Viscous Coupling Test

viscous coupling locking center differential test

This video shows three BMW E30 3-series iX. The first one has a faulty viscous coupling and the center differential works as an open differential. During the jack test, the rear wheels spin freely and no torque is transferred to the front wheels. This is how any permanent four wheel drive car with an open center differential behaves.

The other two BMWs have a good viscous coupling unit and you can see that it locks and transfers torque to the front wheels.

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There are 4 comments
February 28, 2013 - 21:53

Is the viscous clutch on this system used in conjunction with a center differential, to act as a differential lock? i thought that BMW had continious RWD (mechanical engagement) and the FWD was connectet through a VC, so the torque to the front axle was limited by the VC, but the rear axle got unlimited torque.

Reply to Oskar
March 02, 2013 - 15:26

This BMW has full-time all wheel drive. Your first statement is correct.

September 05, 2010 - 22:08
Viscous Coupling Test

Would you feel a difference in the way it drove? Or, is there another way to tell if this viscous coupler was not functioning properly? I just bought my third E30 yesterday, it's my first ix. It seems to be in great condition for being a '90. No major problems, but it seems as though I need front cv boots. Is this a common problem?

Reply to Stephen
September 06, 2010 - 16:43
Re: Viscous Coupling Test

I'd expect too much wheelspin from a system with faulty viscous coupler. You can do a test like on the video to see for sure.

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