4Runner leaking front diff seal

Now I'd noticed a long time ago when I had the front hubs off that something was worn, somewhere between the diff centre and the wheel. Being independent front suspension, there is a Constant Velocity(CV) join between the diff axle and the stub axle. I had mentally decided firstly that the CVs were worn, then decided that something in the stub axle was worn, but I discovered it was probably all that and a bit more...

Axle removed from differential.

When a brother-in-law told me off for dripping oil on his driveway, I said "no way, the 'lux doesn't leak. When he pointed I thought "oh dear". I then stuck my finger in it and had a sniff. Gearbox/diff oil. I hate that stuff, my skin turns to dermatitis just thinking about it. Look up and sure enough, a mass of caked oil/sand/muck on the drivers side of the diff.

First up I hit it with degreaser and hosed it off. It is a good idea to find out where the leak is coming from. Once clean, it started to almost dribble out...of the side of the diff. Bugger! So I think about it - the axle that goes into the diff is bolted to a flange on the CV, you can probably replace that seal without having to even take the wheel off. I order the seal and away I go.

Differential with axle and seal removed.
Note the CV flange at the bottom.

Yep, the CV can be pushed aside so the axle can come out; but it is really close and you'll need a bit of force. There is a reverse collet type arrangement on the axle spline but two long screwdrivers either side for leverage will pop it out. It is about this time I notice there is excessive slop in the axle bearing. Uh oh.

As you can probably see on the axle photo, the axle bearing surface has spun in the bearing at some stage. Argh. The bearing is internal, that's a diff pull off and overhaul. Nup, not doing it. While we are talking about that bearing, what a strange thing it is. It looks like it has a normal inner race and outer race, but you can't "spin" it!? It seems to turn, when you twist the tailshaft, at half the speed the axle would go. What's more, looking closely, there are spiralling grooves on the axle mating surface which look a lot like oil feed channels. I'm guessing, but I'd say there once was some sort of copper/soft metal surface on the bearing so the axle actually spins in the bearing - ie, not an interference fit. I didn't care at that stage, I wasn't spending a thousand bucks on a diff overhaul so it would be knock in the new oil seal and see how it goes.

Old and new seals.

Knock in the seal, yeah, good one. Normally, a seal is only "this" big so you find a socket that is about the right size and use it as a drift to tap the seal in. I didn't have any 60mm sockets, so tapping it in became rather difficult. I fabbed ub a little wooden drift using my router, which pretty much fell to bits after a few good whacks. I then tried tapping gently around the edges to progressively seat it. Nup. After about 2 hours of futile effort, I threw my hands in the air, grabbed a file and chamfered the leading edge of the seal. 30 seconds after that it was knocked firmly into place.

New sealed tapped into place.

As they say in the classics "Assembly is the reverse procedure of Disassembly", it was back together. With the slop and play in the axle I was pretty sure the new seal was not going to last, but so far so good - no leaks after 10,000kms.

Why do I think this happened? I've got a pretty good theory in fact (aside the excessive play in the axle). When I do an oil change, the oil filter is directly above the diff, right above the axle. Being lazy, Once the sump is drained I then put the drip tray underneath the diff, take the filter off, and let the oil drain down onto the diff and then into the tray. After a while, the oil drips off but some stays behind (I don't degrease it). That oil then catches sand and muck - all of this going right up against the seal. Lesson learnt there me thinks!