Think I may have toasted the rear diff....now what?
 

So, long story short, I don't drive my 4Runner much these days, just due to work and other hobbies. But she does get driven by guests, friends, etc...

Today was the first time I've driven the truck in several months, and I immediately noticed something was wrong. I kept hearing a popping noise and at times could even feel it in the pedal. At first I thought I was just throwing mud off of the wheels, but it continued and I got suspicious. Rolled down my window so I could hear it better and heard a distinctive chirp of one of my tires stopping for a split second on the pavement....not a good sign.

So I got out and looked under and BOTH of my rear wheels were absolutely covered in gear oil. So, now fearing that I was out of diff oil, I limped it home (I was only about 1.5 miles away) and pulled the fill plug and couldn't feel any lube...damnit. Took the car, got some gear oil and long story short, I added about 1.7 quarts of gear oil to the diff.

So I've clearly got a leak that needs addressed, but what else do I need to do here? Is there some way to check for permanent damage to the rear diff from the lack of lubrication? I'd hate to do the axle seal job only to have the diff implode on me a month later. Basically, what's next? What do I need to check and in what order to make sure the damage is limited as much as possible and that my bank account stays happy?

I would pull the rear diff and look at it, it’s not hard to pull especially if you already plan to do rear axle seals, just remove both rear axles, the driveshaft, unbolt it and pull it out. If it is damaged you could probably find a used one pretty cheap if you have a common gear ratio

You should be able to tell if there is unusual wear on the gears, or you could post a pic, when I pulled mine at 190k miles the gears looked new

I do exactly what the gentleman above me said. Depending on how you drove it, there more than likely isnt any damage if it was only 1.5 miles from your house, however it sounds like it could have been driven that way before by your guests or friends, unknowing of the issue. I just posted a thread of all the OEM bearing part numbers, if you plan to rebuild if yours is shot. If you dont really mind throwing a used diff in your truck because you only drive it mildly, then thats what I would do personally. Ive dropped 4 or 5 diffs on these trucks at the junkyard and only one was bad so far.

EDIT: If you blew both axle seals, your culprit is more than likely a plugged differential breather. This would explain excessive pressure resulting in the failure of both the seals. More often than not, if just one seal goes out, it was just an old seal.

Yep, the "other people" is what I'm worried about here. Nobody in several months noticed anything wrong with the truck, but that doesn't mean it didn't exist. I noticed it before I left my driveway....How many miles has it gone without diff fluid...

Pull the drain plug and see if any chunks of metal are attached to the magnet. If it's just the usual minute metal debris accumulated on the drain plug magnet, you might be ok. The chirping of the tires isn't a great sign but it might be due to the brake shoes getting swollen from absorbing the gear oil over time and they are dragging in the drum. You obviously need to perform a rear axle seal and rear brake job. For the rear axle seal job, you should replace the bearings and other related parts. If you pull the parts off rather than cut them off the axle, you can reuse the ABS tone rings and both retainers.

This video will give you all the info you need to know about what is entailed with a rear axle seal job.

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This video showcases a better axle tool than we used in the original video and also uses some new techniques we learned doing the repair over a dozen times.

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This video will help you with the rear brake job.

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If it were mine, finding used 3rd members/rear diffs/pumpkins for these 4Runners isn't hard and not very pricey. Pick n pull yards are cheap and all you'll need to do is slide the rear axles out and undo the 12 bolts and it wiggles out. Shouldn't put you out more than $100.

This is where the 'third member' design that Toyota uses on the axles is nice. With a more conventional axle - the pinion and then the differential are bolted into the axle housing, and a lot of very precise shimming and adjusting needs to take place for them to not shred each other in short order. Not really home mechanic friendly.

But the third member contains both the pinion and differential - and removed as a set no setup is needed. Just pull the axle shafts and pop it out, and do the same on your axle. Very shade tree/home mechanic friendly.

The popping and seizing (tires skrrrching) make it sound like your diff is already junk.

I'd only bother with replacing the whole axle if you could find an e-locker axle. That is a very nice upgrade (if you wheel it).

My original goal when I bought the truck WAS to build it out, but life got in the way. I'd still like to do that some day, but finding a good E-locker diff here will probably be difficult to impossible. Is there some resource who sells known good rear diffs for our trucks? Possibly rebuilt or something? I've called a few local junkyards already and nobody so far has a rear diff for the truck, of any gear ratio...

For the longest time, all 4Runner diffs got pulled almost immediately when a truck hit the yard. E-lockers still do, but now it's 50/50 to find an open diff still in it after a week or two.

You could take a look on eBay. Not sure how much shipping would be to PR though, it's a hefty chunk of metal.

What ratio do you have?

Not sure what ratio I have. I'm also dealing with a transmission issue in our Rav-4 right now, and that one's the family hauler so I haven't really investigated my truck too much yet. Is the gear ratio printed on the jamb sticker?

I'll keep calling around locally. I've got no doubt that there is one available, but it may take awhile to track it down. Shipping to PR is pricey for sure, but it may end up being my best option / I get a known good diff for the price...

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I don't think it's always 100% accurate, but there is an axle code on the door sticker.

On most US market 4Runners you'll either see A03A (4.10) or A04A (4.30). With some other oddities for 4 cylinder, 2WD, etc versions.

*Very* generally speaking most 3rd gens were automatic. And open diff automatics usually have the 4.10 ratio, and locker diff automatics usually have 4.30.

I have a factory 5 spd manual locker, it had a 4.10 ratio.

I'm with @mtbtim on this one. Same thing happened to my '98 and it was swollen brake shoes that didn't want to release and kept grabbing and every time I stepped on the brakes once I got them to release. Even with leaky axle seals there's still a lot of gear oil in the diff. My money is on brake shoes.

I agree with tim and jmat.

Well here's hoping. Gonna try to drain the diff tomorrow and see what's up.