Thanks Mister Two,

I'm guessing plated LSDs are 'hellical'/mechanical?

And my MY00 WRX would have a 3.9 R160 viscous rear?

I am keen on fitting a LSD rear... there is one going cheap at the moment, but I want to be sure it's what I'm after.
Apparently it's off a 97 STi RA, and was fitted to an 04 WRX.
I know the V3 RA had R180 gear, so it cant be off that (unless he changed shafts and hubs), but the V2 had a R160 plated with DCCD...

I will have to check the bolt spacing to establish if it's R160 or R180... but is there any way I can check for viscous vs plated without opening it up?

The K bit does give you the ability to distinguish R180 from a MY01 onwards STi

And to spot the difference between R160 and R180 is put them side by side, one's bigger than the other

Plated LSD is NOT the same as a Torsen Helical.
Plate LSD uses clutch plates to lock up the LSD to give a stable 50/50 torque split between the left and right axle.
A Torsen Helical uses planetary gears to transfer more torque to the wheel with the most grip. (ie. the outside wheel in a corner)

Your my00 WRX comes standard with a 3.54 Viscous LSD rear Diff

If that diff came out of a 97 RA (WRX RA - not STI RA) and was fitted to a 04 WRX, then it is a 4.44 ratio.
The V2 STI came with a 4.11 Viscous LSD. ONLY the V2 STI-RA came with a 3.9 Plate LSD

[QUOTE=Mister Two;549016]Suretrac is not a one way anything. Suretrac refers to the LSD type.

Terms like 1/1.5/2 way are used to describe plated LSDs only.[/QUOTE]

Suretrac is a torque sensing LSD, it only begins to lock when torque is applied, not when coasting, that makes it a one-way differential. And I can produce SUbaru technician literature that supports it.

Diff FS thread is here [url]http://www.perth-wrx.com/vb/showthread.php?t=40992[/url]

From his description it is a 3.9 from a STi RA, fitted by ASG to his 04 WRX.

Would this be bolt on for MY99/00?

It would be so much easier if I could find a chart of all this information, there is just so much variety and different combinations! :/

3.9 wont work in a MY99-00. These need 3.545 rear ratio. Or you could change the transfer gears from 1.1 to 1, to 1-1

[QUOTE=johnvk7;549032]Suretrac is a torque sensing LSD, it only begins to lock when torque is applied, not when coasting, that makes it a one-way differential. And I can produce SUbaru technician literature that supports it.[/QUOTE]

Suretrac LSDs dont lock with more torque input. They bias to the wheel with the most grip.

[QUOTE=Mister Two;549037]Suretrac LSDs dont lock with more torque input. They bias to the wheel with the most grip.[/QUOTE]

They only operate when torque is applied, thats what i said, to say they lock maybe is wrong, but essentially they are one way.

I've gone back over my technician reference books, Suretrac does lock, and it is mechanical, when there is a speed difference between the 2 wheels, it tries to equalize the speed, just like any other LSD.