Speedometer cable showing less than half

[Darstrom]

I recently replaced my speedometer cable since the speedo was bouncing a lot.
Now the problem is that it's showing less than half speed.
Took out the speedometer and checked it, seems to be working fine.
And from what I can tell the gearing for the cable is inside the gearbox?

Truck is a GMC Jimmy 1979 4x4 manual transmission.

It's running on 33" tires, but was before as well and the speedo was showing more or less the correct speed.


Anyone got any idea on what to do?

 

[Bextreme04]

the speedometer should be coming from the transfer case output not the gearbox, right? Did you remove a little box in between the speedometer and the transfer case? It's also possible that you have a bad speedometer.

 

[Darstrom]

Yes my mistake Bextreme, it's coming from the transfer case.
I do not have a box in between, but I suspect there should be something or perhaps an extension since the cable is really tight around the corner in other words way too short. And that is with the longest cable available for these models appearantly..

Is there a way to tell if the speedometer is bad except for getting a new one of course?