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Out of whack spedometer

I drive a 2003 Chevy TrailBlazer. Whenever it’s driven on the highway where the speed limit is higher, the speedometer needle slowly moves forward until it appears that I’m driving over 100 miles an hour (but I’m not!). After a few days of normal, suburban driving, it gradually goes back to normal and registers the correct driving speed. Why does it do this, and what can I do to fix it? The car is in otherwise good running order.

Does it affect your cruise control? Not knowing a whole lot about Chevys, I could maybe suggest having the rear end checked. Some manufactures use a sensor similar to that of your ABS, but this is a ring attached to the ring gear in the differential instead of the wheel end. My theory is that there is some metal particles that have become magnetized and stuck in notches on that ring. When you slow down, the oil is allowed to drip down over it “washing” these particulates away. Just a theory…

You need a new instrument cluster. Very common problem on your truck. GM extended the warranty on its full size trucks, not on the Trailblazers. The repair runs a little over $500 at the dealer, most big cites have repair companies that can fix the cluster for a little less.

Dorman makes a replacement or remanufactured instrument cluster for your TrailBlazer for less then $200.00. here is a link http://www.rockauto.com/catalog/x,carcode,1412277,parttype,602