Speedo Inaccurate

[dannyk11135]

Hey guys, I have a 1997 k3500 diesel. Speedometer is very inaccurate. It is more accurate at lower speeds, but gets progressively worse. At an actual 3mph it’ll read 5, then at 10 it’ll read 15, at 45 it’ll read 50, but once we started getting into the realm of 60, 70, 80, the truck reads 10-15 mph too fast. 4.10 gears, new tranny, new (correct) DRAC, new VSS, and the diameter of the tires is only like .1” bigger than original that I just disregard tire size being the issue completely. New cluster? Can I fix the cluster somehow? Anything I’m missing? Thanks

 

[scott2093]

New cluster?

Maybe. Pretty close early on.... Can you get a scanner to see what the computer is saying the speed is and compare with gps speed? If they're good, most likely speedo.
Someone else will have to speak to repairing it.

 

[dannyk11135]

Maybe. Pretty close early on.... Can you get a scanner to see what the computer is saying the speed is and compare with gps speed? If they're good, most likely speedo.
Someone else will have to speak to repairing it.

Checked my scanner, and the vehicle was calculating the correct speed; verified it to a GPS speedo. So, cluster speed is just inaccurate.

 

[SUBURBAN5]

Leaning towards you need a new cluster. Info can be found by downloading service manual.

 

[SUBURBAN5]

If you get another one just fyi it's 50/50 to be better or worse. Gm clusters have a bad rep minus the z56 cluster. If you seek another one just make sure it's diesel..

 

[dannyk11135]

If you get another one just fyi it's 50/50 to be better or worse. Gm clusters have a bad rep minus the z56 cluster. If you seek another one just make sure it's diesel..

what exactly is the Z56 cluster?

 

[SUBURBAN5]

what exactly is the Z56 cluster?

Police package cluster. Pretty much anything "certified"

 

[SUBURBAN5]

Thread '100 MPH Certified and 130 MPH Certified Clusters' https://www.gmt400.com/threads/100-mph-certified-and-130-mph-certified-clusters.44772/

Little more info

 

[dannyk11135]

Police package cluster. Pretty much anything "certified"

they make em in diesel?

 

[SUBURBAN5]

they make em in diesel?

If they do it's a unicorn. I can't find any info of a Certified diesel cluster