Rocket Rob

I checked my PDAS locks sound last night. I turned the key on, waited for the hydraulic pump noise to stop, I then cycled the PDAS switch on and off with the windows open in a closed garage. You can hear a ka-chunk when they turn on & off. With that said, I've never heard them with the engine running. If you are hearing a noise that loud, I doubt that is it.

964Lovac

Please pardon my ignorance, but why would you lock the diffs aside from trying to get unstuck from somewhere?

I don't get a clunk, just a light that goes on when I hit a bump in the road/uneven surfaces... Would be interested in lighting up the light in the dash though!

FeralComprehension

That's the only reason- to get under way when it's slippery. The computer will unlock the diffs automatically once the car hits 25 (?) mph.

It wouldn't be fitting for corporate executives and their dates to be stranded in the parking lot of some mountain resort, not in a Porsche!

tokoro

Rob one last question is that normal that when you turn with the pdas on it feels very hard and when you turn it makes clak clak clak and vibrates alot just when turning either side right or left? I heard it is made for going straight and below 25mph.

Ok forget that I touch the ****, I hear it and feel it in normal operating mode I turn on the car and get out of the garage and when turning you feel that clak clak clack, that is the same I heard when in turn on the PDAS not that hard but a little.



Maybe is just that the other owner never use the pdas and now I use it just to see how it function (there is no need to use here) it but im curious, so maybe I damage something also thinking that is always good to use it so the it doesn't get damage.

964Lovac

Haha!

Thank you, I was just curious as I have not used it at all. Just notice the light going off!

Debating whether or not to install the light in the dash

FeralComprehension

(I'm not Rob, but...) Yes, that is normal. Activating the PDAS in that manner locks both the center and rear differentials. In slippery condtions, both rear wheels would spin and at least one front. Since the differential's normal function is to allow the inside wheel to spin at a different rate when going around a corner, 'locking' the differential forces the inside wheel and outside wheel to turn at the same speed, even though the length of the path they travel on is different. The difference has to be made up somewhere, generally at the tire interface, but with the friction-based locking of the PDAS diffs the slip may occur in the clutch pack as well.

I think that's because you have a diff that's partially locked. It could be that your actuators are gunked up and didn't completely retract when the system was deactivated, or there could be some further issue.

If it was me, the first thing I would do would be to try and remove the actuators and examine the lock/unlock action; see if you can get one to retract further or if there's some other obvious issue.

Also, look for the posts on the broken crown gears and see if the symptoms were similar.

tokoro

This makes a lot of sense. Thanks guys I let you know the results.

Poli84

Resurrecting this thread as I have experiencing similar clunking coming from the C4 front diff.

After getting myself worked up thinking it might be the planetary gears, it seems the noise is coming from the front diff position rather than where the planetary gears are mounted (end of transmission).

Symptoms:
Knocking "knock knock knock" when performing low speed left hand turns in forward and reverse gear.
You can feel a clunk coming through the pedals and the centre console where the front diff is mounted.
Feels worse (harder) in reverse gear.

I've checked all suspension bolts, bushings, etc, changed the sway bar drop links over the weekend (bushes were done), and no improvement.

Car does not clunk or knock in a straight line, only when the wheel is turned to the left.

Mechanic thinks it might be drive shafts after a car park drive, but the clunk is too predominant coming from where the front centre diff sits. Perhaps it is two seperate problems?

I see above it was suggested actuators are gunked up and didn't completely retract when the system was deactivated,.

Did this resolve the issue for you tokoro?

Background
I feel this problem has come about after I 'tested' the centre diff switch in a moment of "I know i shouldn't play with this but I want to". Is it possible that the front diff is not quite disengaged? All i did was engage, drive straight for about 3 metres, and then turn it off.
The yellow light in the console does not work.
Other than that car drives great, no clunks and knocks at speed (even turning).

Plugged in to the Hammer Saturday morning and no errors (even though my PDAS light is on).
The PDAS light is a seperate issue i think, it's only been on 2 weeks and I've had the front diff clunk about 2 months. Still trying to diagnose this, will bridge the R34 relay tonight, exchanged an ABS/PDAS control unit Saturday too and that didn't resolve so at least I have eliminated that as a problem.

Thoughts, suggestions?

FeralComprehension

Have you had the front cover off for inspection? A front diff issue is pretty rare IIRC; I'd sooner suspect the front halfshafts. I've heard of the halfshaft retaining bolts coming loose, and of course given the age of these cars the boots can blow and let the joint dry out which isn't fantastic for longevity.

IMO it's unlikely to be the center difflock "failing to retract" as the front drive is always engaged anyway, plus the front diff is an open style so even if the center clutchpack is locked up I don't think you'll get the hopping spool effect you can get when the rear is locked.