This new speedometer driven gear fits C4 C5 C6 C10 FMX AOD transmissions. Will work with 3.25 OEM number: C1DZ-17271-A Based on 25.4" tall tyre Will also fit T5 Tremec T45 T56 Magnum and TKO manual transmission Tech Tip: If you can determine whether your speedometer is reading too slow or too fast, it is worth noting that a lower # of teeth will cause it to turn faster versus a higher # of teeth to turn slower