I am going to need to recalibrate my speedo soon as I will be putting a different tire size on my truck. It is an 89 F-250 7.3 diesel 4x4 with the ZF-5 speed manual transmission and 4.10 gears. Where is the best place to get a speedo gear for this? Are the gears different for the auto vs manual trannies? (It looks like the gear is actually in the transfer case on my truck anyway). Also what is the proper formula to use for calculating the teeth on the gear I need to get?

Local auto parts stores didn't have it and it looks like Summit only has it for mustangs with the ford AOD and Tremec T-5 and stuff.

Thanks

 

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You can still get these gears at the dealer. I got a 21 tooth for around $2 and they even had it on the shelf. The driven gears are different between automatic and manual transmissions. I'm not sure what transfer cases use, but I would guess they would be the same as the manual transmissions.

I used this website to determine what gear I needed and compared that to what I already had: Ford Bronco Speedo Gearing