Where to find a speedometer calibration box?

[chastain90]

I didn't know a new speed calibration box would be this hard to find. I need one to compensate for 33 inch tires. Any sources?

[dirish]

Try flexibledrive.com
Or bobsspeedometer.com

[Ironhorse]

I had great luck with using a speedometer adapter from www.tciauto.com. I was able to order an adapter from them for my '71 4x4 when I changed from 4 speed sm465 to 350TH. Getting older with bad knees and a heavy truck clutch sucks. The adapter was an "off the rack" in stock unit I was able to use without having to change any internal gearing in the trans. Went right on the side of my transfer case, connected the speedo cable to it. 15 minutes and done. Checked it with our Garmin GPS and it is dead on accurate. Think the cost was $65 plus shipping. VERY satisfied with it

[chastain90]

I checked those sites. I couldn't find anything. I sent emails to them tho. We'll see if they respond.

[jjzepplin]

Junk yard.

[chastain90]

I found some on ebay. I guess they are called speed gear ratio box.

[Ironhorse]

Apparently tciauto has changed their website since I purchased my ratio adapter. After going to their website I also could not find what I was looking for and previously purchased but hopefully your email will get some response. When I purchased my unit I drove the truck down the road, called out the truck indicated indicated speed to my BIL and he checked my Garmin GPS for the speed it was showing. Being the Garmin is satellite linked I figured it was true ground speed. Figured the speed difference from truck indicated and Garmin true speed and found I needed to speed up my speedometer by 38%. Went to their drop down section showing gear ratio units and found a 38% increase gear ratio unit. Purchased it, installed it and the truck is now dead on accurate with the Garmin. Good luck with your email. Trying a ebay purchase by guess is a crap shoot at best for getting an accurate unit.

[geezer#99]

Originally Posted by chastain90

I found some on ebay. I guess they are called speed gear ratio box.

Or ratio adaptor!
Like here.
https://transmissioncenter.net/?swoo...edometer-gears

[ochre 72]

I see you're from Georgia. I got one from Hamp's speedometer service in Roswell. He doesnt have a website. His # is 770-777-1919. He asked a few questions Tire size, gear ratio and what the speedometer read when you are actually going 60 mph. I downloaded a speedometer app.
The one he did for me was accurate to about 3 mph

[chastain90]

Thanks I'll check it out