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Originally Posted by PV997View Post
There was recently a post where a Rennlister sold his 997.2 GTS at a significant loss after his PDK failed. That post prompted me to document what I’ve found regarding PDK serviceability. Apologies for the length of this but I wanted to put it all in one place for reference.
I’ve had my 997.2 with PDK for few months now after switching from a 6MT. I was considering an extended warranty, mainly due to PDK replacement cost ($15k to $25k depending on the PDK source). There have been many claims that the PDK is not serviceable but must be replaced in the event of pretty much any failure (i.e. a disposable transmission). This is pretty frightening as items like solenoids fail all the time, like any other electro-mechanical device they wear out.
Fortunately, this just isn’t the case and this transmission is very repairable. Although this transmission is complex, it’s not overly complicated and is serviceable in many ways that aren’t readily documented (intentionally I’ve come to believe). Much of the work can be done DIY. I do caution that this info below has been compiled from my research and I can’t guarantee it’s 100% accurate, but I do believe it’s reliable. I welcome any comments or corrections.
A good animation of the PDK can be found in this video from ZF the manufacturer of the transmission. It gives background into the various aspects of the PDK’s operation that is helpful in understanding servicing the PDK:
For reference the PDK model used in the Carreras (and also Boxsters and Caymans) is a ZF model 7DT45. 911 Turbos use a ZF model 7DT70 which is identical to the ZDT45 except it has a heavy duty clutch. An excellent technical white paper from the manufacturer (ZF) can be found here:
Unfortunately it looks like this paper is now pay-walled. I found a copy of it in the wild and can forward to those interested.
PDK Repair
The PDK has two separate chambers, the hydraulic section (red below) and the gearbox section (blue).
From scouring countless posts describing PDK failure symptoms, unsurprisingly a large majority of PDK issues occur in the hydraulic section. This makes sense as the mechanical gearbox section is functionally equivalent to a manual transmission. Short of a catastrophic failure, there just aren’t that many things that will break in normal use. The hydraulic section and associated sensors are the weak link.
Valve Body, the most likely suspect
The hydraulic section includes electro-magnetic actuators (solenoids) that regulate the flow of hydraulic fluid to control clutch and gear engagement when commanded by the transmission control unit. This seems to be the most prevalent failure location, but fortunately they are easily accessible and replaceable by switching out the valve body itself. (Porsche calls this an “electrohydraulic control unit” but anyone who’s ever worked on a transmission will know it as a valve body.) The valve body can be replaced by dropping the PDK oil pan and does not require transmission removal. It can clearly be seen in this photo below, the solenoids are the colored cylinders on the left side of the picture.
A PDK control unit fault code relating to accessing a specific gear (or inability to shift to a specific gear) is very likely a valve body solenoid issue. In addition, there are also electrical sensors within the transmission that monitor responses to solenoid action and report status to the transmission control unit. Sensor failures can also cause faults and are discussed later in this post.
New replacement valve bodies can be sourced directly from Porsche (~$1700 discount at Sunset Porsche, list is $2800), remanufactured units are available from China (~$850), and used units can be found on Ebay from dismantlers (~$500). This is a universal part for transmissions used on 911s, Boxsters, and Caymans. The 997.2 part number is 9G1.317.897.00 (for 2009-2012 Carrera, Turbo, and GT3).
There are also other identical looking valve bodies available from Porsche under part numbers that apply to different years: 9G1.317.897.05 (2012-2015 911), 9G1.317.897.010 (year unknown), and 9G1.317.897.35 (2012-2015 911 and 2014-2015 turbo/GT3). It’s not clear what the difference is between these units so it’s probably best to eyeball the existing valve body prior to ordering a new part just to be safe (the PN is on the bottom and can be seen by removing the pan). It looks like the part numbers rolled for later 911’s and that 9G1.317.897.00 applies to all 997.2 PDK models, but this is not absolutely certain.
The valve body is item 11 in this drawing from the 2010 parts catalog:
The 2010 Porsche parts catalog also shows another replacement part available for the valve body, item 14 called the “connector housing solenoid valve” (9G1.398.698.00). This appears to be just a cap on the solenoids as they are only $4 each.
Here’s a close-up shot of the bottom of the valve body:
And here’s the top of it, there is no gasket as far as I can tell. The wiring harness attaches at the slots in the colored solenoid caps.
Here’s the screw tightening sequence and the torque requirements.
See the service bulletin attached to this post for more info on valve body R&R.
