Found reduction/speedup box for TBs!

[vader87]

Found a place on line that sells gear reduction or speedup box for our speedometers. I am a little slow when it comes to math so here it is:

Running the 200 tansmission with 28 inch tire and 3.42 gears.

While traveling 74 MPH, my speedo reads 60. A 20% speedup will get me close to where I need to be. I have a 145 mph overlay that I would like to install so what percentage slow down or speed up box will I need?

Here is the link:
Speedometer Gears, Speedometer Gear, Ford, GM, Dodge 700R4

 

[mikestertwo]

Running the 200 tansmission with 28 inch tire and 3.42 gears.

While traveling 74 MPH, my speedo reads 60. A 20% speedup will get me close to where I need to be. I have a 145 mph overlay that I would like to install so what percentage slow down or speed up box will I need?

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I would put the overlay in first before you calibrate the speedo. Remember when you put the overlay in and calibrate it, the speed the computer sees is going to be off. To get your stock speedo calibrated, assuming your numbers are correct, you need a 1.23 gear box.