Five problems related to differential unit have been reported for the 1999 Toyota 4Runner. The most recently reported issues are listed below.
My truck was being driven on a long trip. The differential starting making a whining noise that got louder and louder. I stopped at an oil change place at my destination to have them check the fluid. It was almost empty. Topped it up and chanced driving it 400 miles back to chicago. I made it ok and had mechanic look at it. The differencial was so rusted that it had holes that allowed it to leak. The mechanic tried to find a used one but they all had the same problem. An internet search turned up countless examples of rusted differentials on Toyota trucks spanning many years. There is also extensive rusting on the frame, axle spare tire mount. This is obviously a long term Toyota problem.
The contact owns a 1999 Toyota 4runner. The contact noticed that his differential housing was leaking fluid. The vehicle was taken to the dealer; however, they did not offer any assistance. The manufacturer was aware of the failure. The vehicle was not repaired. The current and failure mileages were 135,000.
There is significant rust on the frame of the vehicle. Particularly where the control arms are welded to the body. In addition, the rear differential has completely rusted through and has resulted in gear oil leaking through multiple holes in the differential cover. The entire rear end will need to be replaced in order to remedy the issue.
1999 Toyota 4runner rear differential housing rusted through.
Several suspension and structural components of my 1999 4runner are showing excessive rust. The worst of which is on the rear axle and differential housing. I've recently had to weld a broken stabilizer bracket. The differential housing has rusted so bad that a hole has formed and gear oil is leaking.