Frank-D
The axle ratio is sometimes on a tag attached to the rear axle cover.
There were three ratios that I know of in the "X" line, 3.50, 3.73 and 4.10. Some but not all, came with posi units.
Now, think about what you want to do with your "X" before you change the tire/gear ratios. The gears should be directly related to the tire outside diameter and your use.
If you want Autobahn speed type gearing then you want something lower numerically, if you want trail gearing then you want something higher numerically.
When you find out your existing gear ratio/tire OD then you can determine the necessary changes.
Here is how:
New tire OD divided by new tire OD equals gear ratio change (even if negative), this ratio will determine where you go with your gearing to achieve the same performance that you had as stock or at least before you changed your gearing/tire size.
Take that ratio and multiply the gear ratio that is in your vehicle now, this will give you the new gear ratio that is required.
Let's see: new tire OD = 33" divided by old tire OD = 30"; this equals a required gear ratio change of 1.1 in order to keep the same performance. Multiply the old gear ratio of 4.10 (let pretend) by the gear change of 1.1 and you get the new gear ratio of - (drum roll)
"4.51" - 4.51, I have never heard of the ratio 4.51, well you are right go to "4.56". Most companies make 4.56 gear sets.
So you see changing the ratio is a direct relation to the tire diameter you WANT to run. Make sure of the new tire diameter before doing the gear change and you will be happier in the long run.
To answer your question - there are a lot of places to get gearing; one place that comes to mind is a company called "Superior Gear". They have everything you will need for the swap. Always use a complete rebuild kit when installing the gears, i.e. new bearing, seals and gaskets. Also, when and if you decide to do the job - keep all of your shims separate. There will be shims on both sides of the carrier and for the pinion. Keep each set separate and mark them where they go when you take them out. Clean them up and measure them; this measurement will give you two things. 1) A good starting measurement for the new shim packs. 2) Sometimes you can use the old shims as is, that is if they are in good condition not burnt or dinged up too bad, they will go back in and the gear set will position right where you need it.
Good Luck on the project, it is not an inexpensive project because you need to do both the front and the rear in a 4x4 and my thought is that it should not be done by an inexperienced person without supervision.
Sometime is pays to pay for the job done right.
everywhere but I don`t find something. But my X was stock until I began with the modifications, so I think it would be the stock ratio. 2. I`m now running 31" tires but when they`re gone I would put some 33" on my X! 3. I had to order the parts in the USA by my own cause in Germany it`s very hard to get performance parts for Xplorers! 4. What about the tachometer? Must I calibrate it after changing my ratio?5. 3 of my friends are car mechanics so that would`nt be so hard-i hope!
Hope this helps everyone 
