Quote Originally Posted by 88stepside View Post
Check these out:
http://www.fullsizechevy.com/forum/a.../t-155414.html

http://www.chevytalk.org/fusionbb/sh...hp?tid/258562/

Basically, back in the day before DRACs and VSSBs they had the speedo "settings" for tire and gear inside the cluster. The way to change them is not hard once you know how.

I still have the parts in my garage, I'll dig around tommorrow and see if I can find the part numbers.

The second link has a great way to replace factory "clip" with a dipswitch.
25085515 and 25084374 are the GM parts we used to use to calibrate 88-90 C1500 speedometers. Hope this helps.