Speedometer Gears

[texasmike]

I have just about decided to change from a 2.73 to a 3.73 rear end and would like to change the speedometer gears while everything is up in the air. Does anyone know how to figure out what gears I would need to buy and where I can find them? I have a 700r4 with 225/75 R15 tires (28.3" ht.).

 

[Bextreme04]

There are several ways to do this. The 700R4 has multiple drive gear and driven gear options. You need to know what current driven and drive gear is in the transmission. Then you need to know if the current speedometer is even accurate. I would suggest you download a GPS speed measuring app to your phone and go for a drive at dead on 50mph on the speedometer and see what the GPS says you are doing. Once you know what the current driven and drive gears are for the current setup, you can calculate exactly what drive and driven gear are needed to make it accurate with a gear ratio change.

They sell a whole array of gears for this as well. https://www.amazon.com/dp/B084BW8H82/

TCI has a nice calculator for you to figure out what driven teeth you will need for a given drive tooth, axle ratio, and tire size.
https://www.tciauto.com/speedometer-gear-calculator#700R4

 

[texasmike]

Wow, that's a lot of good information and just what I needed. Anyone with a SB is really missing out if they don't visit this website. You guys also exhibit a lot of patience with us shade tree old man mechanics. thanks!!

 

[Matt69olds]

This will help calculate the gear needed

TCI Auto Speedometer Gear Calculator - TCI® Auto

Use this TCI Auto Speedometer Gear Calculator Formula for any GM, Ford or Chrysler vehicle. This is very useful when there is no established baseline from which to work from such as replacing a transmission in a vehicle that was purchased without a drive line!

www.tciauto.com

 

[Juggernaut]

Speedometer Cables USA - Gear Box Adapters

Speedometer Gearing Adapters for Light and Heavy Duty vehicles, OTR and Industrial Vehicles

speedometercablesusa.com