To make the repair even more inexpensive, an individual solenoid on the existing valve body can replaced rather than replacing the entire valve body. The PDK transmission uses solenoids from ZF, the manufacturer of the transmission. ZF uses a standard line of solenoids on many transmissions that are color coded to denote solenoid function and characteristic resistance. For example, here’s an individual “orange” solenoid from the PDK valve body, a standard ZF part. This is a genuine OEM part available from a good reputation Ebay vendor in Florida for $40.
There is a calibration procedure that is almost certainly required after replacing the valve body or a solenoid that will need a PIWIS and can be done by a good indy. Aside from this, a failed solenoid can be fixed for as cheap as $500 with a used valve body off Ebay and some DIY labor. It can be even cheaper if the fault code can help isolate which solenoid failed, and replace it alone. There’s nothing special about the solenoids in the PDK, the same parts are used on many ZF transmissions including those on BMWs, Audis, and Jaguars.
Failed Temperature Sensor
Another item that fails often is the clutch fluid temperature sensor. This is noted in numerous Porsche forum posts and a Porsche service bulletin (attached to this post). In this failure the ECU throws a fault claiming the PDK needs immediate service (“gearbox emergency operation” message) even though there is actually nothing wrong with the transmission. It also stores fault codes P0711 and P172D in the PDK control unit. In the 997.2 PDK this sensor is located above the valve body and accessible without removing the transmission.
Porsche provides a temperature sensor repair kit (PN 997.612.930.01) for only $35 that can be found here:
This was a known defective part that was often replaced under warranty (hence the cheap replacement part price). The service bulletin claims you need a special crimp tool to install the new sensor and that only one crimp tool will be provided to each dealership (apparently it is a very special tool). However, there is absolutely no reason the new sensor wires can’t be soldered rather than crimped (using high temp solder to be safe), sealed, and covered with chemical-resistant shrink tubing. The service bulletin goes on to make this completely ridiculous statement:
This is exactly the kind of nonsense that has misled many Porsche owners into thinking the PDK is disposable and they need to drop $20k for the failure of a thirty dollar part. There’s no reason the crimp can’t be repaired or even splice in a section of new wire if the connection is somehow fouled up. Yet some dealership grease monkey will solemnly state the transmission is toast because that is what the bulletin says. It’s completely ridiculous and frankly fraudulent.
Here’s a picture of the new spliced in sensor wire prior to the applying the outer shrink tubing. This area is where the valve body would normally reside if it wasn’t dropped down for the repair.
So again the PDK can be repaired for very little money ($40) and the service bulletin doesn’t call for a calibration, probably since the valve body itself is not being replaced. You will almost certainly need a PIWIS to refill the transmission fluid correctly though.
Gear position sensor failures
This is where things start to get a little murkier. I found a few references to these parts in PDK failure threads but not much detail. This is an electric sensor that measures the position of the control rods that engage gears within the gearbox. The purpose of this sensor is to verify things moved to the correct location when hydraulically commanded via the solenoids. These sensors are also used during PDK calibration as the transmission control unit correlates solenoid movement with gear movement. A faulty sensor will cause the transmission control unit to think the transmission is not shifting correctly.
I found some pictures of the sensors used on the 911/Cayman/Boxster PDK (known as the 7DT45) on a Chinese aftermarket parts website. The website is here:
Only one of these sensors is used in the transmission but unfortunately it’s located within the gearbox itself rather than the hydraulic section. In order to replace it the transmission needs to be removed and the gearbox separated. The picture below shows the location of the sensor within the 911’s PDK (tall black rectangular piece noted by the red arrow). You can see the two black appendages that are attached to the gear shift rods in the picture. As the rods are hydraulically moved back and forth the location of these appendages are sensed, probably using a Hall-effect sensor or something similar.
The output of the sensor goes to a connector that is accessible outside the transmission (green arrow). There may be some troubleshooting you can do by monitoring the signals or measuring resistance on this connector. I find it hilarious that the factory t-shooting guide states that gear oil leaks at this connector are caused by a damaged connector O-ring (a 50 cent part) and the remedy is to “replace PDK transmission”. Give me a freaking break.
Here’s a clearer cutaway shot showing the gear position sensor (black rectangle) and the shift rod appendages.
So is opening the PDK gearbox to replace this part feasible? It’s not for the faint of heart but it does look like it can be done. I previously came across a picture of an open PDK being serviced with the front case half (toward the front of the car on a 911) removed, though I can’t find the photo now. The driveshaft, mainshaft, and pinion shaft all terminate into bearings in this front case as shown in the schematic and cutaway drawing below. Note the right hand side of the three horizontal shafts.
The case separation seam is noted by the red arrow in the cutaway drawing shown here. The front case would be unbolted and moved to the right in this example to gain access to the sensor.
