shawsan

Recall a recent post by Kevin noting several things that can deteriorate on a 993tt over time, with specific mention that up to 60% of cars will likely need a new VC sometime, depending on mileage, mods, driving style, etc.

But apparently, its not all that easy or common to have a fully reliable or informative test of the VC's performance. On the one hand, if the VC is fried, that's one thing; simply applying a a torque wrench to the rear and observing that the front wheels don't turn provides the needed info. If they don't turn, new VC is required. On the other hand, to do a fully informative test requires the car be put on a dynamometer, with laptop and porsche software in hand to assess if the VC has an acceptable performance range. Many dealers don't have this dyno equipment.

Thus, on my 993tt, the torque test revealed engagement and rolling front wheels. Moreover, the service agent used a comparator 993tt that happened to be on a hoist at the same time, employed the same torque test, showing that front wheels engaged at about the same rate on both cars. And so, I was informed, your VC looks OK as far as we can determine -- and this was from a bonafide,performance oriented, porsche service dealer. Yet, they also explained that w/o the dyno/soft wear test, they couldn't be sure the VC was operating 100%.

I'm partially satisfied my VC is OK, but don't like the uncertainty it might not be operating 100%. Maybe its only operating 50%, 65%. I guess the obvious response is: if I really care, I should go get someone to do the full test. But I wonder, are others in a similar boat to me. Are there several of us driving around with sub-optimally performing VCs and, if so, is that something to be concerned about.

sfbanchs

i would love to know the answer to this

chris walrod

I honestly dont think there is a definitive -yes- or -no- to whether or not the VC works and to what extent or as a percentage. Of course, there are examples where the VC is SMOKED, much like that of 2wd dyno sessions with an AWD car.

ttAmerica RoadsterAWD

Do a search on viscous coupler and you will get lots of info. From what I can recall, one good way to check for good function is to lift one, and only one front tire such that the other three are on the floor, rotate that front tire by hand forward and you should feel considerable resistance. It is said a warm VC will perform optimally cause the fluid in it is more viscous than when it's cold. The difference in front and rear tire rotation heats up the VC fluid and engages the coupler.

I hope this this helps.

By the way, if you ever seen a VC its just about 8inches in diameter and does not look substantial. I have a brand new one sitting on my bench waiting for me to change my current one out. The VC doesn't appear to be "Porsche" robust......

Jaime

Stummel

What would be the effect of a not-so-good VC?

Less torque to the front wheels?

Less understeer?

ScottMellor

OK you're all gonna laugh at me. Here's how I test if my VC works. Go out on a rainy day. Get rolling across a nice greasy intersection and then floor it. If all 4 wheels just spin and the car does not move, I call the VC good.
Empirical real world non destructive test.

ttAmerica RoadsterAWD

I did something similar....
after it had rained I went onto a grassy wet field, I guess it doesn't have to be wet, Had my wife check if my front wheels peeled out in unison with my rear wheel peel out. They didn't.

Felix

Not sure how quickly it heats up to start the transfer... that's been the subject of some discussion in previous posts.

ttAmerica RoadsterAWD

Well, not to start another debate, but why would Porsche install a heat sensitive activated viscous coupler if it took more than, say, 2 seconds to engage??? Seems awfully dumb-why bother??