Center Differential Testing for damage?

[MikeC5]

I've been reading through the many posts on the subject of tire circumfence differences and the possible ill effects on the center diff. I have a 95 Legacy MT which has 140K miles from the previous owner. I would like to know if there is a relatively simple way to test the center diff. I understand that if it gets abused, at some point the viscous goo breaks down and is not able to transmit torque to the rear wheels. Is this correct?

[MikeC5]

I've done a lot of searching on this subject and am suprised to learn that very little information is published on these center diffs at all. Is there anyplace other than Subaru who sells replacements? I found a site on the VW Vanagon AWD system which uses a viscous coupling (but also has a manual locking ability). They quote a 6% rotational speed difference between front and rear driveshaft before the visco goo begins to heat up and transmit power. I was able to do a very unscientific test of my AWD system this weekend though; in packed down snow, I mashed it in 1st gear and observers (not in the car) said both front and rear wheels appeared to be spinning at the same rate....

[Legacy777]

No, you really need to get the viscous coupling from subaru.

[BAC5.2]

For a viscous unit, stock is the only good way to go. There are aftermarket solutions, but no viscous units that I know of.

As for knowing if it's blown? I wouldn't worry about it. I'd be surprised if a 95 MT wagon would be able to put the stress necessary to break down the viscous "juice". I'd imagine you'd be fine.

If you notice that you can break the front wheels loose very easily, then you might have reason to believe that something is wrong.

[bmxkelowna]

If you notice that you can break the front wheels loose very easily, then you might have reason to believe that something is wrong.

this is the problem i am having with my 92 ss
the fronts seem to spin really easy in snow or in rain and it does not feal like the back is doing much of any thing

[MikeC5]

True, the wagon doesn't have a lot of power. I was more worried about the previous owner doing something stupid like different sized tires, running with the spare too long, etc. The 4 wheel spin test on a slippery surface is at least some piece of mind that things are working as they should.