Hello,

my visco coupling has died .
I didn't uninstall it from my car, but I know that some visco-couplings can be opened to be filled again with a new fluid.

Is that possible with our viscous or have I got to change it ?


Thank you.


PS: Yes Ilike my car AWD.

 

i believe you can change the fluid in the diff but i would suspect you have a more serious failure than just the fluid

 

No, you can't open the viscous coupling. It is a sealed welded unit.

 

^that doesn't mean you can't open it, just means it may not go back together easily

 

How do you know it is bad? I "tested" mine the other day.

On a smooth concrete floor, i jacked up the rears with a good floor jack on the cross member just in front of the motor just enough to get the rear wheels off the ground. put two pieces of 1x4 trim (3/4" thick) in front of the front wheels. Got in started it up, PSM off, First gear and let the clutch out slowly. i could feel the front starting to pull then they release somewhat and the rears are spinning. Clutch in, clutch out, i can feel it trying to climb over the 3/4" trim but not enough torque to actually climb over it, not even close. Took it up to 3K rpms and it still would not climb over it. kept it there for like 30 sec thinking the fluid will heat up and increase the torque to the front wheels but not appreciable change.

Can some of you other member try this and share your results? i have been looking for a way to check the health of the AWD. This may be it but i only have one data point.

Edit: Do this at your own risk, if it hops off the jack it may end up in the bedroom.

 

Please don't do this. This is not the way to test the AWD system. In fact is more a way to damage a perfectly fine viscous coupling because it subjects the viscous coupling to serious difference in speed between the driven discs and the driven discs.

 

The viscous coupling has no field serviceable components. There is no facility for changing the fluid.

If the viscous coupling has died the front diff must be replaced. That is unless the viscous coupling can be removed from the diff and replaced as a separate item, which I do not think is the case.

 

Well, I understood it didn't work when I tested my breaks...

It's not easy for me to explain because I don't know the english word for the device, a "roller brake tester" ? Does it mean something for you ?
You put the 2 front wheels on the tester, and because it's a 4 whell drive car, you have to place the rear wheels on free rollers.

The problem is that when the front wheels test was done, it's been impossible to get the car out of the rollers... There was not any power to the front wheels.

Driving, the car was not as before, it was not as safe, as easy, but I didn't know the reason why until the brake test.
I was driving it as a 4wd, and it was just not the thing to do...

I think you don't have this in USA, but here in France, we've got many many "rond points", like this:



and when you use to "throw the car" inside it to drift a little, it's a little surprising to have a 2 wd insteade of your 4wd...

Thank you for your answers.

Maybe that, even if Porsche didn't plan a system to fill again the viscous, there is a way to change that fluid... Let's dream...
If somebody knows...

If not, I will have to buy another one, but no new...

Do you know somebody that doesn't want it's viscous anymore ?

To my knowledge, it's possible to change only the viscous.

 

Vaguely I recall someone who had his Turbo tested on some kind of a brake tester that used rollers.

The car darn near jumped off the rollers.

There is a "test" of the viscous coupling spelled out in the factory manual.

The test conditions I think will prove of some value.

Test only with the viscous clutch at room temperature.
Test speed of the front wheels between 3km/h and 5km/h (wheels driven by rollers of roller brake tester). Test duration 3 minutes; record the traction every 30 seconds.
Repeat measurement after viscous clutch has cooled down for one hour.

The manual goes on to offer the test steps and what the traction at the front wheels should be at various test speeds (3kh/h and 4km/h) and at the 6 test points separated by 30 seconds.

BTW, I also see the viscous clutch can be removed from the front diff.

Whether the clutch can then be disassembled and rebuilt or just replaced I don't know from the info in the factory manual.

Oh, the AWD system is not intended to move the car using torque to the front wheels only. The local Porsche techs told me a surefire way to ruin the viscous coupling is to get the rear tires stuck in the snow and sit there and spin the rear tires. The viscous coupling just overheats and gets ruined.

To remove the car from a brake roller tester with the rear rollers free spinning the car must be pushed off the rollers.

About roundabouts... The car does not have an AWD system that behaves similar to those of say rally cars. If you expect when pitching your Turbo sideways to experience the distinct pull of all 4 wheels/tires you will be disappointed. There are YouTube videos of 996 Turbos in the snow and while the rear tires are spinning madly the front tires are either just barely turning (not even spinning) and in fact the inside tire is stationary if the driver is spinning "donuts".

For all practical purposes I think it best to consider the 996 Turbo a RWD car albeit one must keep in mind it obviously is an AWD car when/if he encounters situations in which the rear and front wheels/tires can turn at too widely different speeds.

 

Something like this?