How do I Determine the Ratio of my Ring and Pinion?
The sure way to determine the ratio of you ring and pinion is to remove the differential cover and count the teeth or find the tooth counts stamped on the ring gear. The easiest way to determine the ratios of the R&P is by looking at the tags bolted to the differential cover, or in the case of the AMC 20, by looking up the code stamped on the differential housing. When axles are built, there is normally a tag bolted to the differential cover or a code stamped on the differential housing. The tag may have the ratio specified or it may have the tooth count specified. All of the newer axles specify the ratio and some other build information on the tag. For example, you will likely find "3.07" on a Wrangler axle tag as well as other build codes.
If either the front or rear ratio can be determined, you can be pretty sure the other axle contains the same ratio. If the ratio between the front and rear is significantly different, there will be a lot of drive line binding driving in a straight line on hard surfaces in 4WD. It is not uncommon for the ratios to vary by a few 1/100s, this will not cause a problem.
You may find the tags unreadable or removed by a previous owner. In this case, the easiest thing to do is:
Raise and safely support one wheel (two if you are locked up). It is easiest to do this with the transfer case in neutral, so make sure you are on a flat surface with the wheels blocked from rolling.
Turn the wheel so the yoke aligns with a spot on the differential housing you can see from the wheel and mark the yoke
mark a point on the wheel in relation to somewhere on the body, chalk or a grease pencil will work
Turn the wheel two full revolutions and count the revolutions of the yoke.
The number of revolutions of the yoke will be the ratio. For example, if you count 3 3/4 revolutions, the ratio is probably 3.73:1.
http://http://www.jeeptech.com/AxleGeneral.htmlhttp://http://www.jeeptech.com/axle/amc20.html
