Speedometer reads way too fast

[AJM008]

What is the stock tire size on the door jamb label and what size tires are you running? Has the rear axle been changed versus what it came with stock?

For a 1998, GM says that a 4-mph error is within spec.

Speedometer inaccurate:

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The tire size is the same as the door jam, and I have no idea if the axel has been changed. But from reading this chart. I will be replacing the cluster. Thanks!

 

[Kirk]

My '98 C3500 has always read 4 mph fast with my GPS's, but about 15K miles ago it start reading 9-10 miles faster! I'm the original owner and have always run with the same stock tires and original rear end, not sure whats going on there! Just ordered a replacement dash panel and hoped to fix this problem while I make the change, I'm clusterated.

I ordered an ODB2 reader maybe it will confirm the censer.

 

[Kirk]

I used an ODB2 reader with Dashcommand, and confirms the speedometer and temp gauges are faulty. I will be replacing the cluster. Where to find a reliable will be the key.

 

[Ike98silverado]

Just got a used one 100% tested on ebay $60 free shipping

 

[Kirk]

How happy are you with it? Could you post the link if it’s performing?
Thanks


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[slovcan]

Hi folks,

OK, about these clusters with the speedometers reading way higher than they should. I have determined that my speed sensor and odometer match my GPS (speed via the OBDII port). That seems to be the "they all do that, sir" problem of the speedometer itself. It also seems the solution is to replace the cluster.

So, question 1) At what mileage does this problem generally rear its ugly head? Mine was doing it when I get it at 239,000 kms (148,500 miles). It hasn't changed in the past 41,000 kms. I have a replacement on the way with 144,000 kms on it (89,500 miles). No returns allowed.

Question 2) What are my odds that this will be a good one?

Question 3) Is there a how-to somewhere that I can follow to move my odometer over from my current cluster to the replacement?

Thanks all,
Glenn

 

[kennythewelder]

Hi folks,

OK, about these clusters with the speedometers reading way higher than they should. I have determined that my speed sensor and odometer match my GPS (speed via the OBDII port). That seems to be the "they all do that, sir" problem of the speedometer itself. It also seems the solution is to replace the cluster.

So, question 1) At what mileage does this problem generally rear its ugly head? Mine was doing it when I get it at 239,000 kms (148,500 miles). It hasn't changed in the past 41,000 kms. I have a replacement on the way with 144,000 kms on it (89,500 miles). No returns allowed.

Question 2) What are my odds that this will be a good one?

Question 3) Is there a how-to somewhere that I can follow to move my odometer over from my current cluster to the replacement?

Thanks all,
Glenn

This video will give you an insight into what all is in the cluster, and how to take it apart. As for the speedo or anything else in there going out at a certain point in time or mileage, no not really. There are a ton of variables that effect the life of any component.

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[slovcan]

Thanks Kenny. I'll study the video.

Cheers,
Glenn

 

[Dariusz Salomon]

Mine is reading 35 at 30mph,47 at 40,58 at 50,70 at 60 and 82 at 70. 103000 miles-had smaller wheels(diameter) for a while-I don't know how long. Changing wheels to about regular diameter made no difference whatsoever. I drove for a while with gps on until I memorised these numbers.

 

[east302]

Question 3) Is there a how-to somewhere that I can follow to move my odometer over from my current cluster to the replacement?

Thanks all,
Glenn

Here’s a link that should help with the odometer:

https://www.gmt400.com/threads/changing-mileage-odometer-cluster-swap.46145/

Per GM, a speedometer reading within 4-mph of a GPS was within spec.


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