Speedometer Gear

[lub997]

I swapped transmissions in my 1990 2WD 2.3L Ranger a while back and put in a newer one from a 1997 Ranger that was also a 2WD 2.3L model. Both the old transmission and the new one are the M5OD 5-speed overdrive manual transmission. Although this swap was done quite a while ago, I am just getting around to putting the correct speedometer gear in, to get my speedometer reading correctly again. The original speedometer gear was a black 20 tooth. After the swap, it was reading exactly 100 km/hr when a GPS said it was going 70 MPH, so that means it was going 62 MPH when the GPS said it was going 70; a difference of 8 MPH. So, I tried a white 17 tooth gear, and that got me closer, but still not enough. With the 17 tooth, my GPS said I was going 5 MPH slower at nearly every speed than the speedometer was reading. So, I recalculated, based upon observations with the more accurate, but still not quite right 17 tooth gear, and came up with the result that the 18 tooth should be just about perfect. So, I tried a yellow 18 tooth gear today, and it was off by about 2-3 MPH at slower speeeds, and only off by 1 MPH at 70 MPH. When it said I was going 70 on the speedometer, the Garmin GPS read 69 MPH, and I was keeping the accelerator very steady on flat level ground on the interstate. My question is, can I achieve greater accuracy than that, or is this as good as it originally would have been from the factory anyway? 1 MPH is not a big deal to me; but I do want it to be as accurate as I can get it.

 

[06RangerXLT]

most speedos are off by about 4 to 5 mph. also if your tires arent what came with the truck it will be off. so every time you change tires u will have to re calculate

 

[lub997]

That's good news! I'm glad I can finally be satisfied that it is at least as accurate as it originally would have been. Thanks for the info!