tim you have 1 more rep point that me brah. sup with that.

 

Tim,

Tell me what happens to the center vc when one rear wheel is spinning twice as fast as the front wheels? Now when you add a lsd how does that help the situation when that single rear wheels isnt spinning like mad?

There is a good reason I changed my front tires to be more or less identical in diameter to the rears.

You reply like no one could possible understand anything as well as yourself, so please explain to all us simpletons.

Might want to turn the dick volume down a notch.

Paul

 

One or both rear wheels can not spin any faster then the input speed of the pinion, lsd or not. With that said the pinion gear has the yoke directly bolted to it, that has the cardan shaft bolt to it. If that is understood then we agree that the rear diff and front diff are spun at the same speed regardless of what the wheels are doing.

This statement sums it up for me.
" There is a good reason I changed my front tires to be more or less identical in diameter to the rears."

It proves you do not understand why the wheels are staggered. The wheels are staggered to heat up the "vc". How you wonder? Well the rear axle is spinning faster then the front needs to to go the same speed. How can that be you ask? Well the "vc" does not lock. it never will unless the plates get galled enough that they fuse. Now the difference in speed must create friction. one by product of friction is heat that heat thickens the viscous fluid, now the "vc" is ready to react when it is needed. How does your system work when you removed the very thing that makes it work?

"You reply like no one could possible understand anything as well as yourself, so please explain to all us simpletons."

I replied so when someone does a search they will find the truth, not a "wiki" rendition..

 

The front and rear diffs are not directly connected, the vc is between them. The only way the vc heats up and allows power transfer is when the rear wheel spins faster then the front. Without a rear lsd it is very easy to have this happen. The vc heats up very fast, does not need the different size tires to do this. Porsche did this to increase power transfer as speed increased to improve stability and high speed handling.

The vc fluid changes state towards a solid when heated, nothing to do with the plates touching like in a clutch pack diff, you seem to not understand how a vc works.

Tell me again what about the wiki quote is not the TRUTH?

 

So you are saying that all those vids and my data are all lies? As I stated before cut a "vc" open and see for yourself.

 

I am in my workshop working on my car, I was looking for some part and I came across the remnants of a front drive.. It started my mind going again...

Quote: Basic from Wiki..

" The viscous type is generally simpler because it relies on hydrodynamic friction from fluids with high viscosity. Silicone-based oils are often used. Here, a cylindrical chamber of fluid filled with a stack of perforated discs rotates with the normal motion of the output shafts. The inside surface of the chamber is coupled to one of the driveshafts, and the outside coupled to the differential carrier. Half of the discs are connected to the inner, the other half to the outer, alternating inner/outer in the stack. Differential motion forces the interleaved discs to move through the fluid against each other. In some viscous couplings when speed is maintained the fluid will accumulate heat due to friction. This heat will cause the fluid to expand, and expand the coupler causing the discs to be pulled together resulting in a non-viscous plate to plate friction and a dramatic drop in speed difference. This is known as the hump phenomenon and it allows the side of the coupler to gently lock. In contrast to the mechanical type, the limiting action is much softer and more proportional to the slip, and so is easier to cope with for the average driver."

Quote from Basic,

"Again, if you feel your awd doesnt do anything or very little you probably have a worn out viscous coupler."

Wiki: States "it relies on hydrodynamic friction".

I will leave you with this question.. How does hydrodynamic friction "wear out"?

 

What happens is the fluid breaks down in a condition called gellation. The fluid breaks down the plates during the heatup and solidification of the fluid. These little bits of metal create issues with the fluid and eventually fail the unit.

Lots of information regarding this available on the net, VC are not uncommon. These units wear out, when they do you gradually lose transfer of power to the front wheels. Not sure if they could possibly be rebuilt, when mine goes I will likely figure that out.

Some more info I found

"

1. If you refill a VC so that it is full it will burst its seals. Never refill so it is full. (The proper percent air is 84% to 86% according to an estimate from another expert familiar with Viscous Couplings but this percent cannot be confirmed yet.)
   
2. The plates inside the Viscous Couplings have microscopic burrs on them that are critical to the proper torque transfer of these units. This means that the plates wear out and cannot be reused!
3. Since replacement plates are not available, this means Viscous Couplings should not be rebuilt until a source of replacement plates can be identified.
4. Any viscous coupling under pressure is likely a bad viscous coupling! If you open the unit, and a lot of VC juice comes out, the VC is likely bad.
5. Viscous Couplings have a useful life of 60,000 to 90,000 miles. After that, they are worn out and should be replaced. This makes it sound like they should be replaced as often as your clutch! "

 

Colorado drivers, take an extended test drive to Squaw Pass road in Evergreen and test the winter performance for yourself on a nice cold day, or slushy day.

I-70 from Evergreen to Den is a much different drive than over the Loveland and/or Vail pass on black ice or slush. Besides we haven't had a hard winter in a couple years in Colorado. Neither has Canada btw. Or Midwest. I drive a Carrera for ten years over 100k miles as DD (with 4 wheel studded snows) and it was good. I live in Evergreen at 8500' elev w ten miles of mtn roads to I-70, and have Range Rover for DD now. It's always better to have a true 4WD than AWD and tires are very important as is driving style. Most ppl have never owned a true 4WD so comparisons are subjective. I have a friend in Breckenridge who drives an older C4S all seasons and is good. Jmo

 

All though all this information seems like great information, however if you have reduced the front drive down to its components you would know that this info is completely useless as Porsche uses a sealed unit. If the "VC" is such a magic unit why does Porsche now use a simple clutch type with a pwm controller?

 

epic lol

 

Pretty much all VC units are sealed....no magic it is what we have in these cars. I don't see how it's useless to discuss how this works.

Why does Porsche now use a electronically controlled clutch? probably the same reason PDK is being used, it's called progress.

 

They can be rebuilt. I have some experience with 3000GT/Stealth turbo transmissions (built by Getrag.)

Here's a site that rebuilds them for those cars:

http://stecouplers.com/recharge/modu...index.php?id=9

Don't see why they couldn't rebuild ours too.

 

Thanks for this feedback. Closing the deal on a '02 Turbo today, should arrive with plenty of time to test it out on wintery mountain roads. Looking forward to it!

 

Awesome information.

These forums are great for in-depth discussion like this. Also, kudos to everyone for being complete gentlemen during this most informative and somewhat "charged" discussion.

 

So can a 997 front diff be put on a 996 turbo?