New clutch, still slips

[super subbie]

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. 

 

[nvu]

Guessing it was making burning smells before?  If it did and only the disc was replaced, chances are the flywheel and clutch cover are uneven.  You might be experiencing clutch chatter.  Maybe it's uneven clutch material from the prev clutch, and would go away over time. 

The viscous coupling portion could be completely failed and you'd never notice it in straight line.  It doesn't cause the issues you're seeing even if failed and you can still drive it.  Center diff/visc coupling can be checked by driving in figure 8's, a worn one will feel like it grabs with tension then lets go over and over.  If the center diff portion starts failing, you'll hear an awful noise and likely lock all 4 wheels when it completely fails.

My 98 outback sport has chatter only when inching along in stop and go freeway traffic and things heat up.  To get going from a stop, I blip the pedal to 2k and release the clutch as the rpms falls, gets it going with no chatter.  Press the throttle again once the car starts moving.  It's a smaller car with a cable clutch so it's all or nothing when it comes to grab point range.

[idosubaru]

it's not diff or VLSD related. 

1. what brand clutch - i don't think it would be even a small surprise for a cheap clutch kit to have issues out of the box?

2. was it wet inside from any fluid leaks?

3. what was replaced - *just the clutch*...pressure plate, throw out bearing...?

 

 

[super subbie]

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.

 

[lmdew]

When you put the break on and let the clutch out in 1st, have you looked at the half shaft inner joints?

If one if failed it would just be spinning away.

[Numbchux]

I've known people to misdiagnose a CV axle as clutch failure (as the VLSDs transfer some power to the other wheels).

[lmdew]

I've had a few rear axles pop a 1/4" out of the rear diff.  Feels like the clutch is slipping.

With no movement in 1st with the clutch out and brake on, I'd think it would have to be the front CV.

[super subbie]

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. 

[forester2002s]

Thanks for the update.

[lmdew]

It had it on a couple of different Subarus.  Unless you know you will most likely not find it.

[idosubaru]

On 12/18/2019 at 7:00 PM, lmdew said:

I've had a few rear axles pop a 1/4" out of the rear diff.  Feels like the clutch is slipping.

With no movement in 1st with the clutch out and brake on, I'd think it would have to be the front CV.

Nice work!!!  Have you had it happen on manuals only or autos as well?

[lmdew]

All of them were manual trans, for me anyway.

[Numbchux]

I saw that once, as well, but it had had the rear diff out of it recently, and the guy didn't know to engage them all the way. Haven't seen it on a car that hadn't it been removed.

 

With a wood block on the edge of the cup, you can put enough of a whack on it to engage it into the diff without damaging the boot.

[super subbie]

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. 

[Rampage]

Sounds feasible, it's the beers fault. It can mess up a lot of things.