changing gears in my diffs?
Junior User
Joined: Jun 2018
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When you change gears, your speedometer will be out of calibration. Depending on the vehicle, sometimes that can be fixed with a programmer or sometimes you need to put in new gears. That's one thing I liked about having my GM car from over 15 years ago. I could put in a new gear and use a Hypertech Power Programmer to tell the ECU which gears I was using as well as the tire size so that the speedometer would be correct.
Junior User
Joined: Jun 2018
Posts: 53
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That's awesome. I remember having to put new gears in a Mustang after having the rear end gear changed to a 3.73. I like programming much better.
Moderator
Joined: Jul 2010
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From: Media PA
Correct, the tone ring for the speedo sensor is on the rear's ring gear, so new deeper gears will not affect the speedo. The ring gear spins at the same rate as the rear tire, deeper gears only make the pinion spin faster. Bigger tire's will throw the speedo off to read lower than actual, that is based on tire revolutions per mile, which can be adjusted in the PCM by the dealer or some tuners. Going from 3.73s to my 4.88s didn't affect the speedo at all, when I swapped out the 31.6" tires for the 35"s has the speedo reading 12% low.
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