Hello fellow 4Runners!

I desperately need some of your thoughts regarding the following mystery!

I own a 1998 4Runner limited. It currently has 350000kms. I bought the unit back in 2000 at which time it had around 150000 km's on it.

Right from when I bought it, the rear axel seals were a problem - about every 1-2000 km's they would begin to leak which usually meant replacing the shoes as well ...$$$!! I searched for months trying to figure out why the seals would not last. I had two very good mechanics work on the mystery (one of which was a certified Toyota mechanic) and after doing about 6 seal jobs on the unit, we finally concluded that the rear diff. must be bent due to some sort of previous impact.

I finally replaced the whole rear diff. with a diff out of a 2000 4runner. That was about 60 000km's ago. Everything was fine up until about two months ago - then the mystery returned!!!! The rear axel seals are now lasting about 1000kms WHAT IN THE HECK IS GOING ON!!!!!

Basic things have been checked, such as the rear diff vent, and the work has been done by the good certified mechanic - he is now as dumbfounded as I am!!!

Ive come to the conclusion that some sort of external factor that has been a constant influence on both the old diff. and now the new one, MUST be involved in causing the seals to lose their ability to seal properly for any length of time.

Here are my guesses:

1) Could agressive 10ply hard off-road style tires used for highway application be causing too much vibration for the seals to handle? I've always had these types of tires on the 4runner because I do go off road sometimes (although the off-road conditions I encounter are very tame [not mud-bogging or anything like that] - the rest of my driving is all hwy use.

2) Could there be a problem with the rear diff. fluid? Would it possibly be an option to go to a thicker fluid?

Any ideas or guesses or ideas would be GREATLY appereciated! I love my 4runner, but I'm about ready to drive it off a cliff somewhere!!!!!!!!

 

If youve looked over everything else and all seems fine, i would swap the heavy 10 plys off there and put on some regular pass tires. I had some 6 ply (IIRC) that were on my 2000 4runner when i had bought it and although nothing bad happened to my truck, those damn tires are waaaay to heavy to be rolling on Toyotas drivetrain (IMO). I dismounted them and they were the heaviest tire i have seen on a pass vehicle. I can only imagine how much yours way??!! It seems to me that the extra rotating mass and or poss vibration of those heavy ply tires are either stressing the axle causing it to flex or just beating up the bearings and seals. Anytime you have to replace seals back to back like that, your better off changing out the bearings the next time too as the seals will not make up for a played out bearing.
Good luck