Question? Trying to figure out if my gears are same in front and rear , Would it hurt if I lifted Jeep in the air and put in 4wd so all four tires would spin? Or would it bind and break if there not same ratio?
Charles, welcome, but this is a 2 year old post.
To answer your question, if the front gear ratio does not match the rear, serious driveline damage would occur if you could even move it at all.
It won’t hurt anything to jack up all 4 wheels and idle the vehicle in gear, but it won’t tell you anything either. Instead of starting the vehicle, put it in neutral, mark the top of the tire, front or rear, turn the front or rear driveshaft 3 times. Do both and compare how far each turns. They should be the same. If they are not, do not use 4wd 'cause someone changed on or the other axle. That method eliminates any over-running clutches or differentials that might be in the transfer case.
If you do this up in the air, no damage will occur. But the front and rear differentials have to have the same gear ratios and tires with the same outside diameter if the vehicle is on hard pavement.
Some vehicles cannot be put into 4wd on hard pavement or the transfer case will bind up. They can only be put into 4wd where the tires do not have good traction, like sand, loose dirt, mud or ice/snow.
A lot of modern transfer cases have something inside that allows some slippage to occur. If not they would bind in 4wd on dry pavement when ever the steering wheel was turned because the front tires take a different track than the rear tires.
Why do you ask?