'96 Legacy rear end fell apart. Now what?

[nelstomlinson]

I started hearing alarming clunking from underneath. Turns out the rear differential is all screwed up! The two rear axles wobble about loosely. 

Can I remove the FWD fuse and the two rear axles and drive it as a front wheel drive for a while, 'till I get it sorted out? Other than lousy traction, that should work, right?

I have two parts vehicles: a '99 Legacy outback, manual, 2.5L DOHC and an '01 Impreza automatic. Would either of those rear differentials fit, and is either one likely to have to correct gear ratio?

How do I find the gear ratio of the rear end? Is it on the door tag or stamped on the diff, or do I just have to open them up and count teeth?

[idosubaru]

make sure the diff is bad. did the axles just pop out or is the diff definitely bad?  Pop the axles back in.  

With that bad of an issue I’d wonder if the suspension is rusted and the axles have too much play or pulled out due to flex/suspension falling apart. 

what’s the last work or time this car had a tire off the ground for work?

let’s assume it is the diff:  you’ll probably just want to install the diff.  I’ve done it and it’s not hard but but it’s not as easy as you describe  

FWD will only work if it’s an automatic. Some people think manuals “have the fuse” but they don’t. Only autos. 

If auto - remove axles and beat the outer cup out of the axles to install back into the hubs to keep your wheel bearings together.  Install FWD fuse. Sounds like you’ve got parts car so you might have extra axles laying around for this purpose  

If the rear diff is bad enough you’ll have to remove that and address the rear driveshaft as well. 

You didn’t tell us enough info to tell what gear ratio you have.  99 2.5 is a 4.11. 

Is your 96 a 2.2 or 2.5?   Is it an auto or manual?

Edited December 17, 2021 by idosubaru

[nelstomlinson]

The '96 is a 2.2L automatic. The '99 is a 2.5L DOHC manual. 

I don't think I've ever changed the rear axles on this '96, though I know I've done it on one of them. This one is on its second or third pair of new rear struts. The rear suspension bushings are still in decent shape; I don't think there is a lot of slop back there.  It's probably been a couple of years since I changed out the oil in that rear differential.  Nearly as I can make out the axles are still in place, but if I wobble one up, the other goes down. That sounds like serious damage inside the gear box. 

Speaking of "remove the fuse," there is a little fuse-looking thing marked FWD at the top, back, passenger side of the engine compartment. That has always been plugged in since we bought this in '97. I unplugged that when I backed it out of the shop just now. I'm guessing that disconnects the rear drive shaft? 

I have some other things I need to get done in the shop, so I'll have to get back onto this next week. At least it moves under its own power still.

[idosubaru]

3 minutes ago, nelstomlinson said:

The '96 is a 2.2L automatic. The '99 is a 2.5L DOHC manual. 

Well good grief you're a lucky joker - those are both 4.11 final drives!  Swap away lucky duck!

You may have two issues - a failed rear diff and a bad transfer clutch pack.  But I'll get there in a moment. 

 

4 minutes ago, nelstomlinson said:

The rear suspension bushings are still in decent shape; I don't think there is a lot of slop back there.

I was thinking mainly rust like the rear cross member causing droop/sagging.  I didn't realize you were actually under there pushing things around.  I thought you just leaned over and sort of guessed what was happening. 

 

5 minutes ago, nelstomlinson said:

Speaking of "remove the fuse," there is a little fuse-looking thing marked FWD at the top, back, passenger side of the engine compartment. That has always been plugged in since we bought this in '97. I unplugged that when I backed it out of the shop just now. I'm guessing that disconnects the rear drive shaft? 

It is not supposed to have the FWD fuse in it.  With the fuse installed the FWD light illuminates on the dash and the car drives in FWD mode.  Without the fuse it runs in normal 4WD.

Technically it controls the Duty C solenoid and clutch plates - so "disconnecting the rear drive shaft" is close to what it does, but not exactly.  

If the plates are warn and sticking in the grooves - then this causes "binding".

Someone may have installed the FWD fuse to alleviate the binding.  So by taking the fuse out - you'll be returning it to normal 4WD function of a Subaru.  Keep an eye out for binding. 

If you have binding you can pull the rear housing and probably just file/sand the grooves down in the clutch basket, or swap the rear housing from another 98 or earlier Subaru (or 99 Legacy or Outback)....or reinstall the FWD fuse!

or maybe you're again lucky and the FWD fuse was installed for absolutely on reason at all....that's just kind of weird.  It would be like coming home and finding a fire truck hose connected to a hydrant and snaking across your property to your front porch....there's usually no good reason to see that. 

[nelstomlinson]

That is good news about the differentials having the same ratio!  Thanks!

