cables will let the core come completely out from one end.
Recommended not to have any grease for the last 5-6 inches nearest speedometer.

I have formed a triple layer of aluminum foil over the transmission bung where cable attaches , then put a hose clamp around it. To keep driving with cable off.

I lubricated my speedometer cable on my 69 just to be on the cautious side. I disconnected the cable behind the speedometer and pulled out the inner cable. Wiped it down with brake clean and inspected it. Then lubricated the cable with a speedometer lubricant I bought from my local auto parts store. As mentioned above, leave several inches of dry cable at the end nearest the speedometer head. The service manual even mentions this too. If this doesn't work, as Pete mentioned, it is in the head and needs a rebuild. Good luck!!

Thanks for the suggestions, I'm going to try the lubrication and inspection that Baron and Ram Air suggested to see if that resolves my immediate issue. If not then Peter I'll be in touch about a rebuild.

Thanks again !!

If you dont have the special lubricant that Jack suggested ,
I use synthetic wheel bearing grease.

Just try not to use anything like white lithium grease that will dry out in a few years or so , on cars not frequently driven.
You would just have to repeat the cleaning out and lubing in shorter time.
Good Luck

I pulled the old cable and housing out of the car and the cable was really snug in the cable, pulled it out and it had a couple of "rough" areas so I bought a new cable and housing. Installed it today and that solved my noise and bounce issues.

Thank you for your responses and suggestions. It is appreciated.

That was definitely worth a punch hole in your Lucky Guy card.
Glad you got it all fixed up
Congrats