Speedometer pinion selection

[threewood]

62 Plymouth, 727, 3.23 741 rear gears, P195/75R14 tires (25.5"). I have the green pinion in it, 20 tooth, which should be correct but is not. Speedometer shows 9mph high at 60mph. (Driving GPS verified 60mph, but speedo shows 69mph).

Do I need a higher tooth or lower tooth pinion to get it right?

 

[R413]

More teeth slow the speedo down.

 

[Jam72]

62 Plymouth, 727, 3.23 741 rear gears, P195/75R14 tires (25.5"). I have the green pinion in it, 20 tooth, which should be correct but is not. Speedometer shows 9mph high at 60mph. (Driving GPS verified 60mph, but speedo shows 69mph).

Do I need a higher tooth or lower tooth pinion to get it right?

More teeth to slow speedo reading down. If your pinion is correct for the tire and differential combo, perhaps it is a speedo calibration problem.

 

[lewtot184]

A 21 tooth will get you a 5% reduction. A ratio reducer is another option but expensive. I really think something else is wrong. Try a tachometer and do the math on engine rpm/speedo reading.