Yeah looks like these tires were a bad choice. I was told they're good. I won't be buying them again!

 

hey drew, we all are entitled to that mistake once.. or how else would "we" know.

 

holy ****.
holy ****.

 

Oh, I forget to mention there is a test to confirm the viscous coupling to the front diff is working ok.

Here's the test steps:


Test conditions
• Test only with viscous clutch at room temperature.
• Test speed of front wheels between 3 km/h and 5 km/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.
top of page
Checking function of installed viscous clutch
1. Connect Porsche System Tester 2 and select −Actual values− menu (PSM speed).
2. Drive front wheels of the vehicle onto the roller brake tester.
3. Switch the engine off, set the hand brake and shift the transmission to neutral.
4. When the brake−tester rollers have started, switch the ignition on and press the Continue key » of the Porsche System Tester 2. The Tester then returns to the point at which diagnosis was interrupted.
5. Drive front wheels by means of the brake tester rollers at a speed of 3 km/h, 4 km/h or 5 km/h.
6. Measure traction 6 times in three minutes. Measure the first traction value after 30 seconds operating time, then carry out five more measurements every 30 seconds.
7. The viscous clutch functions properly if the traction of the front wheels lies within the limit curves in the diagram, depending on the drive speed of the roller brake tester rollers.
Diagram for roller brake tester − speed 5 km/h:


If you want to the diagram for the roller brake test plots let me know and I'll put them into some format I can post.

 

withdrawn

 

I don't have a Porsche System Tester 2 or roller brake tester.. What if I jack the rear of the car up and see if the front tires pull the car?

As for the dyno, a mustang AWD dyno's rollers are linked together ensuring same wheel speed front to back. This wont tell me anything. Putting the car on a AWD dyno that doesn't connect the rollers will surely destroy my front diff if it's not already.



holy ****.?

 

jack up one front wheel leave ebrake on and in gear. turn the front wheel by hand.if you can turn the wheel your viscous coupling is shot.

 

be interesting to know what goes wrong in the sealed system where none of the two halves actually touch.

 

The test steps spell out very low speeds to test the viscous coupling's proper function. I would not have any concerns about doing the test as per the steps given -- or an updated list of steps (the ones I supplied might have been superseded with up to date steps) -- and with the proper equipment.

In your case, relax.

The front diff and viscous coupling are working fine. The fluid in the coupling is lifetime fluid. When the coupling fails it makes noise -- a bearing fails -- or it leaks.

Barring a bad viscous fluid coupling out of the box the usual cause for failure is a bearing gives out or the unit is damaged from improperly towing the vehicle.

 

..only to add to that the possibly very "real" notion there is a front to rear bias that must be adhered to so that it ( the vc ) isn't under undue stress from running an incorrect rear to front tire size. i was always under the impression that fluid could indeed be refilled. is that not so?

not that my rwd really cares any more but seriously wondering. that fluid is about as lifetime as porsche's coolant

 

I too have heard different things about the fluid.. Maybe it is lifetime. IDK

As for tires, my car came with the standard 'incorrect' size 19s (305 rear, 235 front). I wonder if running these tires for 75k miles is an issue.

 

there's one guy here i would take his word on proper 19 sizes and its steve ny whatever he says is safe to run for sure. but im sure i dont think that vc fluid is lifetime though.

 

In the factory manual section that details servicing the rear and front diffs I do not recall seeing anything about changing this fluid. In fact unlike the "lifetime" coolant and the fact it is "lifetime" there is no mention of this fluid at all in the factory manual.

As best I can tell the viscous coupling is a sealed/self contained unit that while it may be exposed to the front diff fluid is sealed and the housing that holds the special silicone based fluid is not accessible.

As for deviating from the tire/wheel sizes sanctioned by Porsche there might be other tire/wheel combinations that just happen to fall into the limits implied by what sets Porsche offers. I just haven't felt the need to work out the various combinations of tires and diameters and whether or not they fall within the "limits" determined that can be arrived at by working the Porsche wheel/tire set sizes.

If I felt the need to deviate from the sets of wheel/tire combinations listed by Porsche, to come up with my own so to speak, I'd work the numbers to see if the new tire/wheel combo falls inside these "limits". 'course, some probably dismiss the need to consider tire size differences with this car's AWD system as nonsense and chose to ignore this. And obviously some no doubt get away with violating this as nothing bad has happened yet.

And something bad may not happen. I do not know how conservative Porsche is regarding this metric. Given the number of cars it would have exposure to dealing with under warranty (or a recall) should it mess up I think Porsche would be conservative. (Warranty costs can be huge: In the latest issue of Barron's I read where Ford is having to budget around $1B to cover warranty expenses this year (with about half of that tied to the air-bag recall) so warranty expenses always come in for consideration.)

Even if Porsche was wiling to go the expense of dealing with warranty issues arising from its getting this wrong, no one I think has rejected buying a Porsche car because of the limited number of wheel/tire sets offered by the factory and by default the restriction on the owner mixing and matching tires/wheels to come up with his own set. But everyone takes into account the reports of warranty issues when considering a Porsche purchase.

 

i was fairly sure the front diff fluid can be changed. if it can be opened it can be changed, one would think. but your the 2nd person to say that porsche says its lifetime so there it is.

its certainly lifetime sitting in a corner of my garage having been removed lol. that also affords me the ability to disregard any of that front/rear tire size quandary relative to the awd system.

 

the VC/Viscous-Coupler utilises a separate-special fluid(which controls awd lock-up) held within its case, it is sealed and 'lifetime' (although the fluid fails over time/abuse)
The front differential, which houses the VC has regular gear oil in it that SHOULD be changed regularly.