I have a 1984 F250 4x2 6.9L Diesel with factory speed control, aka cruise control. The speedometer has had a mild bounce for years and last fall the cable finally gave way. The lower cable end was broken at the speed sensor just below the brake booster and well overheated (outer sheath melted) near the exhaust. I replace the broken cable - LMC who got it from Dennis Carpenter NOS. The cruise is working again but the speedometer was still bouncing. I disconnected the short upper cable at the speed sensor to lube it up. I can freely spin the upper cable by hand either direction but after 10 to 15 revolutions it binds up and gets a little stuck. A little twist with pliers gets it past the stuck spot for another 10 to 15 revolutions. I lubed more, coaxed the lub down the cable with air, more lub, hand drill at moderate speed, more lube, rinse and repeat. Still, rotating by hand is very smooth for those 10 to 15 revolutions until it sticks. Past experience leans me toward the speedometer in this case since the cable spins freely so many revolutions before getting to the bind.

Is the likely culprit the cable or speedometer?

 

Have you pulled the core from the upper cable for an inspection? I bet you will find it birdcaged. Just disconnect it at the speed sensor and use needlenose pliers to pull out the core.

If still unsure, I’d inspect the cable first simply because it’s much cheaper to replace.

If you find it failed, you can replace the core with one of those universal kits. They have one end already swaged square. You cut the other end to match the old core and use the included “anvil” to square off the cut end with a hammer.

 

UPDATE: It's the speedometer. I pulled the cable and it is fine, spins freely, gonna coat it down with graphite spray prior to reassembly.

As for the speedometer, Inside the barrel to which the cable clips it binds up. The odometer is working perfectly too. I bet it would be fine if I could get it apart, clean and lube it. Anyone know the secret to separating the needle shaft from the rest of the speedometer.