Third-Reef

A crude version of the test: back wheels off the ground with the car resting on a decent floor jack that is pointing forward jacked up on the rear cross member on flat smooth concrete. you should be able to push the car forward or backwards and it will roll on the front wheels and the jack. Now place a 1x4 piece of wood in front of each front tire. Start the car and let the clutch out slowly in first. it should try to climb over the board but not quite get over it (my results). This test indicates that the viscus coupling is not frozen and it does transfer some torque. i think this is the best you are going to get easily. You could get fancy and calculate the torque provided by the height of what it will climb over.

Complete this at your own risk!!!!! Be careful and have lots of room and no people around the car.

greencalex

Did you get much/any spin of the rear tires before the fronts grabbed?

To be honest, I'm a little hesitant to do the floor-jack thing. Despite having seen a number of YouTube demos on other types of cars, it just seems scary to me...

Dock

I'm more than hesitant. I wouldn't do it.

Carlo_Carrera

Doing scary things makes life worth living.

Third-Reef

The rears spin free and the fronts pull. You can feel it as you let out the clutch and it tries to climb over the board. As far as scary goes, this is nothing like turn 1 at Laguna at 130 on stock suspension. Just make sure there is ample room in front and be sitting in the car ready to push in the clutch and hit the brakes. It's really no big deal at all.

greencalex

Happy Holidays to All!

So after an incredibly painful experience thing to get the center viscous clutch changed (literally no one in my area had ever changed one, and all took the position that "we've never seen one of those fail, so it is probably fine"), I finally brow-beat the dealer into swapping for a new one.

Long story, short:

Before swap: two driver's side wheels off the ground, trans in neutral; takes a couple of turns of the front wheel before the rear starts to turn; couple of more turns before both wheels are turning at same rate (this after having driven for a few miles to warm-up the viscous fluid).

After swap: rear locks to same speed as front after maybe 20-degrees of rotation; the point where the clutch locks is very sharp; no slop at all (same warm-up procedure).

Before swap: just one front wheel off the ground; turning requires about 30lb-ft of torque after several rotations of the wheel.

After swap: over 50lb-ft after 20-degrees of rotation, and goes up from there; after a few turns, torque is in the 80lb-ft range.

Note: if any of the various mechanics had any experience with this system, they could have determined immediately that my viscous clutch was shot. The dealer mechanic claimed that Porsche North America was equally clueless about what normal operation of the system was.

So now we know...

Cheers!
Alex

Carlo_Carrera

Thanks for the info.

Third-Reef

Do you notice a difference in how it drives? Will it spin the front wheels at all? On wet or snow? Was it worth it. I have been noticing how small the torque transfer seem in my car with 90K on it. Always have wondered about this .

greencalex

From the driver's seat, it is hard to tell (at least for me) whether the fronts are spinning, but I have noticed that in a couple of spots where I often spin the rears a bit, that does not seem to be happening now. I'm now wondering if I might be able to get a set of rear tires to last a little longer...

I've not done much snow-weather driving since I got the car back, but expect that the difference will be noticeable (I started to suspect the viscous clutch when I noted that the car never seemed to get any front traction in situations where I think it should have).

Mind you, one reason I really wanted this repaired is because I have to figure that the PSM system has strategies built-in to it that leverage off what the AWD system is supposed to be able to do. Last thing I want is for a computer to be getting inputs that it does not consider to be "normal." So to me, this fact alone makes it worth doing the repair.

Kevin

Thanks for posting the update.. Can you post the repair cost for future front viscous failures? Part prices and labor hours and rate would be nice. Cheers

greencalex

Part was around $1.8k.

Labor was at a crazy high rate (dealers being what they are).

I had other work done, and they did not break the time down by job, but my sense from talking to number of shops was that this was a 6-8 hour job.

Carlo_Carrera

The VC at $1800 is full dealer markup. They are available for substantially less elsewhere.

The part number is 996-339-021-02 for anyone thinking of replacing it. I am also pretty sure Porsche sources it from a vendor so with research it my be purchased directly for even more savings.

greencalex

All true.

From various discount places the part could be had for $200-$300 less if one shopped around.

In my neck of the woods, however, all the shops charge close to dealer prices for parts, or (if you supply the parts) charge you a higher hourly rate; given the amount of time involved, the "parts" cost would have been close to the full dealer price, even if I had an independent shop do the install, and bought the part at a discount.

If I had been willing to tackle the job myself, I would have bought the part from a discounter.

Carlo_Carrera

I totally understand. It is a catch 22 and a very tough DIY job without a lift.