How to figure out the Speedo gears.
 

Can someone explain how to determine the proper speedo gears if changing rear axle gears. I have the 402/th400 2wd with 3.07 posi & 29" tires (275-60-15), and I believe the speedo is correct now. I'm thining of going to a 3.42 ratio, but all the other stuff with stay the same. This will cause the speedo to be off one way or the other.

I keep meaning to put the GPS in the truck and check the speedo, but you know.....

Re: How to figure out the Speedo gears.
 

I think bowtieoverdrives.com has shows exactly what kind you need

Re: How to figure out the Speedo gears.
 

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Here are a couple of sites that have calculators...

http://www.bgsoflex.com/speedo1.html

http://www.transmissioncenter.net/sp...n_______va.htm

LockDoc

Re: How to figure out the Speedo gears.
 

Thanks, Will check them out.

Re: How to figure out the Speedo gears.
 

Here's a site I used. http://novaresource.org/speedo.htm
Also, here's a short write up I did. http://67-72chevytrucks.com/vboard/s...56#post3347056

Re: How to figure out the Speedo gears.
 

Great info, Thanks.