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Guest Message by DevFuse

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LSD clutch type vs viscous type?

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1 reply to this topic

#1 camosuba


    USMB is life!

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  • Brisbane Australia

Posted 06 November 2003 - 01:03 AM

Ive just recently fitted a clutch type (resonably tight clutch pack too) rear Lsd diff to my 5spd Manual AWD liberty/legacy sedan and was wondering if there are any ill effects that could be caused by this specificaly the viscous coupling in the rear of the transmission? I understand the theory of the clutch type workings but i need some enlightening with regards to how a viscous lsd works does anyone have a schematic of one ?

#2 Commuter


    Subaru Master

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  • Niagara area, Ont Canada

Posted 06 November 2003 - 05:11 PM

I don't have time to dig it up right now, but I think the "How stuff works" site has some info on viscous couplings.

They are a sealed unit with thin closely spaced (not touching) discs that have holes and slots in them. The odd numbered disks are attached to one shaft, the even number discs to the other shaft. The whole unit is filled with a silicone oil.

Silicone oil (fluid) thickens dramatically when it heats up. There is a huge swing in the viscosity around 100C. If both wheels are turning at the same speed, the discs are as well, there is no relative movement between the disks and the fluid is at it's low viscosity, allowing slight movement for turns, etc. When one wheel spins, there is relative movement between the discs, the fluid is sheared, it heats up, thickens and "locks" the plates together, thereby transferring torque to the wheel with grip. This happens very rapidly, but not instantaneously.

The center differential in most manual transmission Subaru's use a VC to power the drive shaft to the rear wheels. (Auto's have the clutch pack.)


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