Speedometer jumping all over? 91 K5

[Jessie James]

My maiden voyage of the new truck and about 20 minutes in the speedometer starts jumping around like crazy. While I'm doing about 65, it's going anywhere from 35 to 85. Is this a loose wire, bad VSS, bad speedo, or do I need to dig in deeper?

 

[scrappy88]

I would start with the cable and also while you're doing that I suggest oiling the bushing on the speedometer where the cable connects. Mine did the same thing and it was a combination of the cable and the bushing that needed lube. Now it's smooth at any speed.

 

[tRustyK5]

91 doesn't have a cable. It's an electronic speedo...and I have no idea what would make it jump around.

Rene

 

[digs]

My 91 did the same thing. I went looking for loose connections and cleaned a few greasy connectors and the problem went away. I cant say that I fixed it but it's been good for a few months now.

 

[Jessie James]

I wish I had bought this truck in the summer time. Working in the cold sucks!

 

[Russell]

I'd suspect the sensor in the tailshaft of the t-case first, then the DRAC, and the speedometer itself last. Of course, as mentioned, check all your connections first. Pretty robust system all around!