I got my Jeep a month and a half ago and immediately fell in love with it. I plan on doing a lot of things with it, but before I do, I have a question.

I'd like to do a 2.5" lift and get larger tires. Right now, the Jeep ('96 Grand Cherokee Limited) is bone stock with the exception of a Pioneer radio and Pioneer speakers in the doors. I've done all of the run-of-the-mill things like changing all the fluids, replacing belts and hoses, distributor cap/rotor/spark plugs, etc. Now I'm ready for modifications, but my friend keeps telling me that if I do the lift and get larger tires, I'll have to change my differential and tweak my transmission.

Do I really have to do all of that stuff for a 2.5" lift and larger tires?

 

Depending on the tire size you may want to re-gear the diffs. But this is not necessary, many people do just fine with larger tires and stock gearing. You will want to make sure your axles are centered after your lift. Since you are coil sprung front and rear you have a track bar both front and rear. Some drill a new hole (there is a write-up somewhere) to relocate stock TB's. Or you can purchase new/used adjustable TB's

 

Thanks!

As for tire size, I plan on 31", and re-gearing the differentials shouldn't be a problem. Centering the axles is also something that I should be able to do, so that's good news. I was really worried that I would have to tweak the transmission, which is something that I don't know how to do.

The reason why tweaking the transmission for new tires raises such a concern is because I had a transmission explode on me a couple of vehicles back (Dodge Dakota Sport) when I put extremely large wheels on it (22" rims (I was young, stupid, and didn't know any better)). The transmission, apparently, could not handle the wheels on the 16 hour drive from Iowa to South Carolina.

I'll be getting new wheels and tires for the Jeep this coming weekend, and the lift kit should arrive by then as well. I'll change the differentials as needed.

How do I tell if the differentials need to be adjusted?

 

You should not be worried about a stock transmission and tcase for a jeep if going up in tire size unless you start to get stupid - 40" etc. Up to 35's you'll be fine, it's your diffs that will need the attention.

The only concern with bigger tires for most transmissions is the addition of extra rolling mass.

You can over come this a few ways
-install a tranny cooler - this will help things from heating up on long drives and towing so the transmission won't burn up.
-Don't drive in OD when in hilly terrain or when hauling a heavy load - this will keep your whole transmission happier- locked up fully and not lugging and wandering between gears. You will lose a bit of MPG.
-change your tcase and tranny fluid more often and look for HD lubricants to deal with increased pressure and demands. Look for red fluid, not brown or burnt smelling.

 

^x2

buy a trans cooler great for anyone with bigger tires.

I wouldn't worry about regearing until you go to 33's or bigger. 31-32's are managable with stock gearing, regearing for tires < 33's isn't worth the $ IMO.