Porsche does sell replacement covers for case access to the driveshaft and mainshaft ends as shown in the figure below (items 3 and 4). (You can also see the front case bolts clearly in this drawing.) The cost of the covers is cheap, about $5 each (PN 9G1.321.360.00). Presumably removing the covers allows access for a bearing press if needed when removing the case.
For AWD models there is a further complication as the forward mainshaft egresses the case where item 4 is shown in the above drawing. I could not find a replacement seal for this through either Porsche or aftermarket, unlike the rear wheel drive halfshafts where seals are available. Perhaps it uses the same one. One poster who has his accident-damaged PDK repaired at a small shop in the UK was told most of the seals are also used on the Volkswagen DCT and can be obtained from them.
All in all I’d say the items repaired/replaced via the pan are much easier to get to than the sensor within the gearbox. The fact that Alibaba is selling these sensors tells me that someone is replacing them so there must be a way to do it. If it came down to a $15k to $20k for a new PDK, I’d at least give replacement a try if there was a chance the sensor was the issue. You really have nothing to lose and the potential savings is huge.
Clutch pressure sensor failure
These are another two sensors that provide feedback to the transmission control unit regarding clutch engagement. I didn’t find posts specifically describing these as failing but there no reason they can’t also. They perform a similar function to the gear selection sensors in that they tell the control unit that the clutch is receiving fluid pressure when commanded by the solenoid. If one of these sensors fails the transmission control unit will think a clutch is not operating properly.
These sensors reside behind the clutch and require transmission removal to replace them. Further, the clutch must also be removed (which isn’t hard if you know the trick). You can see the two sensors here where the clutch has been removed from a PDK transmission; these would normally be hidden behind the clutch. (For reference the gear in the upper right hand corner drives the PDK’s clutch fluid pump.)
Here’s the cutaway view below showing one of the sensors (red arrow) and the associated connector accessible on the outside of the transmission (green arrow). As with the gear shift sensor, you can likely perform some T-shooting via measurements at this connector. The good news is that these sensors are replaceable by only removing the clutch; you do not need to open the gearbox. The harness unplugs from the sensors themselves allowing easy replacement.
I’m virtually certain this is the correct sensor part below (PN 9G1.307.385.05) as it looks identical to those behind the clutch if you zoom in on the earlier picture. This PN does appear in 997.2 PDK parts lists but the location is not shown in the parts diagrams.
I found this picture on a Polish website with a cost of $134 each.
Once the transmission is out of the car the clutch can be removed to get access to the sensors using a homemade slide hammer as shown in the Champion Motorsport video below. They don’t explain how to reinstall the clutch but it can probably be pressed back on using a bolt and stacked flat washers. There may be a trick to aligning the clutch in the spline (I’ve never done it) so it’s probably a good idea to document the orientation of the clutch prior to removal.
Last but not least is potential failure of the clutch itself. The good news is that these clutches have proven to be very robust and don’t fail often. The failures that do occur are usually on heavily built engines (e.g. 30% power over stock) with just too much torque for the clutch plates. At these high torques the clutches slip resulting in highly accelerated wear. There are replacement heavy-duty track clutches available for the PDK from Dodson Motorsports, but they are very expensive, on the order of $12k.
There are different clutches for the Carreras (rated at 450 Nm) and the Turbo (rated at 700 Nm). I could not find any OEM clutch suppliers and only found one Chinese aftermarket supplier. Here’s a shot of what they advertise. They don’t list a price but say to contact them for more info.
This supplier only lists the lighter duty Carrera clutch as available and doesn’t have a listing for the Turbo clutch. Their website can be found here:
I don’t think I would go this route unless I was really desperate as I can’t imagine the quality is anything close to OEM. Plus I’ve got a turbo so I’m SOL anyways. Fortunately these clutches don’t fail often so it’s unlikely I’ll need a new one. If it does fail it’s a good excuse to get the Dodson heavy-duty clutch and a monster engine build
Conclusion
To be blunt, I think Porsche’s “sealed” PDK transmission is a scam meant to separate us from our money. There are many relatively inexpensive, readily replaceable parts in this transmission that could be serviced by qualified shops and experienced DIY’ers. Failure of these parts likely makes up a large majority of PDK replacements. I think Porsche has deliberately withheld servicing information to create an aura of mystique around the transmission, to sucker us into thinking we have no choice but to drop $15K to $25k on a new transmission. I don’t see anything that makes this transmission so complicated or delicate that warrants their ridiculous policy. Frankly, it seems borderline illegal to me, violating consumer protection regulations.
