What is the actual difference (or what makes the speedo) be a 120 or 140 MPH speedo? Is the mechanics (this is the electronic speedo not the mechanical "wire" driven one) used in 1989 etc.

The face of course is different with 120MPH or 140MPH is the actual mechanics the same underneath or is there a difference?

Also is there a way to change the milage on one (my 140MPH speedo has something wrong with it and I have a 120MPH unit with the wrong milage I can either swap the mechanics out if they the same or transplant some parts to make my 140MPH work again).

Any help is really appreciated.

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12-23-2005, 01:45 AM

Kevin91Z

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Car: 1990 Pontiac Trans Am

Engine: 355 TPI siamesed runners

Transmission: Tremec T56

Axle/Gears: 12-Bolt 3.73

I know you can remove the entire speedo unit and replace it with another entire unit. And the mechanicals are what set the speedo with the numbers indicated on the faceplate. But I have no idea what is wrong with yours or if you can fix it with parts from another unit. Good luck.