I took my 2010 Panamera Turbo in for service this Wednesday for a few issues (55k miles under CPO):

1. Sunroof makes crunch sound when opening
2. High noise level in cabin when driving; sounds like transaxle, rear axle or maybe tire noise

The second one is the troubling one, as any number of things in a sophisticated AWD transmission line could make noise. I thought this is going to be one of those things that I go back and forth with service on, them saying noisy roads make noisy cabins and me saying I'd never have bought the car making this sound.

I get a call late Friday from the SA where he says, flat out, your car needs a new rear differential. The issue is rare enough that there isn't a part in the states and they've had to ask for one from Germany. Wow, I think, that's pretty rare. Then, I think, what could lead to a sports car, with a truck-sourced drive train designed for all kinds of hooligan driving, destroying it's own locking diff? I'd guess a few too many launch control starts, of which I'm responsible for none.

On top of it, he says, once the took the belly pan off they spotted an oil leak at the engine/transmission junction, so looking at a main seal at a minimum, after an engine pull (or maybe just a tranny drop, not sure how it works in a sedan).

Side note: I had a 2000 Boxster that begged for a main seal every 18 months or so. Finally sold it after 5 years of putting those in and getting real tired of it. A pattern?

SA tells me it looks like 1st or 2nd week of January before I'd see the car back. Yikes. If so, that would make 5-6 weeks of in-shop time for a used car I bought 6 months ago. Not a great track record so far.

 

Wow. That is disappointing to hear. Luckily it's under CPO.

I don't remember reading any other reports of rear diff failures or main seals on PTTs here or on Rennlist. It may just be bad luck.

Nevertheless, your experience does reinforce the suggestion to ensure you have warranty coverage on these cars.

 

I could be wrong but I believe that is sometimes how the rear whistling noise is taken care of.

 

While this is definitely frustrating for you, I don't think you need to worry about it in the future. If it were a common problem with the car they would stock the part in the US.

 

THAT is a really good point!

 

Is the issue part of PDCC? thought the diff came with that with PTV.

 

The dealer should be giving you a loaner car during your downtime. That's normal practice. No need for a used car.

 

Dropped by the dealer to pick up a lender (didn't need it until now) and visited the PTT in the service bay. As you can see, it's in good company.

Chatted with the tech (in the pic) for a few minutes as he slowly pumped new oil into the replacement diff already in the car. He showed me the old one, in the shipping crate, which looked dusty but intact and dry. He said the sound I was hearing was the pinion and related bearings starting to wear to the point of audible noise and it was only going to get worse. I asked what leads to such a heavy-duty part getting to this stage and all he could offer was a bad unit initially or abuse, which hard starts (launch control) are an example of.

He then took me up front and said, power train abuse evidence starts here (points at crankshaft/tranny junction) and makes it's way down there (points at the rear diff). Uh, yeah, well we're here because the diff is trashed and you've spotted a main seal leak. So, I guess I have my answer.

Luckily CPO coverage should take care of all this. The SA told me, after I floated the theory that we're looking at a car that's been abused and showing the signs of it, that the PO, who he knows well, "doesn't seem like that kind of guy".

BTW- the underneath of a PTT with it's AWD systems and sport exhaust and other systems is a staggering maze of pipes, linkages and joints. It's an amazing piece of technology. To get to the diff they had to pull the exhaust & disassemble the entire rear wheel linkages including braking system.

Outlook is another 1-2 weeks on the rack as they pull (excavate? unearth?) the tranny to go looking for the oil leak that should only be a main seal, but could honestly be anything. Then, some time on the sunroof for why it goes 'crunch' when opened.

For those curious, that's a new 918 Spyder in the pic that was being prepped for delivery. The white color is a build-to-order white, adding just a little more to the $990,000 price tag.

 

Wonder if they can get into the engine ECU and tell you how many times the car has been launched, or otherwise redlined. Might give you a clue. They say that PDK itself is designed for 3000 launches. Not sure about PDCC or the rear diff though.

 

If I were you, I would've at the very least, have them trade the PTT for the 918 for all the pain and suffering, even exchange.

Try that with your SA and see how it goes, if anything give them my name.

