Speedo help please
 

79 c10 th400. have green 20tooth drive gear and white 36 tooth driven gear. 27in tire 3.73 rear. calculator says I need 54 tooth driven. every that sells them only go to 45 tooth. how hard is it to change the drive gear?

Re: Speedo help please
 

Changing the drive gear can be a lot of fun.
You gotta drop the driveshaft, tranny crossmember and remove the tailhousing of the tranny.
Then pull the gear, swap it out and put it all back togethor.
I’ve always cheated.
Bypassed all that work completely.
I use a ratio adaptor that fits onto your speedo cable.
Like here. They have calculators too.

https://transmissioncenter.net/?swoo...-gears&paged=1

Re: Speedo help please
 

Ratio adapters wear out faster than plastic gears.
I dont trust the calculators either.
The GM tables are in the parts books. You need your tire size, axle ratio, and transmission gives you the correct gears.

Re: Speedo help please
 

Not Sure if you are looking to stay 100% stock? I went with a GPS Speedo when I did an LS swap. Very easy, plug and play. Eliminates speedo cable and you wouldn't have to worry about tire size or gears. Just have to modify gauge cluster.

Re: Speedo help please
 

Now that is cool.