Speedometer gear?

[Slacker809]

I have a t-18 and running 4.10 gears. What speedometer gear do I need? I have to replace cable and figured I'd try to get speedometer correct.

[mrtleavitt]

Can't really just look up in a book and find the best gear from my experience. Depends on tire size, existing gear tooth count and how far off your current speedo is. I did a lot of calculations and gear swaps to get my speedo dead on. Let me see if I still have my research saved on my computer.

[Ren]

Here's what I would try: Borrow a vehicle you are reasonably certain has an accurate speedo. There are a number of simple ways to determine this to your satisfaction.

Drive borrowed vehicle exactly one mile as indicated on the odo from your driveway. Mark the spot. Do the same thing with your vehicle. Note the difference in odo readings.

Let's say your vehicle reads 9/10 of a mile. This is 10% slow.

Determine how many teeth the driven speedo gear in your trans has. Let's say it has 17.

That gear needs to spin 10% faster than it is doing. That means it needs fewer teeth.

17 - 10% = 15.3.

Go online and find a speedo gear with 15 teeth.