My first question, where is the gear ratio tag supposed to be located. No luck finding mine. Second, what gear ratio am I likely to have in a 99 XJ 4.0L with Command Trac?

 

I don't remember where it should be located, but you should have 3.55's since you have an automatic.

 

thanks for the info....now to find a dana 30 with 3.55 gear ratio

 

I would not guess at what ratio your gears are, sometimes when people service the rear end they dont put the tag back on. Some of the automatic had a 370 ratio, but the best way to find out is take the cover off of the rear end and count the the teeth on the ring gear and the pinion gear, divide the pinion into the ring gear and you have your gear ratio. T make sure count the teeth a couple of times, and sometimes the ring gear, "that being the bigger gear," has the ratio stamped on it, turn the ring gear and look for some stampings on the ring gear.
Hope this helps.
From and old gear who used to rebuild these rear ends, " I always considered myself a rear end guy," lol.

 

the tooth count will be stamped along the edge of the big ring gear. last set of digits. divide those for gear ratio.

example...

45 divided by 11 = 4.09 (aka 4.10:1)


but you most likely have 3.55 gears

 

much appreciated. My front end diff is making noise, so I am looking for a JY replacement with the right ratio. I guess I will go ahead and take that apart today and count some teeth.