Speedometer question

[7900_Blazer]

What would cause the speedometer to only start working at say 30 or so.. and jump around and at 60 mph, it only shows 45 or 50?

Is it most likely:
1. the greased up super dirty speedometer cable
2. something in the transfer case
3. the gauge?

Thoughts?

 

[squarelyfe]

Probably a partially worn speedo gear, inside the tail shaft. It's plastic and wears out. Could also be worn at the other gear that enter from the side.

 

[7900_Blazer]

@squarelyfe thank you!