I got a gauge cluster for my 90 vert from a junkyard, the speedometer was an 85mph. I put a silver faced gauge kit in with a 140 speedo, does any one know what to recalibrate it or better yet a shop I could take it to? Also what exactly is the diffrence between the 89 and 90 and gauges?
The '90+ cluster is pinned different in back, it won't just plug in to an '89 harness, and vise-versa. Also, it looks a little different; the gauge faces don't come down as far, because the '90+ have the airbag. To get it right you'll need to change your speedo gear at the tranny, or send the gauge out to be recalibrated. I believe Brothers Performance does it for about $40. The gear on the other hand, should only be $10-$20, and it's relatively easy to replace yourself. Call Hanlon Motorsports for the right gear, they will know which one you need and probably have it in stock.
North Hollywood Speedometer did the recal for my Saleen 200mph Speedo, cost $60 with 2 day shipping to and from.
Changing the gear in the tranny or the speedo cable will not correct the speedo from a 85-140, although it should be matched to your current rear gear ratio.