Speedometer gear

[87silveradok20]

Alright guys so I need to make my speedometer accurate in my 1989 v3500 crew cab dually and I’m having trouble finding reliable information on the gears. What I have is a light blue gear in the transfer case and the gear that comes out is black. I have 4.10 gears (at least that’s what the glovebox says) and 31.6 inch tall tires. What do I need to replace the black gear with to get my speedometer close. I’d rather not replace the light blue gear but I will if I absolutely need to. I don’t care if the speedometer is a little off but right now it’s 20 mph fast at 55


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[Craig 85]

Here's how to check for what you need. Scroll down to Mechanical Ratio Adapter. I know my K30 has an adapter on the transfer case and so did my '79. The funny thing was my '79 had 3.08s prior to the 3/4 ton axle swap to 4.10's. Same height tires. I was able to remove the factory adapter and plug the speedo cable right into the transfer case and I was within 5% accuracy.

http://www.bobsspeedometer.com/1/120/ratio_adapter.asp