How will a change from a 3.08 to a 3.73 affect my miles on odometer/gas mileage? If it takes more rotations of the drive shaft per one rotation of the wheel then this will result in higher engine RPM which results in higher odometer turns.

Is this correct?

In other words what I'm asking is going from point A to point B with a distance of 10 miles, the odometer would now read 10 miles travelled. Once this gear swap is completed, going from the same point A to point B will register as (not precise#, just an example) 13 miles? I would therefore be cheating myself out of some miles which will lower resale value. (Speaking theorically since I would never sell my very 1st Ford truck )

If the above assumption is correct, how to I resolve this issue? Is the odometer connected directly to the engine or the drive shaft or what?

 

Depending on the year of your truck the speedo can be recalibrated either mechanicaly or through the computer.

If you search this subject you'll find plenty of info.

Good luck.

 

Thanks Le Pew. I did do a search and came up with plenty of hits about Superchips but nothing answering my question about the number of miles.

 

Yes, your odometer will read more miles travelled than you actually went falsely indicating better MPG. My 97 couldn't be recalibrated via computer at the dealer. I had to swap the speedo gear. I think the rule is if you have a digital odometer then the computer can be reprogrammed.

 

Lean & cut;

The change to your indicated mileage would be in increase of (3.73 / 3.08 ) or 1.211 times, or 10 miles x 1.211 = 12.11 miles. This is a percentage change of 121%. Yes you are adding mileage to your odometer that you haven't travelled. Depending on the year of your truck, you could change the VSS gear in the transmission or you may have to have your computer recalibrated. I was lucky and was able to change the gear in mine when I did it. Let the good members know what year and model you are driving and the best solution can be found. As far as gas mileage is concerned, I changed from a 3.08 to a 3.55 in my V6 5-speed and my mileage was no worse and was better under some conditions. Glenn McMullin.

 

Thanks Davet and Glenn.

My truck is a 99 V6 5 speed. Does this mean I should talk to Mike Troyer? LOL. I still haven't order a Superchip yet, just been putting it off because I wasn't sure about the soon to come changes.

It's a good thing I procrastinated because I finally found a brand new complete Ford rear end (many thanks to JMC!) which will be installed new weekend. Total cost of swap should only be 2 grand and this includes new differential, aluminum drive shaft, master cylinder, fluid, miscelaneous parts, and labor (done by Ford master tech)

Should I wait until after getting new heads to get a chip. I've read you need a reprogram for that too.

 

The gear for mine was $18.00 from Ford and I changed it myself in about 15 minutes. I had called several dealerships and all said I needed to have it done with a computer change. I was quoted from $25.00-$100.00 for this. After my local dealership spent 3 hours trying to load a new speedo setting into my non-programmable computer they told me I needed the whole electronic VSS assembly in order to get the gear. Because of info I learned here I located a knowledgeable local dealer that knew about the separate gears available and they had them in stock.
I can't say if you should get a chip or not but these are the costs of the speedo correction if you decide to wait on the chip.
Good luck.

 

So when I go to the dealership I should ask for a "speedo gear"? Could you post instructions on how to change it please.

Also, what year is your truck? I wonder whether mine needs a speedo gear or just the chip. I'm planning on putting in a new instrument cluster (including tach which I don't currently have), is this where the speedo gear goes? Maybe I can do both at the same time.

 

No gear for you, yours is a 99 so it must be done through the computer or with a chip/programer. Gears are for 97 & 98 model years.