I believe to check your gear ratio on an open (non posi-traction) rear differential, you jack up one rear wheel and rotate it two complete revolutions while counting drive-shaft revolutions. About 4 revolutions is probably a 4.10 and about 3.5 revolutions is probably a 3.54 etc.. On a sure grip, posi-traction, or locked type differential you raise both wheels and rotate the wheel one revolution while counting drive-shaft revolutions. That is the info I found while making my rear swap and it seemed to work well..............Tim