do i need to re gear

just bought a 91 mj 2wd with a 5 speed trans and now im looking for a donor xj the mj has 3.07 in the rear and im wondering if i will have to regear if i put a dana 30 up front im planning on 4 to 6 of inches of lift with 31 or 32 inch tires this truck will be a dd and planning wheelin some any help would be appreciated

i am on 33's w/o regearing and i am living w/ it but i am going to regear as soon as possible. i believe the biggest discrepensies you want between the front and read is 1%. it kills your milage and you can't climb hills if you actually want to wheel in rocks i would reccomend regearing so you can get some rpm's especially f you want to go larger. i have about the same lift on 33's and iyou can fit w/o a lot of trimming

most of my wheelin will be trails and a little mud no rock climbing

4in lift and 31's...no. any bigger and it will just make everything easier including your daily driving. w/o your engine has to work very hard in low rpm's. your motor will be happier at higher rpm's all around. i have been driving mine not regeared and 9mpg sucks. soon to change hopefully. check crash's sticky at the beggining of the forum

yeah 9mpg would suck im getting 22 now i know that lift and tire will make it go down but i cant dd at 9mpg

If you get the D30 from an XJ with a 5 speed which is what I assume your doing it would also have 3.07's obviously, if its an auto with will most likely have 3.55's if its a newer one, can't run that with a front driveshaft

My 94 4.0 had a 5 speed, stock gears, and 31's... I had to work the transmission to keep power on upgrades on the highway and hills, a downshift to 3rd if I really wanted to keep my speed, but I didn't get that crappy of mileage. If I remember I would get like 17 maybe 18 around town but I was easy on it. I also wheeled it for about a year, it was ok. Is the MJ a 4.0? must be with the 3.07 gears.

my 97 with an Auto has 30's on it and even that sucks, it gets like 13/14 around town and maybe 16 on the highway if its not flat, I really wanted to regear but its $$$, I can't justify putting that amount of money into it.

Its not something you have to do if you match up the ratio's on the axles, it would def help but if you stay with 31's it won't be horrid judging from my experience

yeah it has 4.0 in it

if u cant find a complete donor and u do get parts out of a junkyard, get the axles from an auto with 3.55s, ive heard that with a 5 speed 31s and 355s that its a great match, thats what im doing with my mj, ive already have a d44 from an xj now i just have to gather the energy to pull a non disco 30 with 760 u joints, good luck

the 3.55s sound good will i have to install a sye with that much lift

mjs dont usually need it cuz of the longer wheel base

thats good news im on a tight budget thanks