I recently drained and refilled my rear diff in my 2002 3rd gen. I do not have the greatest area to work from, so when refilling the rear diff, the vehicle was facing uphill (the rear diff was downhill). I filled it up until gear oil started flowing out of the fill hole, but squeeze a bit more in since it was facing downhill. I took out my 4runner this past weekend for the first time and put around 200 miles on it. Everything seemed fine and running smoothly.

However, a few days after it's been parked, I noticed gear oil leaking from the driver's side rear tire.

My question is, are the rear seals leaking because of a possible over-fill of the rear diff, or does my rear diff fluid exchange have nothing to do with it?

If it's just because I over-filled the rear diff, then parking on level ground and removing some of the fluid should solve my issue. Unless I've caused more damage to the seals with the leaked fluid. It's hardly any amount of fluid as you can see in the picture.

If this is just a coincidence, and my seals just happen to go bad and started leaking, then I need to look into replacing the rear seals and bearings, which I am hoping is not the case.

Let me know everyone's thoughts.

EDIT: I warmed up the vehicle and parked in on level ground. When I pulled the fill plug, no fluid came out. I filled up the rear diff fill until fluid was barely, just barely dripping out. I cleaned up the area around the rear seal on the tire, and will sell if any more leaking happens.

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By chance were you able to tell if it was low when you first drained it? I'm not 100% sure on the rear axle seals, but I wonder if it's possible that when it's full it leaks but then it leaks down to a certain point and then stops.

When you opened up the axle did she hiss at all? (As in, was the rear axle under pressure)

I am pretty certain it was not low when draining it. I just drained out all the fluid, at least 2.5-3 quarts. Which is what my Rear diff 4WD w/ locker FSM states for capacity (2.9 quarts).

The axel DID NOT hiss when I opened up the rear diff fill or drain plug. So rear diff was not under any pressure.

It shouldn't build up much pressure with a plugged breather, simply because the axle seals won't hold much, the air will push on out through them, and take some oil with it.

I'd first check the condition of the breather - it's on the top of the pumpkin, on the left side of it. It's a little 'jiggle valve'. Quickest check is to just see if the metal cap on top of it can jiggle around. If so, it's probably not stuck? But it might be worth the effort to take it off and check.

If that is NOT stuck, then you are going to need to replace the axle seals, and almost certainly replace the brake shoes as well. Soaking them in oil is not good. Possibly the rear bearings as well. But unlike some vehicles, these are sealed, so it's not as easy for an oil leak to wash out the grease and ruin them. But if you're up there in miles (like... 200k+) it might be a good idea to go ahead and replace them jsut for peace of mind?

I have never seen a leak like that, it's almost like the seal is gone. Usually a little bit seeps out and gets flung around the outside of the wheel, in a radiating pattern. Your pic looks like an actual leak.

Are you sure it's gear oil?
Checked your MC level lately?

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I am not 100% sure it's gear oil (I was making an assumption based on visual evidence). It's not sprayed radially like other leaking seals, so I'm wondering if it started leaking after driving and parking it. I only drive it on the weekends, sometimes every-other-weekend.

I checked the master cylinder and it's full. I recently bleed the brakes and cleared out the old fluid and replaced it with new fluid. It's plenty full.

The breather is able to move and is NOT stuck. I didn't take it off, just moved it around with my hand, and it's freely spins and moves.

This "leaking" issue has made me start to think about the possibility of getting new seals, bearings, and drum brakes. Not sure when the last time it was done (only had the vehicle for 20K miles). I may just monitor it , and if it's still shows signs of leaking, I'll replace it all.

Gear oil has a very specific smell……


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And viscosity

Looks exactly like when my axle was leaking, except mine was passenger side.

Looks like an axle seal leak to me. Put the rear axle on jack stands, remove the wheel speed sensor, and spin the wheel/axle shaft while looking at the tone ring through the wheel speed sensor hole. If it’s wet then your rear axle seal is leaking beyond any doubt.

The cap of the breather will move freely. The mating surface may have the flapper suck closed. The setup in the breather is the main body, flapper, spring and then the cap. You can pry open the cap (watch for the spring), clean the flapper and reinstall the cap.

Shit, you just reminded me that I need to change my drums...

But anyway yeah I've been thinking about the rear seals and bearings as well. It seems like a fairly easy job except I am not good at bleeding brakes... So that part I'm not so sure about.

so you think changing bearings and seals seem simple but bleeding brakes is not....am i missing something here

Let's just say the last time I tried it there were scary stopping issues... Lol.

Plus, are you supposed to use that pressure machine? I can't quite remember as it has been too long.