Slow Speedometer and Odometer

[Chuck]

The speedometer and odometer readings on my newly restored 1929 tudor are about 50% of what they should be compared to my GPS.

I would appreciate any suggestions on a solution.

Thanks,

Chuck

[Modelakid31]

Did you change any of the gears in the rear end?

[Bob Johnson]

First check that you have a MPH and not a KPH (Kilometers) speedometer. Look at the 0 on the speedometer, is there a KILO in the center of the 0?

If you do not have a KILO speedometer then the only thing I can think of is that your rearend, tires, speedometer gear in the driveline are incorrect.

Bob

[Chuck]

I have a 3.54 differential and a 17 tooth speedometer gear with 21 in tires.

[Mike V. Florida]

I believe that 3.78 is standard rear end. The 3.54 is a high speed rear end.

A 17 tooth gear is needed for 21" tires and your cars rear end.

[Patrick L.]

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It appear your drive gear is correct.. I'm wondering about the settings on your GPS.. Kilometers 58% to MPH and Knots are 15%..

[Tom Endy]

My thoughts are that if the error factor is 50%, the problem is not gear ratios, but possibly a faulty speedometer.

Tom Endy

[Chuck]

I finally found the problem. The square end of speedometer cable I purchased from Cushman Speedometers was too short and was not completely engaging the speedometer. I purchased a speedometer cable from Snyders and it works perfectly. See picture to see the difference in the length of the square end. The gold colored cable was from Cushman and the black colored cable was from Snyders.