My 1991 245 had the rear-axle replaced by the previous owner, but was replaced with one from a 1992 24x. As such, the speedometer climbs up to max speed by the time I am going 30 mph. Just coasting down the street causes the speedo to climb from 0-80!

The needle doesn't jump...it's pretty smooth, it's just rising to a speed that's way too fast! The odometer works too (surprisingly), but of course, is racking on more miles than really are being driven.

I'm guessing there is a sensor mismatch in the rear axle, and have read that there are greater/less teeth in the rear-end for each model year/different options.

Is there any sensor I can replace, or anything to configure/switch to make the 92 rear end match the proper speed on the speedo? Or, is the only option to pull the rear axle or swap out the speedo from a 1992?
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Adam
1997 850 Wagon Auto
1991 240 Wagon Auto
2004 Saab 9.5 Aero 5sp