Expert: Carl Brandt - 5/16/2004

Question
Put 33" tires on my 89 Wrangler, 4.2L, Automatic 6 months ago with no problems.  Now the transmission is throwing out oil from the front seal and the repair shop told me I would have to upgrade my differential since the tires were too big and were causing my transmission oil to boil over(he wants $1000 for this).  I have plenty of power and find this hard to believe.  He also wants to replace, at more expense, the (front tranny pump seal?) Could the tires do this?

Answer
Megan,

Yes, the tires can cause more drag on the transmission, but, this depends on how you drive it.  When you are off road, make sure that when you are in steep, or rough terrain, you run in low range, as this will not work the tranny, or the motor nearly as hard as when it is in high range.  You should add a transmission cooler to the Jeep.  These should be installed, anytime you put a heavier than normal load (such as towing or larger tires) on the Jeep.  You, probably have 3.07:1 gears in the differentials, which is, fairly high geared for 33's.  It would work much better, if you were to go to a lower gear ratio such as 4.10:1, but this is not a necessity.  I have several club members that are running the bigger tires with automatics, and the stock gearing, and they have had few problems.  The reason I suggest the 4.10:1 ratio, is that, many times you can find someone who has a 4 cyl Jeep that has changed to lower gears, making the 4.10:1 gears easier, and cheaper to get.  4.10:1 gears is the stock ratio in many of the 4 cylinder Jeeps.

My suggestion, is to find a reputable shop that specializes in 4 wheel drives, and discuss the repair work with them.  Try to locate a local 4x4 club, and talk to some of the members that own Jeeps, and see if they can steer you to a good shop.  Many times they have run into similar problems, and may even offer to help you with the repair themselves.

Carl