Diff Damage Diagnosis

[squidflakes]

Hello,

I just bought a 2005 Legacy Wagon and had the rear differential blow out while on the freeway. 

 

Like, really blow out. 

 

Replacing it looks pretty straight forward but I had a couple of questions about diagnosing the cause after the fact and what, if anything, should be replaced. 

 

So first off, has anyone ever had a similar issue? Due to the way the housing cracked I'm guessing that the oil in the diff had never been changed and however many thousands of miles of thermal expansion and wear caused fatigue, which resulted in the gears coming unmeshed, banging around the inside of the housing, and peeling it like a banana. 

 

Second, if the CV axels teeth are still ok, can they be reused or should I just plan on replacing them? 

 

Third, is there anything to check in the transmission that might have been damaged? 

 

Finally, it looks like the CV axels are reasonably easy to get out, but how do you get them back in? Is there a tool for this or is it just tappa tappa tappa until its seated? 

 

[m sprank]

You good sir know how to properly brake sh^t.  I commend you on the thorough destruction of that rear diff.

Make sure the replacement is proper to mate to your transmission.  Now crack that biatch open cause that is NOT normal, but could be fascinating. 

The transmission could have been damaged, but cheaper to replace diff and find out over cracking that open too. If you are going to keep the car even if it means a complete driveline replacement of course. 

[silverton]

I've never seen this kind of damage to a subaru rear differential.  They're used so lightly they SHOULD outlive the car by at least 100k miles.

You're probably correct in your prognosis, I'm sure 20 year old, and how every many million miles from factory, gear oil will eventually make it fail in this way.  Judging by the general 'gooeyness' of what's on the exterior of the case, that's no longer oil, it's molasses.

[squidflakes]

Ok, so it took an absurd amount of time to get the crossmember bolts out and finally drop out the rear diff but its out, apart, and entirely not what I was expecting. 

I found three bolts that had come out of the ring gear carrier, one was sitting right in the center of the diff getting chewed on by the gears while the other two were in the bottom of the housing up near the pinion gear. The teeth on all the gears are in surprisingly good shape considering they were mashing on some bolts for a while. The diff gear holder has some superficial damage but the gears still mostly turn. There is still a point where they will all bind and stop and I can't force them to move again by hand. If I push them in the opposite rotation they are fine for as many turns as I want. 

One thing I can't figure out, in the last picture are all of the little teeth that fell out when I opened the diff carrier. I didn't see anywhere that looked like they'd broken off, but I also didn't pull out the main shaft or the pinion gear. It is entirely possible that one or more of those things coming off and rattling between the ring gear carrier bolts and the housing caused the bolts to loosen, then fly around and cause the rest of the damage. 

 

Now the real fun begins. I need to find a replacement and the 2005 Legacy doesn't seem to populate our local junk yards. I'm guessing that any year Gen4 Legacy with the 4.11 final drive will work, as will the Outbacks as long as I keep the axels. Can anyone confirm or deny here? 

 

 

 

[KZJonny]

Those loook more like bearing rollers than broken off teeth to me? Maybe the pinion bearing came apart?

 

Outback doesn't have the same gear ratios as Legacy, but I forget all the differences between years and models and the like. The info is out there.

Like here:

https://www.cars101.com/subaru/legacy/legacy2007.html#options

[KZJonny]

Vs. Outback:

https://www.cars101.com/subaru/outback/outback2007.html

I realize I grabbed the '07 as well, but you can navigate around, clearly. I think there was a ratio change between pre and post facelift, but I also don't think the FD of the system was changed. So only an Outback 5MT would work for you.

 

This is a Legacy GT or 2.5i wagon?

[squidflakes]

Its the 2.5i with the 4EAT 

[KZJonny]

Okay. I've got a diff hanging around from a 5EAT, but the final drive isn't going to match. I'd have sent it off for the cost of shipping.

 

On the plus side, there were probably more 4EAT 2.5is built than any other model across the board, so they should be the most common differential around.

 

Tried car-parts for one?

[squidflakes]

Man, I can not tell you how much I appreciate the offer. 

 

I did check car-part and got... nuttin. I went ahead and sent an e-mail so hopefully someone can source it. I'm reaching out to yards in other cities too, so we'll see what happens. 

Worse comes to absolute worst I've had a couple of hits on Ebay, but they look dicey and have hundreds of dollars in shipping fees. 

[Infosecdad]

Where are you located? 

I have a 4.111 rear diff, just not sure it's cost-feasible to ship it to you depending on how far you are from TN.

[squidflakes]

5 hours ago, Infosecdad said:

Where are you located? 

I have a 4.111 rear diff, just not sure it's cost-feasible to ship it to you depending on how far you are from TN.

I'm in Houston, Texas. I've found a couple candidates today but one is in Illinois and the other is in Oregon, and shipping on either is getting quoted at over $200 on top of what they want for the diff.  

[KZJonny]

Go with @Infosecdad's part!

Failing that, if you think the teeth on the diff are salvageable. I could always just gut the one I have and send the case?

Better option is a whole unit. Plus, if it came off of a GT, you'll now have limited slip in the rear, which is a bonus. Pretty sure the 2.5i does not have the VLSD in the rear. At least mine doesn't seem to, I can get a three wheel peel easily enough on bad roads with it.

[squidflakes]

On 6/3/2024 at 12:06 PM, KZJonny said:

Go with @Infosecdad's part!

Failing that, if you think the teeth on the diff are salvageable.

 

The teeth seem to be in ok shape and I can spin the diff by hand in one direction, but if I spin the other it goes about a turn and then stops. I don't have a lot of experience with transmissions or gear assemblies so I don't know if that is expected or if that means something is lodged somewhere I can't see it. 

 

I'd definitely rather have a whole unit as I need to get this thing drivable and reliable enough for my kid to take back to school. Though, I'm also really tempted to just give her my Toyota and turn the Legacy in to a budget sleeper...