Need help with speedo gear after rear end gear change
 

Can somebody help me with changing the gear on the speedo cable at the Transmission after a rear end gear change. The truck as a 700r4 and I had a 3.07 rear end and this weekend I had it swapped to a 3.73posi and my speedometer is now about 10 miles an hour off.what is the best way to figure out what gear I need to change to on the transmission

Re: Need help with speedo gear after rear end gear change
 

Here is a link to TCI's page. They walk you through it pretty much, but you have to figure it out based on what you have and how you want to change it.

http://www.tciauto.com/tc/speedometer-gear-calculator/

Re: Need help with speedo gear after rear end gear change
 

I usually just add an external mounted ratio adapter of the percentage required, like these: http://www.partshp.com/speedometer_gears.htm

It "skips to the end", bypassing the math and any detail measurement errors regarding tire rolling radius and such.

When I switched out the "Slim Jim" for a TH400 in my '63 Grand Prix the adapter I needed was already laying out on the workbench.

K

Re: Need help with speedo gear after rear end gear change
 

X2 on what Keith S. said with the gear ratio adapter. He guided me to the same website when I had a similar problem going from a sm465 granny 4spd to a TH350 auto. Had a 3:07 rear axle ratio in my '71 4x4 and I ordered an "off the rack" ratio adapter speeding up my speedometer. Easy install, 15 minutes while I drank a cold Bud. Speedometer is dead on exact using our Garmin GPS. HIGHLY recommend looking into the same fix.

Thanks again for your help, Keith. :chevy:

Re: Need help with speedo gear after rear end gear change
 

Just throwing this out there as a quick fix. I have a portable garmin gps, it's got a speedo built in that runs off satellites. Costs around 100 bucks and there's no monthly fee. Might keep you from getting a ticket till you can get this figured out.