Speedometer jumping

[dgrinnan]

I have the original speedometer in my 47 WC 1/2 ton.  Original transmission.  I have a new speedometer cable.  When I first hooked it up it was working but frequently bouncing around a 10 MPH fluctuation. Mostly jumping between correct speed and 5-10 MPH faster than my actual speed.  Annoying but I didn't pay that much attention to it.  I went for a ride yesterday and it was spinning wildly the full range of the speedometer.  It eventually settled down and went back to the 5-10 MPH bounce.  I could here "growling" from the speedometer when this was happening.  I have seen similar post and the diagnosis was the cable needed to be lubricated.   That should not be the problem here considering it is a new cable.  Could it be as simple as the a shot of WD-40 in the speedometer?   Is the speedometer on it's last leg? 

Edited December 2, 2023 by dgrinnan

[Young Ed]

There should be a little wick at the back of the speedometer to oil that too. Also not sure I would assume that the cable is well lubed just because it's new. Did this problem getting worse coincide with a drop in temp? They may have used something that's too thick for cold weather

[dgrinnan]

It was about 50 degrees when I took a ride.

[nonstop]

My car and truck did the same thing.  I found the wicks for the Speedo, cleaned them and used light oil or even engine oil in a pinch (not recommended) and it solved the problem almost immediately!

[B1B Keven]

1000 wt liquid silicon for radio control car shocks works best.

There might be some crud between the magnets and speed cup.