LSD?
 

What exacticaly does the lsd do? i got a used 4.11 rear diff. and i dont know if it has it in or reather i want to swap lsd.

Re: LSD?
 

It allows you to see sounds...

Oh crap, sorry, wrong LSD. The limited slip diff has clutches in it that force both wheels to spin together, and only allow a small relative speed difference between the 2 wheels. With an open diff, if one wheel loses traction, that wheel will start spinning. With the limited slip, both wheels would spin, so even if you don't have any traction with one wheel, you will still get some traction from the other. The easiest way to tell while the diff is out of the car is to pull the cover off and take a look. If there is a spring in the middle of the diff, it is limited slip. If there isn't, then its open.

Re: LSD?
 

If you can look strait through the Subaru rear differential, and the view is unobstructed, then look more closely with a light and see if there are two splined parts.
The drivers side always has one spline.
If the diff has three splines THEN it is a LSD.
If the view reveals an obstruction, in the form of a round rod about 1" in diameter, then this is an OPEN or NON LSD rear diff.

Re: LSD?
 

I thought our lsd's were of the viscous type?

Re: LSD?
 

They are... Easiest way to tell LSD vs Open is to turn one of the axles, if the other wheel turns in the same direction, it's LSD, if the other wheel rotates in the opposite direction, it's open. With a viscous, the other wheel may or may not turn the same direction, but if you try and turn both wheels in opposite directions, you will feel resistance with a viscous LSD, where with an open you will feel almost no resistance at all.

Older diffs will say "LSD" or "Viscous LSD" on the sticker on the rear cover, but newer ones do not have the sticker, and instead it's on the side of the diff case at the top, and it's just a number you have to look up to tell what it is.