 

Another week, another call from the SA, and we're still not there yet. Isn't this fun?

The diff is all done that's considered a wrap, until test drive verifies proper ops. Sunroof status is unknown.

They pulled the PDK and have found a hydraulic leak at the dual mass flywheel, not the engine main seal as suspected. This is good news, in that it tells me the engine is still tight and the crank is straight, but bad news in that he nor I have ever heard of this problem before. In fact, the SA said he's never seen a PDK out of a car before _ever_ for service, and he's a veteran of the dealership.

Quick research reveals: the dual mass flywheel is a standard part of the PDK that uses springs and hydraulic fluid to (probably) dampen the pulses when shifting gears. There is no torque converter in a PDK. All flywheels store kinetic energy and this one also has a system to store & release spring energy inside the flywheel. It's hard to find any hard technical data on the the PDK works at all on the web, so I'm putting together an educated guess.

It's also hard to find any reference to a failed dual mass flywheel. In fact, I found none. Hmmm.

I asked the SA to please have the clutch packs inspected at this time as they should be right there. Right? Anyone know how hard you have to dig to get to the wet clutches in a 1st gen PDK? By the videos, it looks like they are right behind the flywheel, inside the transmission housing.

So, a blown hydraulic system in the flywheel and a blown electronically lockable rear diff. Starting to add up to drag racing abuse, I'd say. The SA and I will be having a heart-to-heart soon.

 

Thanks for the information . Looking forward to pdk details .

 

SA called Saturday. The clutch packs are non-serviceable at the dealer. They aren't even visible; you'd have to crack the case open to even see them. In short, the wet clutches are a lifetime part and not a repair item. If your PDK has worn out clutches, the PDK is at the end of it's service life.

SA said that all you can see when you look at the thing on the lift, besides the big transfer housing that comes off the side for the front axle driveline, is a spline shaft with the dual mass flywheel. Starter pokes out where you'd expect it. That's it.

Flywheel service included replacement of the flywheel with a factory new part, in whole.

I did a little reading on-line about the PDK and it turns out ZF did two different ones initially, one for cars like the Boxster/Cayman + 911 and a different one just for the Panamera that move the input shaft up on top of the housing to fit the low profile of the car. Next time you get into your Panamera and winder why the transmission tunnel is so tall, elbow height, that's why.

 

Time to wrap up this saga.

Picked up car last night at Service. They had it gassed up and washed, a minimum level of concierge care at this level, IMHO.

Service invoice is 4 pages, all zeros to me, so that's nice. The transaxle issue notes include the tech adding ATF & oil to diff and giving the chassis a listen. They then pulled the brakes and the diff to replace. I think they then had to realign the wheels (ACC ALIGNMENT). Parts list include lots of screws and bits, two red axle diff part numbers (970-350-021-1X) and (970-350-021-1U) and lots of labor.

Sunroof: no problem found, but I think they lubed it then tested, not the other way around.

Flywheel: Problem spotted by tech during repair, performed PDK R&R. Parts list is short, with the main one being the flywheel itself (970-114-020-51). Google says about a $2,000 part.

Also, they found an unidentified door trim part on the driver's door to replace.

So, how's the car after after the service? In a word, amazing. The hookup of power off the line is a big improvement, with power delivery coming on at 1200-1300 RPM (before it was 1500-2000). That's got to be the flywheel. The power train is smoother than ever, with no whine or throb coming from the back (diff). Putting the power to work is really enjoyable now, without the sense of a 'drag' or lethargy to it. This must be what these cars are like when closer to new.

However, nothing is ever perfect: the car was returned to me with a dead key (or dead battery) in the ignition and the tires were 10 lbs flat.

 

Those two part numbers are for the rear diff assembly. The one with the X at the end is remanufactured. Not sure of the U. Looks like they swapped the whole thing. Mine has a small leak at where the left axle meets the diff. It should be only a seal replacement. At 26k miles these things shouldn't be happening. I can't understand how JD Power rates this car as the one with least issues. I have owned so many other luxury brands and none of them creaked or need a bushing and seals ever.

Starford,
Would you mind sharing the service invoice? I'm interested to see the details of the PDK work as well. I have some noise and vibration from the front that comes at low rpms. Thanks.