Just found some really interesting information about why a vehicle with a LSD might seem to have a slipping clutch but doesn't.
Here is a bit of the information:
"EXEDY Tech Information
Application: Subaru Impreza WRX & Sti
Subject: Clutch Slipping, but it might not be a Clutch!
If you have a concern about the vehicle's clutch slips under hard
acceleration but drives normally or better under light acceleration,
it might not be a clutch.
Before you start to change or complain about the clutch, you may
want to check if the retaining clip on the inner end of rear axle shaft
has come off or not.
Why check this part?
If the clip has come off, the axle shaft can move outward slightly to
disengage from the side gear of the rear differential but, the wheel
bearing retainer assembly will not allow the axle to come out
Since WRX has a limited slip rear differential, there is enough drag
torque to move the vehicle under light acceleration but not under
How to determine
Put the vehicle on the lift. (such as 2-post lift: all wheels must be
Start the engine and put in gear. Engage the clutch and see if all
four wheels are turning. If there are any wheels not turning, inspect
the wheel not turning.
* Pay maximum attention for safety, such as using extra stand to
hold the vehicle stable and secure.
How to repair
Push the axle shaft inward and re-engage the retaining clip. You
may need to take out the rear differential cover to re-install the
retaining clip. We recommend to inspect the axle shaft and joint
assembly carefully for any damage.
There are several case the vehicle acts like the clutch slips, but it
is caused by above reason and/ or bad differential and/ or joint
For Technical Question;
EXEDY Clutch Europe Ltd.