At least I think that's what it is.

 

I have a 2000 Forester auto with the winter package which according to what I've been able to find out means it's got a 4.444 final drive VLSD. Is this correct?

 

The particulars:

 

This Forester was diagnosed by some unknown independent mechanic as having, among other things, a "bad rear differential". When I drove the car, I did feel a vibration at speeds above 50 mph or so but to me it really felt like a U-joint. There was nothing I would describe as whining or droning. When I pulled the drive shaft out of this Forester both joints had hard spots in one direction, center joint boot was intact, but I wouldn't say the hard spots were enough to cause the vibration I was feeling/hearing, but then I'm no expert in these things. There's tons of things that can cause vibrations from CV's to wheel weights to tires etc. so who knows.

 

When I pulled the rear cover off of the diff, I saw nothing out of the ordinary, no obvious signs of bad bearings or tooth damage.

 

I have an FSM for a 2000 model year Legacy/Outback/Impreza with no mention of the Forester. The sections on rear diffs don't mention any kind of diff other then the "rear differential" so I don't know if there are any differences in the diagnostics of a Forester VLSD(?) to the open type.

 

I'll be performing the diagnostics mentioned in the manual on this diff, but can anyone tell me anything to look out for on this that might be different then the ordinary routine?

 

Thanks as always!

 

Will-

Take down the entire driveshaft and inspect it for frozen or sloppy joints,If the wear oattern is normalon the gears you are good.

 

INspect the center bearing.

 

 

Describe in great detail what your hearing and when.peed, rpm, gear, turning etc

Take down the entire driveshaft and inspect it for frozen or sloppy joints,If the wear oattern is normalon the gears you are good.

 

I've pulled the driveshaft already. Neither joint was frozen and neither was sloppy, however they both and a rough spot in one direction, but not very major.

 

INspect the center bearing.

 

The boot is intact and I couldn't detect any rotational slop, is it worth cutting the boot off and having a look?

 

 

Describe in great detail what your hearing and when.peed, rpm, gear, turning etc

 

Starting around 50 mph there is a "clunky" noise coming from the middle/rear of the car accompanied by a vibration that seems to ebb and flow as I accelerate. Gear and rpm seem irrelevant as it will happen in both third and fourth (4EAT)

 

That's about all I got from memory. This car is in pieces at the moment so there won't be any more road tests on this diff. I was told it was bad when I got the car and I'm putting a different drive train in it and putting in outback hubs on all four corners (with good bearings) so I didn't care too much to find out what it was. I only got interested once I found out in was some sort of LSD 'cause that means I might be able to sell it if it's in good shape.

 

Thanks

 

Will-

this will be a lot of work to eliminate the drive shaft as the source, but...

 

remove the rear section of the shaft, leave the front section in. and install the FWD fuse under the hood. the trans and the rear diff will still turn, but the front section of shaft w/ the support bearing will not. if it still vibrates, look elsewhere and put the shaft back in.

 

if it doesn't, then remove the fuse. if it vibrates then, you know. if it doesn't then add the rear shaft section.

Universals having a rough spot in one direction, if it was my car would be enough for me to replace the driveshaft.

Do the test listed above. Dont cut the boot to inspect the carrier bearing.

 

 

nipper

Confirm - if there's no metal in the diff and the gears look good/tight then it's not your problem. I have only heard of a tiny handful of rear diff failures on Subaru's. It's very uncommon. The VLSD components are sealed with a special fluid and in any case don't even turn when going straight so can't really be associated with your problem.

 

Are you sure it didn't have a nasty rear wheel bearing? Very common on the early Forester's and usually isn't audible till you hit freeway speeds.

 

Otherwise I would also suspect the driveline - but if you find nothing there then I would have a look at the rear knuckles as it sounds like it could be a bearing.

 

GD

Early forester rear wheel bearings werent known for thier longevity. A 2000 is old enough to be on either side of the fence, but it is a good place to look.

 

I agree the GD, rear LSD diffs rarely go bad.

 

nipper

I've pulled the driveshaft already. Neither joint was frozen and neither was sloppy, however they both and a rough spot in one direction, but not very major.

Seems to me that you should have 3 U joints?

 

 

The Viscous coupler part of the diff is completely sealed from the rest of the differential similar to the center differential of the manual transmissions. It could be possible that it is damaged inside, but highly unlikely. And you wold only notice it when turning, or if one wheel is significantly larger than the other. If the gears and bearings are good, then the diff is fine.

 

What condition are the tires in on this car? How about the axles? Any ripped boots? Any that look like they've been replaced recently?

That's what I like about this board, ya'll attack the problem like a baby shakin' dingo.

 

As I said in my last post (which I should've been more clear in my first post, my fault) I have no interest in finding the vibration. I'm with Nipper, the click in the u-joints is enough to make me replace the shaft or have the joints replaced by a shop or whatever. All four axles and all four bearing housings (and bearings) are being replaced. The tires seem to be in good shape, but we'll see if the vibration is still present when I put the car back together.

 

All I wanted to know about was troubleshooting the LSD portion of the rear diff. If everything checks out, i'll assume it's good and offer it up for sale with the option to return if I'm wrong.

 

Thanks everyone!

 

Will-

The universals can quickly turn into a big "OMFG how much damage can it do?" saftey issue. And who knows, the vibration may go away.

 

Too bad its 4.44. If it were a 3.90 I'd be interested.