hi, im loking for a used jeep cherokee and i want it to de 4.10 because im gonna do offroading with it.

two questions - is there a way to know what is the ratio ??
- is 4.10 the way to go.. i want to put 33 inches tire and 4-5 inches of lift.. on it and i want it automatic...

 

I believe the 4.10 ratio was an option in some early XJs with 4 cyl engines.

 

http://jeephorizons.com/tech/xjstockspecs.html

 

Read this:
http://en.wikipedia.org/wiki/Jeep_Cherokee_(XJ)

 

Easiest way to tell the gear ratio is to look for a metal tag on the differential it should give you a number like 37/9. This would mean the axle has 4.11 gears. If that tag isn't there, lift the rear axle off of the ground and disconnect the rear drive shaft. If it's an open diff, then only have one rear tire off the ground. If it's got LSD or a locker, both tires need to be off the ground.
Open Diff: Count the number of times the yoke fully rotates while rotating the raised tire 2 times. If it has 3.55 gears, the yoke will have rotated roughly 3.5 times while the tire is rotated 2 full times. 4.10's would be just over 4 yoke rotations with 2 full tire rotations.
LSD/Locker: Count the number of times the yoke rotates with 1 full tire rotation.