Engine/Transmission (1994 - 1998) Speedometer/Odometer Error

[AlMoore]

I have a 97 2500. I had the rear end rebuilt and had the 3.54 gears dropped to 3.73. I have a speedometer error or about 6 mph and an odometer error or approximately 9 miles/100. At 60 mph the speedometer indicates 66 mph approximately according to my GPS. The gear on my vehicle speed sensor has 31 teeth. I need to know how many teeth I need on a new gear to correct the error. I also saw a paragraph in one of the TDR magazines talking about a capacitance type fuel quantity transmitter, but I was not able to find the paragraph again. Does anyone know about this item and if it is any good. On aircraft they use capacitance fuel quantity transmitters,
but I know they are sensitive to water. I also need input on how to get the VSS gear out of the housing or if it comes out at or if you have to get the gear/housing assy.

 

[RustyJC]

It's a ratio equation. 3.54/3.73 = 31/x, so x = 32,66 (round to 33 teeth). Now, having said that, you must have had a ~4% error before the axle ratio change because the speed and mileage are reading 10%/9% high respectively, but the gear ratio change was only 5.4%. If you want to change the speed and mileage 10%, then the gear would need 10% (round to 3) more teeth, or 34 teeth. So a 33 tooth gear should get you close to where you were before the axle ratio change, but a 34 tooth gear should get you closer to your GPS readouts.

The above assumes that you're talking about teeth on a driven gear, like the gear at the end of the speedometer cable that goes into the transmission or transfer case and is driven by the output shaft. If it's a drive gear, please advise as the number of teeth would have to be reduced and another calculation would be required.

Rusty

 

[AlMoore]

Thanks Rusty, That was about what I had concluded, that three teeth would get me to more accuracy, Yes the speedometer was off a bit before the rear end gear change. Do you know,does the driven gear come out of the housing or do
you have to change the gear/ housing assembly?

 

[GAmes]

There is an exploded diagram of the VSS in the factory service manual. Yes, it completely disassembles.