viscous coupling

donald girod · 2005-05-23T00:57:13+00:00

I have a 2001 Impreza standard trans., and I understand that the rear wheels are driven thru a "viscous coupling". I would like to know just how this works. What I have read indicates that the coupling contains two sets of interleaved disks, one set driven by the transmission and the other set connected to the rear drive shaft, hence driving the rear wheels; the coupling is filled with a heavy silicone fluid which transmits torque from the transmission to the rear axle when the relative rotation between the sets of disks exceeds a certain rpm.When you are driving in a straight line on dry pavement, is there in fact any torque transmitted to the rear wheels? That is, is the normal relative rotation between the disks significantly greater than zero?At what relative rotation rate does the transferred torque become noticeable? Something I read indicated that at a relative rpm of 100, the transferred torque is about 70 ft-lb.Obviously if the front wheels lose traction and spin, torque will transfer to the rear. The reverse situation seems to be impossible, since at least one front wheel would seem to have to be rotating faster than the rear ones in order for any transfer to take place. Although in a turn, the rear wheels turn faster than the front wheels and I guess would feel some drag. Do I have this right?

May 23, 2005 41 Replies

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transfixed 21 years ago

You are right. I got things mixed up. Sorry - I didn't read the first post right and it went downhill from there.

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Edward Hayes 21 years ago

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