super subbie

OK, problem resolved after taking the old center diff apart. The rear drive transfer shaft, shown with the two spline sections, doesn't actually engage with the front drive beveled gear in the differential. The bevel gear, and the front drive shaft do rotate with respect to the spider gears and the rear drive beveled gear (open differential). Just not in my specimen. I needed to use vice grips to rotate the front / rear drive shafts because my viscous coupling device is nearly frozen. I heated it up a little to 120F, and it locks up completely. Put a used center diff back in the tranny, and it seems to work fine. For prosperity, here's how to check if your center diff / LSD is failing. Jack up the vehicle from the side, so that the front and rear wheels on that side are off the ground. Parking brake off, tranny in neutral. Rotate the front wheel forwards, and the rear wheel should also rotate forward. Now put it in gear and repeat. This time the front wheel forward should result in the rear wheel rotating backwards, reverse. In neutral, the center diff housing rotates freely, allowing both drive shafts to move forward together. In gear, the center diff housing is locked by the tranny and engine resistance, forcing the front and rear drive shafts to rotate in opposite directions. When I do this, it's very stiff, but the wheels rotate in opposite directions. I'm assuming under normal conditions the two drive shafts only need to move a little, and slowly, with respect to each other

Thanks for responding LTexan. I had also found those vids, but watched them all again to see if I missed something. Especially the first one. I'm going to tear my failing unit apart and see if a learn something. BTW, sliding the center diff and rear drive shaft into the transfer case, on the vehicle, is in no way as easy as that guy does it in the second vid. Took me about an hour... Just can't get around the rear drive transfer shaft locking the front and rear side gears together, inside the differential. On the bench, when I insert this shaft, the differential is locked together as if it's one big fused shaft. But there's no way that's how it was designed to work.

Yeah, I think I'm missing some something here (aka: I'm an idiot). With the rear drive transfer shaft (bottom of pic) inserted, both the rear and front drive shafts are effectively locked to each other, meaning there is no differential action at all. They are both locked to the center diff housing as well, negating the need for any kind of LSD. I'm going to replace the unit with the spare from the old tranny and put it back together. But it drives me crazy to do that not understanding how it's supposed to work. If anybody has any insights, please let me know.

Me neither. I'll try it again.

Still working on this. The tranny I removed is a TY752VAAAA. Final drive ratio of 4.11 according to the chart that is all over the net. The tranny I put in is a TY752VA2AA. It's not on the chart, but numerous sources online indicate it is also a 4.11 (Google says so, so it must be true?). By rotating front and rear wheels in various configurations, it looks like the center differential is functioning smoothly and easily. The viscous coupling device seems to be very stiff, compared to the one I have on the bench. Before I tear the center diff / VCD out, I have a question maybe you gurus can help with. Attached is a picture of my old center diff, on the bench. The rear drive shaft is connected through the drive transfer shaft, shown at the bottom. This shaft has two different spline sections, which fit into each of the beveled side gears inside the center diff. Not the spider gears, but the ones connected to the front and rear drive shaft. This locks the two gears to each other, which seems to defeat the whole function of the differential. It's like it's got a center differential, but it's locked. Any insights?

Thanks guys! Both trannys are 4.11, at least according to all the charts out there. One of the CV joints on the stubby hyper-extended itself. I popped it back in, but it wouldn't turn after install. Bought a new one, and that worked. But I think I need to have a second look at that (as soon as the temp in my garage drops below 100F..). Also, I pulled the center diff out of the old tranny. Having a hard time seeing the viscous coupling function of this thing. Looks purely mechanical. I was thinking VSC might fail intermittently with temperature. But I've been driving this thing around town for a week, trying to get it to fail again without luck. I'll report out when (if) I get it figured out.

I have a mysterious vibration problem; hoping the gurus can help. This is a 95 outback, with a 90 EJ22 in it. The tranny locked up in reverse, so I replaced it with a 93. (That might be the problem right there, but this is a FrankenSubbie for the teenagers to drive to school). The new tranny ran fine for about 20 miles. Suddenly the whole drive train seems to vibrate. Driving straight on pavement. I pull over to the shoulder, wait a while, and it's fine. This has happened repeatedly, forcing me to drive home at 5mph. I park the car overnight, and then it runs fine. The vibrations are severe. Very alarming at high speed. It feels like the whole drive train is binding or fighting against itself. And I noticed if I go over a speed bump, or otherwise unweight one of the wheels, I can hear it make a little screetch or skidding sound. I assume it's a bad center diff, but this happens when driving in a straight line. This is undoubtedly a severe mechanical interference problem, but it goes away if I park the car over night. That's the part that perplexes me. Any advise is appreciated.

Wood block and hammer would be a lot easier than disassembling the stabilizer arm / huge bolt. Should have thought of that. Discussion on the Outback only website is around how this happens in the first place. Leading theory is that the inner CV joint grease gets old, thick and viscous. When the rear tire takes a big swing, it can generate enough force to pop the spline shaft out. In my case, that CV joint was plenty loose. But this is a beater car for my kid, going to school in Durango, Colorado. Every weekend, he loads up a bunch of his buddies and they go exploring the desert or mountains. He brought it home Thanksgiving with the popped axle and a fractured front stabilizer bar. So I think if you sufficiently abuse the vehicle (and consume a sufficient quantity of beer), you can pop that axle out. Wish they would have designed it with a roll pin through the spline shaft, like on the front axles.

Thanks everybody. Figured it out from your combined suggestions. It turned out to be a rear drive axle popped loose from the differential. On visual inspection, it looks OK, so I pulled the rear differential, but nothing wrong there. Reassembled everything and it worked.... for about a half a block until the axle slid back out. The axlel is held in place with a C-clip inside the differential, so you have to make sure this is engaged when reassembling everything. I had to remove the spindle arms and give the hub a good kick. To sum it up for any other shade-tree mechanics out there. 1. If your clutch is slipping, especially as rpms increase, but you don't smell any toxic burning clutch stench, then it's probably not the clutch. 2. AWD subbies have a center differential and a viscous coupling clutch that transfers power from any spinning wheel to the other wheels. Any broken axle, CV joint or differential failure that allows a wheel to spin freely will act just like a slipping clutch. 3. The rear drive axles are held in place with C-clips on the spline shaft, inside the differential. Not sure how this would pop out, but it's difficult to see visually. Try putting the vehicle in gear, and jacking each wheel up, one at a time. If one spins freely, you have this type of failure.

NVU, thanks for the visc / diff info, I'll drive some figure 8's tomorrow, but that's not what it's doing. It flat out slips, like you can put the emergency brake on, and let out the clutch, and it will idle in 1st gear, not going anywhere. No burning clutch smell, before or after. Old clutch looked good. Also, no chatter at all, either before or after. My 95 chatters like crazy, so I know that feeling. Ido, I'm not sure there's even an English name for the clutch manufacturer. EFORTISSIMO, maybe, or that might be the distributor. So, yeah, not exactly Aisin. But I measured the new clutch thickness at 8mm. Not sure what the spec is, but the "bad" one I took out was 6mm. I was surprised it was that thick, given the sliding it was doing. A lot of accumulated oil in the bell housing, so I replaced the rear main seal and the oil separator plate with the Subaru metal replacement part. Not sure I trust that, since the gasket is just FIPG between two flat surfaces, with no channel to hold the FIPG material. Clutch, pressure plate, throw-out and pilot bearing. Cheap bastards didn't include new retaining clips, so I had to dumpster dive to find my old ones... Bought this thing for $2k back in July with 220k on it. No idea of the maintenance history, but the motor was clean and it runs well. Now wondering if the fly wheel was turned prior, but not the mounting surface for the pressure plate. Guess I'll have to tear it apart (again). Sigh.

Hey All. Installed new clutch in 1999 Outback, 2.5L, manual. Still slips, but in weird ways. Mostly in 1st and 2nd, not noticeable in 3rd or 4th. No burning clutch smell. Removed the slave cylinder from the bell housing, no change, so it's not the hydraulic system or pedal adjustment. Did not turn down the fly wheel, due to the cheap, beater character of the project. I've been reading about the viscous clutch / differential system(s) used on Subaru AWD. Hard to get a straight story. Does anyone know if failure of these components could lead to the symptoms I'm seeing? The tranny is leaking fluid toward the rear, which I think is where the center differential is located. Apparently, the VC is a sealed unit, so you can't refill it.