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Old 10-28-2000, 10:24 AM   #1
JGard
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Question Question about viscous limited-slip

Ok, i've read that a viscous slip diff uses plates and fluids to function. so, basically, isn't this just like throwing a slushbox automatic tranny in the car? or are these much more responsive than a torque converter? or does the auto tranny seem sluggish just cause of the way it shifts (meaning it's not the torque converter at all)? i will say, i haven't driven an auto RS, but i do know how they feel in other cars...
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Old 10-28-2000, 10:49 AM   #2
munkis
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A torque converter is more complex than a viscous coupling, car manufactureres a long time ago used viscous couplings b4 tourqe conversters were invented, but they found they overheated to easliy.

Get a book about auto trannies and youll get a good description on the two.

Jay McDade
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Old 10-28-2000, 10:52 AM   #3
JGard
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i understand that it is more complicated, but my question was about the "slushiness" of both the torque converter and the viscous coupling, since they are using the viscosity of liquid to turn plates (essentially)...

[This message has been edited by JGard18 (edited October 28, 2000).]
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Old 10-28-2000, 02:01 PM   #4
Jay_UK
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In theory no (once the plates have locked)

Otherwise you will fry the fluid.

There will be some slip/loss at first.. this lost energy/power goes into heating the fluid.

Hence the viscous diff isnt instantly acting.. there is a slight deal (slushiness?)

J.
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Old 10-28-2000, 02:03 PM   #5
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ok, that much makes sense... like, about the locking and such. but what about while driving, and it has to lose some power from one end of the car to the other? cause then they won't be able to spin at the same speeds, correct? or am i missing the point on that one?
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Old 10-28-2000, 02:16 PM   #6
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1st of all sorry if I offended anyone (I'll use the "I'm french" excuse again here;-), I'm just trying to understand too !

2nd, I'm not sure on the details, but don't we have some direct connection from the trans to the wheels (ie front wheels), so at worst it would be just like a manual front wheel drive car w. some power loss from the center diff ? So we would not feel the slugginess since it would be just between the front / rear wheels under slippery conditions ?

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Old 10-28-2000, 02:17 PM   #7
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see, i thought the center diff. was the same concept as a transfer case. where the tranny went to that, and then split out to front and rear. but am i wrong again?
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Old 10-29-2000, 12:28 AM   #8
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It's not the viscosity of the fluid that determines auto tranny shifting, but pressure. Most shift kits are used to modify the pressure that the shifting mechanism sees so that shifts are quicker and harder. The center diff on our cars are different in that it relys on the viscosity of the fliud to "lock" up. When the plates (F vs R) rotate at different speeds, it causes the fluid to get thick and therefore transmit power to the rear.
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Old 10-29-2000, 12:28 AM   #9
rao
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It's totally different. In a viscous limited slip, the fluid that is used has the unusual property in that it "stiffens" up (get your minds oout of the gutter) when it gets hot - and it is this property that is used to make the plates rotate and perform the limted slip function. A torque converter uses conventional oil to build pressure to make the tranny work.
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Old 10-29-2000, 12:31 AM   #10
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ahh, thanks, that's basically what i was looking for.
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Old 10-29-2000, 12:44 AM   #11
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Quote:
Ok, i've read that a viscous slip diff uses plates and fluids to function. so, basically, isn't this just like throwing a slushbox automatic tranny in the car
can someone explain this to me ?
I always thought that 'viscous limited-slip' was for 'torque transfer' in differentials (left to right or front/back for AWD), so how does that have anything to do with a slushbox? After all we DO have a viscous diff for the AWD .. right ? And there's no sluggish auto tranny feel to my 5spd RS.

(hehe maybe it's because i'm french, i'm loosing a nuance in the question or something ;-)
Thanks
Curious Kwez
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Old 10-29-2000, 12:47 AM   #12
JGard
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i'm basically curious as to if there's any power loss in the center diff. because it uses fluid (a la auto tranny) in order to move one set of plates to another. apparently though, it's oil in the torque converter, but same idea (almost). not to be a jerk, but do you know exactly how a viscous diff. works?
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Old 10-29-2000, 09:04 PM   #13
Kwez
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hmmm, you could be right...
hey you super subie tuner guys out there, someone must know the details on this !!
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Old 10-30-2000, 09:12 AM   #14
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The way I understand it:
Tranny delivers power to the center diff, splits front and back
the back is split by the rear diff
same for the front.
the LSD's(center and rear? I know it's at least rear, and wouldn't make sense w/o the center otherwise the power would just go to the front) transmit power w/o using the viscous fluid normally. Only when one wheel starts to spin faster does it heat the fluid and make the other wheel spin the same speed. This is why it doesn't feel slushy. I really don't understand the exact mechanics, but from everything I've read, this is how it works. Trey's done alot of work w/ the system(AWD to RWD), maybe we should ask him...
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