If it behaves as you say, it's probably a 3.90. There will probably be enough brake drag to keep one wheel from turning. As noted above you have to double the number of pinion turns to get the ratio because the differential gears have a mathematical doubling function if you hold one side.


1951 3800 1-ton
"Earning its keep from the get-go"
In the DITY Gallery
1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.