To be fair Porsche dealerships do replace valve bodies on the PDK but there is little information on this available to the general public. I suspect there are also plenty of cases where a transmission replacement is performed by dealers when a valve body would have done the trick. On top of that, the Porsche list price for a valve body (which most dealers typically charge) is nearly $3k. Better than $15k but still absolutely crazy.
As an experienced DIY’er, I will almost certainly forgo an extended warranty and attempt to repair the PDK myself if it fails prior to shelling out big bucks for a new transmission. The odds are really good the transmission can be repaired for less than 10% the cost of a replacement.
Note that pretty much every repair discussed here will require PIWIS service prior to being back on the road. Replacing the valve body needs a transmission calibration, as likely will installing a new clutch. Any repair that removes the valve body (even if not replaced) will require a PIWIS for refilling the transmission. A Durametric can read the codes but it can’t perform the PDK commanding. So hopefully anyone affected is on good terms with a competent indy who can take care of this for a reasonable price. Also note that you’ll likely have to flatbed your car to the indy for the cal and/or fill procedure if you DIY the work.
BTW, it’s very likely a PIWIS is not required if one is simply draining the clutch fluid and not removing the valve body. The reasons are found at the link below, and the author explains in detail why that is the case and the tests he undertook using a PIWIS to demonstrate this. I find his rationale to be very compelling, and it squares with other information I’ve found in researching this transmission.
Next steps
Compile transmission fault codes (readable with a Durametric) to cross reference against likely part failure and the repair process. Any help would be greatly appreciated!
As @PV997 stated in the 997 forum, a lot of the issues regarding the PDK can be repaired. I believe Porsche just find it easier to replace them when under warranty. Maybe less labor costs charged by a dealership?
As @PV997 stated in the 997 forum, a lot of the issues regarding the PDK can be repaired. I believe Porsche just find it easier to replace them when under warranty. Maybe less labor costs charged by a dealership?
Less chances of screwing thing up. It took them 4X in one month to fix my coolant leak.
This post also highlights a serious issue: the need to have PIWIS handy as the last 'tool' to be used in many - heretofore simple - service tasks (like fluid changes.) 'Back in the day' a simple o'scope, multi-meter, wiring diagrams, and a bit of research were the essential tools needed to reverse engine some of the 'factory diagnostic tool' functionality. (We - the 928 community - did this over the last few decades for the 928.) But, these days it might take a protocol analyzer and some non-trivial software hackery as well.
The first video also points out that a manual transmission can be derived from the design. Pretty sure that the 991 manual transmission is from this. This should dispel the belief from some MT owners that they are immune from the woes that may befall a PDK transmission. Remember the guy who could not get the reverse light turn on in his manual transmission?
The first video also points out that a manual transmission can be derived from the design. Pretty sure that the 991 manual transmission is from this. This should dispel the belief from some MT owners that they are immune from the woes that may befall a PDK transmission. Remember the guy who could not get the reverse light turn on in his manual transmission?
That was me.... But in a manual we will not have issues with the solenoids in the valve body and any of the electronics related to shifting. Although my reverse lights died, the transmission still functioned mechanically.
The first video also points out that a manual transmission can be derived from the design. Pretty sure that the 991 manual transmission is from this. This should dispel the belief from some MT owners that they are immune from the woes that may befall a PDK transmission. Remember the guy who could not get the reverse light turn on in his manual transmission?
I believe, but I could be wrong, that the GT3 manual is derived from the PDK, but the 991 7 speed isn't.
garfunkle, very informative post, and seeking your expertise. I have 2017,C2, PDK 50k miles. While in park or at a stop I hear a rattle (like loose marbles or gravel) and I feel a slight stumble/vibration while seated. If I put it in sport or sport+ the rattle and stumble is reduced. I tried to pin point where the noise was coming from today. While in the cabin it sounds like its coming from the rear shelf on the drivers side. I checked for loose interior panels and did not find any. While outside of the car I had it on quickjacks and pulled off the body under-covers to look for where the sound was coming from. If I put my hand on the PDK I can feel the vibration coming from generally where the gear position sensor is located within the PDK. I can also hear the rattle emanating from this area. I changed the PDK fluid and pan along with the gear oil. The PDK fluid and gear oil looked and smelled generally good. The pan filter had no indication of any large fragments and the magnets had a slight build up of sludge. The car shifts and drives well. Is this noise and vibration normal? or should I be concerned. Very puzzling. Thanks for any insight you may have.
12-09-2019, 09:45 AM
PDK Repair + Heavy Duty Clutch