[nelstomlinson]

That is very strange about the fuse. That thing I described sounds like the right one, right? I unplugged the connector from the bottom of it, couldn't see any way to lift the thing marked FWD off the top. I don't recall ever seeing an FWD light on the dash, and now that you mention it, I don't think there is one there now. Maybe that thing marked FWD is just a cover, and there is no fuse under it? I'll have to look closer tomorrow.

[idosubaru]

10 hours ago, nelstomlinson said:

That is very strange about the fuse. That thing I described sounds like the right one, right? I unplugged the connector from the bottom of it, couldn't see any way to lift the thing marked FWD off the top. I don't recall ever seeing an FWD light on the dash, and now that you mention it, I don't think there is one there now. Maybe that thing marked FWD is just a cover, and there is no fuse under it? I'll have to look closer tomorrow.

Yes it’s the FWD fuse holder. So you’re just reading the cap.  Lift that lid and install a fuse for FWD. there’s no fuse installed, just an empty fuse slot once you lift the lid. 

[nelstomlinson]

Gonna guess that any old fuse will do, there isn't enough current to notice, it's just closing a dry contact?

[idosubaru]

10 minutes ago, nelstomlinson said:

Gonna guess that any old fuse will do, there isn't enough current to notice, it's just closing a dry contact?

Exactly.!

[nelstomlinson]

I got the differential out. The passenger side bearing looks OK. The driver side bearing is a pile of shavings in the bottom of the differential case.

 

By the way, is there a way to remove a picture once it's been uploaded? Somehow I uploaded a 1meg pic that turned into almost 4megs, and it's taking up a 1/3 of my quota.

Edited December 22, 2021 by nelstomlinson
Leaving out pictures

[nelstomlinson]

It turns out that the differential is structural! I'm going to have to put it back in there in order to be able to drive. I figure I can take the outer ends of the axles off to be able to hold the wheel bearings together. The outside boots are cracking, so they were going to have to be replaced anyway.

 

I'll take the diff further apart, see if I can figure out what else went wrong, and what, if anything, is salvageable. Then it goes back in until after Breakup, when I can get at that parts car.

[nelstomlinson]

The pinion bearing looks OK. Looks as if the driver side bearing went out, wiped out its seal, let the oil out, got totally chewed up, and broke its outer race and the cap that holds the race. Unless those caps are replaceable, I think that differential is done. On the other hand, the ring and pinion gears look undamaged. That's a surprise.  Anyway, I'm going to replace the diff housing minus the ring, carrier, etc. and try to have this ready to drive out of the shop tomorrow as an FWD.

[lmdew]

Yes the stub axle has to be in and the nut torqued to keep the bearing together.

Best of luck.  Should be easy to find a rear diff.

www.car-part.com is a good source.

[nelstomlinson]

I have one that should work under the parts car, just waiting for Breakup so I can get at it. -10F and 16" of snow is NOT ideal conditions for pulling parts.

[nelstomlinson]

The old, gutted rear diff is back in place, and that was amazingly hard to do!

Is there an easy way to get it back in place and all the bolts back in? Those four that come through the front of it were about impossible to get started in the holes. The angles were all wrong. We were jacking and hammering and prying for hours.

[lmdew]

Keep everything loose until they are all started.  I've done several, they have all gone OK.

 

[nelstomlinson]

That was the problem: with everything loose, and the two studs started, we couldn't get the four front bolts started at all. The angle was wrong and we couldn't keep the threads from hanging up on the edge of the holes. That is the worst possible design!

My son is saying that next time we should yank that tunnel out, and weld some nuts on the top so we can just shove the diff into place and stick bolts up through. I think he's right - that'll be less trouble than going through this again.

Also, on a separate issue, I suspect that the subframe crossmember the back studs go into was slightly warped, because the driver side bushing got pulled WAY out toward the diff when I tried to tighten those nuts afterward. Couldn't really see anything out of straight or out of square lying underneath, of course, but something isn't right.

[1 Lucky Texan]

was the fluid OK-ish, or chocolate mousse? Sometimes, if very deep water is entered, water can get pulled in through the vent. when the diff cools from the water there is lower pressure and it can suck water in.

[nelstomlinson]

The little bit of oil that was left was black, but no sign of water. This thing has never been in more than a heavy dew since the last time I changed that oil.

[lmdew]

The four long bolts should be welded to a plate on the top.  They take a bit of messing with but should drop through the diff and plate with little problem.  Of course if things are bent, that could be the issue.

Here's a you tube showing how it should go.  Not mine but they did a pretty good job.

https://www.youtube.com/watch?v=cQpnQ7l7XLo

Hope it helps.