steve_eo

I've recently bought a C4S (had a 89 C4 and have a Audi S4). Since I'm aware there are differences in the 993 AWD compared to the other two cars...I'm trying to get a feel for the differences.
I've been trying to get the front wheels to spin....or at least to feel them grab. But I just can't seem to feel them do anything. I've tried putting all four wheels in gravel and then accelerating hard-this just makes the two back wheels spin. I've tried putting the drivers-side wheels on pavement and the passenger-side wheels on gravel....ABD kicks in but I still don't feel anything on the front axle. Yesterday it was raining lightly....resulting in very slippery roads. I actually had to be very careful while stepping on it in curves and off the stop lines. In the '89C4 or in the S4 I very definitely would have felt the fronts grab in all the above conditions.....but I don't in the 993.
I've got 265/35/18 on the rear (as opposed to the spec'd 285/30/18) and 225/40/18 up front. The 265s' are from a C4...will this small tire size make a difference? I'm aware the back should be a bit smaller (and they are) to allow the AWD to work....but there just seems to be nothing driving the fronts.....
Is there a way to test the AWD (short of going to the dealer)?
Thanks for any help...
-Steve

Steve Weiner-Rennsport Systems

Hi Steve:

Under slippery conditions, you should feel the front wheels getting power as the rears slip; its a progressive sort of thing,.... If the fronts are not grabbing even in the wet or on gravel, then you should have the Dealer check this out. Your current tire sizes will not affect that. Bear in mind that the 993's AWD works differently than the S4 and 964 cars; these progressively send torque to the front wheels as the rears spin. You should feel it in the steering wheel as the front starts pulling.

I've seen one car (993TT) that had a broken viscous coupling due to drag-race type starts and therefore was a RWD car until we replaced that unit. The AWD coupling is sealed and cannot be repaired; one simply buys a new one.

steve_eo

Steve, thanks for the reply.
It sounds like mine is shot....wonderful news
Any idea on how much this will cost? What is the VC worth? Maybe I can find a used one....but then again maybe it's broken too....
Could I install something like that myself? Or do I need special tools etc?
[edit] I called the dealer...new ones cost ~$1000CND. I didn't ask about labour...I was too afraid.
-Steve

JohnM

The C4/C4S have a very definite RWD feel to them, there's probably nothing wrong with your VC - it is pretty difficult to kill one though they can be damaged by running the car on some types of 4-wheel dyno.

Steve Weiner-Rennsport Systems

Hi Steve:

I would not jump to any conclusions until either a Dealer, shop, or a well-experienced person has passed judgement by driving your car. These AWD systems do feel rather transparent, and very different compared to the cars you have previously owned.

The VC unit is very tough as I've only see that one that was broken,.....don't forget that was a 400+ HP car.

Get some more qualiified input on this.

DJ

When I first got my C4S I thought the AWD was broken too. Here's how you can test it: put the car on a lift (so that all four wheels are off the ground, and the car is secure), start the car, put it in first gear, and let the clutch out (at idle speed). Watch in amazement as all four wheels turn. Interestingly, the fronts turn much slower than the rears (about half speed). If you stop one of the front wheels from spinning (by using only moderate pressure with your hands), the other front wheel will slightly speed up. Stop both front wheels (this takes a fair amount of effort), and both rear wheels will speed up.

Don't try to stop one of the rear wheels from turning, and don't ask me how I know...

steve_eo

Thanks DJ. I'll probably try your idea later on tonight...after I get my HID kit finished...
Thanks to John and Steve for the info too....
-Steve

boostid

Steve;

You can easily test just by jacking up one front corner and then turn the wheel/tire by hand. If the VC is ok, there should be some resistance, tho it will turn slowly. A broken VC will spin easily, like a 2WD car. Dealer did this in testing my VC when I had service.

graham_mitchell

Steve_eo, the same thoughts run through my mind about my car. But if so many people have felt this way about their C4s, then that is reassuring.

DJ, thanks for the test suggestion. Next time the car is on a lift I will try it.

WillyC4S

When I had my car up on the lift, for the pre-purchase inspection, I rotated the rear wheels and the front tires spun. I took that as confirmation for the AWD capability.

I don't want to start another phobia here, but the part that really buzzed me for a while was that I also had the limited slip option on the
car and this should show up on the lift as having both rear wheels turn in the same direction when they are spun. If it wasn't limited slip optioned, turning one wheel would result in the other turning the opposite direction. My C4S with the limited slip option turned in the opposite direction!

Apparently having ABD deletes the mechanical limited slip and puts in place the electronic braking limited slip. That's what the puzzled
mechanics told me. Any thoughts on this?

Sorry to go off topic on this one.

*****

DJ

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by WillyC4S:
<strong>Apparently having ABD deletes the mechanical limited slip and puts in place the electronic braking limited slip.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Not true. I've had mine all apart, and it has both ABD and LSD. Of course, the clutches on your LSD could be worn, as they aren't really all that tough, as I've heard of a few that were worn. My car had 60k miles, a lot of which were on the track, and mine were just fine.

WillyC4S

DJ,

what happens when the LSD is worn? Do you go back to a normal differential (i.e. if you spin one wheel on the rack, does it not move in the same direction?).

Thanks,

*****