I change my car`s viscous coupling and share with you
its very handling now, its very important part.
Car always oversteer when turn fast cornering before, now its like a train

You need drive car an half hour before the test. Vc must be come to operating temperature.
(thanks to @nick and @Barış from subaruimpreza.org forum)




Jack test:
wheels must be turn same speed when after car is moving
[ame]www.youtube.com/watch?v=Qt3jJAPvJ-0[/ame]

Before
you can see, rear wheels turn many time
and after the car move rear wheels turn faster than front.
[ame="http://www.youtube.com/watch?v=Dwsz9dLYutk"]Alfa 155 Q4 old viscous - YouTube[/ame]


After
rear turn just quarter before moving
then turn same speed front
[ame="http://www.youtube.com/watch?v=EvAYR8nE4TY"]Alfa 155 Q4 new viscous - YouTube[/ame]



This is handy check:
lift car, gear is neutral position and handbrake on (lock rear wheels)

Before
[ame="http://www.youtube.com/watch?v=vlqyVUpIO9k"]Alfa 155 Q4 old viscous - YouTube[/ame]

After
[ame="http://www.youtube.com/watch?v=_poBMRqSCec"]Alfa 155 Q4 new viscous - YouTube[/ame]


some pictures about viscous coupling: