How quickly should the AWD rear kick in?

[Gene J]

My 98 GT wagon has a manual transmission. How quickly does the center transfer actually operate since it is a fluid coupling and has no clutches?

 

To test it, I put the front wheels on a patch of ice and the rear wheels on dry pavement. The front wheels did spin. But the car did move forwards. Just not as quickly as if it were a RWD car and fully engaged.

 

Did it work properly? Is there some other way to test the AWD?

[Suzam]

All the Subies I've had are automatics. If I put the fronts on ice I'll get a little slippage then it goes. Almost not noticeable.

 

I know the auto is 90/10 but with 50/50 of the manual I would think you could expect less front slippage?

 

Which raises a good question:

 

Does the Viscous coupler on the manual trannys delay engagement of the rear wheels more than the auto Duty C clutch packs?

[ericem]

I think it would be delayed if the transmission isn't warmed up am I correct? With a auto it should be instant.

[woundedbrat]

I have heard that the fluid couplings or vlsd take severa rotations for the friction to build in the fluid

[nipper]

Fluid couplings have to heat up to transfer the power. The fact that the car did move does tell you it works. Manuals either work or are locked up. I've yet to see a manual not work, they just dont work instantly.

 

In order for the fluid to heat up and expand, there has to a speed differential between front and rear. The hook up isnt a hard mechanical hookup, its more like a fluid hook up untill the fluid gets hot enough to transfer 50% of the power. Usually before that happnes the car is moving, the front wheels are off the slick spot, and everything goes back to equilibrium.

 

http://www.wisegeek.com/what-is-viscous-coupling.htm

 

nipper

[bulwnkl]

As I understand it, the manual tranny still uses a conventional mechanical differential, it just incorporates a viscous-type limited-slip unit. Thus, your rear wheels are always getting 50% of the torque put out by the engine until and unless the viscous unit heats up and alters that situation. An open diff should spin the front wheels and leave the rears motionless in the situation you describe. So, the fact that your car moved suggests the fluid was heating up and starting to alter the torque bias.