Menu toggle

GT4 Gearbox Failure

geoff.private@underwood.co.uk

geoff.private@underwood.co.uk

New member
I have a GT4 with 3k miles and it suddenly dropped out of Third Gear. A google search shows on Rennlist that this has happened to others and that the whole transmission has to be replaced. I am told by my Porsche Centre that there aren't any available and Porsche will have to make one. Sounds to me that several others have failed??
 
So it seems not just GT4 but GTS tracked cars too, I can't imagine that the 981S is exempt from such failures since the 3.4 engine and transmission in the GTS is the same as the S although there may be some minor differences and some do get tracked, anyone know more on this?

 
I can check the PET files when I get home but in PDK they have same torque capacity 2.7L through 3.8L Clubsport, which I understand via ZF source to actually be 500Nm. I would suspect the same (same gearbox) is true of manual box although maybe the dry clutch might have more plates?

The thoughts in the USA was a bad batch of welding of 3rd gear so it might be affecting cars built during a particular period but not necessarily a particular VIN range.

There have been a couple of 3.4L cars affected but these were on track but the relatively few 3.8L cars affected had road only or road and track use.

 
Sorry to hear that Geoff but, as said, not an unknown occurrence for tracked cars.

I believe that Porsche won't let the PCs strip the gearbox to identify the cause of the problem, so it's just a straight transaxle swap. I'm very surprised that a new transaxle isn't ex-stock since I was under the impression that the GT4 uses the same transmission as that used in the 981 S/GTS.

By the way Ralph, the G81/20 transmission in the GT4 has a torque capacity of 420Nm and uses a single-plate dry clutch with a peak torque limiter incorporated in the clutch slave cylinder. The only other notable difference is that the GT4 has a lighter DMF than its siblings.

Jeff

 
All gone to the USA!

I assume therefore they will replace soonest. It must be frustrating to say the least.

 
Motorhead said:
Sorry to hear that Geoff but, as said, not an unknown occurrence for tracked cars.

I believe that Porsche won't let the PCs strip the gearbox to identify the cause of the problem, so it's just a straight transaxle swap. I'm very surprised that a new transaxle isn't ex-stock since I was under the impression that the GT4 uses the same transmission as that used in the 981 S/GTS.

By the way Ralph, the G81/20 transmission in the GT4 has a torque capacity of 420Nm and uses a single-plate dry clutch with a peak torque limiter incorporated in the clutch slave cylinder. The only other notable difference is that the GT4 has a lighter DMF than its siblings.

Jeff
Click to expand...

Jeff,

Accepting I'm off OP's topic but as this a potentially related aspect...

The PET files show:

GT4 Gearbox type G81.20 I220 981.300.020.22, or 981.300.020.BX

981 Cooking Gearbox type G81.20 I220 981.300.020.21, or 981.300.020.AX

So the same as you said except for minor fit differences indicated by .21 v .22 and AX v BX.

About torque in PDK gearboxes, when I was having my engine tuned I said I didn't want more than 420Nm as all 991.1 engines including GT3 (in 2015) were 420Nm maximum torque. The ZF site had 420Nm. But later, thinking about it some more, why would an OEM like Porsche run cars to the maximum torque capacity of the gearbox?

This is why I believe the ZF engineer who said privately that the PDK will take 500Nm and I expect the 420Nm you mention for the manual is an OEM engine level, not the gearbox's limit.

It is the same with 991 turbos, these are being tuned by Techart, for example to give 130Nm more and are running standard transmissions. There is a limit somewhere but Techart are not a flaky outfit although 880Nm is a lot to handle.

Ralph

 
Thanks for the confirmation Ralph. And I'm sure you're right concerning torque capacity - for durability, Porsche wouldn't run the gearbox anywhere near it's limit.

Accepting that transmission failures are relatively rare these days, like Geoff I'm very surprised that replacements aren't available off-the-shelf. Either someone in the parts department needs to have their backside kicked or, playing devil's advocate, maybe the fact that no transmissions are available is indicative of the fact that Porsche/Getrag haven't got to the root cause of the problem?

Of course, as Ralph has pointed out, perhaps they've all been shipped to the USA.....for fear of litigation?

Jeff

 
what month and year is the OP failed car, in the USA none have broken on early cars yet, ie before Oct 2015 again, odd and points to a bad batch.

 
420Nm engine output to 500Nm transmission capability is a reasonable safety margin and so design faults are very unlikely so many earlier versions are in use, I'd be amazed if in the timescale from these failures being announced in the states to now if the transmissions hadn't been stripped and analysed, I agree with Chris that a repaired rather than replaced unit should be available but this may be due to warranty issues.

It appears from many of the reports that the failure seems to be failure of the gear location on the shaft or similar one or two part failure, gearboxes are not usually that difficult to repair and yet we hear that rather than repair a PDK it is Porsche practice to fit a new replacement and now we are seeing it on the manual transmissions too, if they are doing this on the GT4 and GTS then it rolls on across the range as it is much the same transaxle.

OPC's do strip and at least part rebuild engines, no doubt Porsche would want to keep repairs within their own control including OEM parts supply but others are capable and I would expect ZF would have some repair facility available, Porsche Approved hopefully.

If parts are in the PET as Ralph says then they should be available at least through Porsche but I doubt if Porsche will state what the problem has been or if they think that all which may be suspect have all been tended too. I hope they get their act together on this soon!

 
It is the rise of the ORU, the Optimal Replaceable Unit which we had emerge in the 1980s in computers. No longer did we have the engineer with analysis tools and a soldering iron but service 'technicians' who swapped circuit boards until they found the errant component.

So it is with cars, on factory tours I always ask "is the car is designed for manufacture or servicing?"

I am surprised manual gearboxes are replaced but in a world of increasing product complexity and integration it is perhaps understandable. I would guess Porsche just return faulty units to Getrag under their warranty arrangement and get a replacement in return, as any OEM would with a first tier supplier.

 
with the GT3 engine a lot were sent back out with a fix, gear boxes maybe stripped and reused.

 
True Ralph but there must be an alternative to outright unit replacement, the most difficult part of the PDK is the operating system with it's internal sensors etc and the fact that it needs the use of a PIWIS to carry out the oil flush and oil change of that part of the unit. The gearbox itself is mainly in common with the seven speed boxes as used in the 991 and at some point the OEM will decide not to support the existing models as they move on. Maybe someone is setting up for a second line repair and if so maybe upgrading of existing units to take more torque and BHP.

 
You must log in or register to reply here.

Posts made and opinions expressed are those of the individual forum members

Use of the Forum is subject to the Terms and Conditions

Disclaimer

The opinions expressed on this site are not necessarily those of the Club, who shall have no liability in respect of them or the accuracy of the content. The Club assumes no responsibility for any effects arising from errors or omissions.

Porsche Club Great Britain gives no warranties, guarantees or assurances and makes no representations or recommendations regarding any goods or services advertised on this site. It is the responsibility of visitors to satisfy themselves that goods and/or services supplied by any advertiser are bona fide and in no instance can the Porsche Club Great Britain be held responsible.

When responding to advertisements please ensure that you satisfy yourself of any applicable call charges on numbers not prefixed by usual "landline" STD Codes. Information can be obtained from the operator or the white pages. Before giving out ANY information regarding cars, or any other items for sale, please satisfy yourself that any potential purchaser is bona fide.

Directors of the Board of Porsche Club GB, Club Office Staff, Register Secretaries and Regional Organisers are often requested by Club members to provide information on matters connected with their cars and other matters referred to in the Club Rules. Such information, advice and assistance provided by such persons is given in good faith and is based on the personal experience and knowledge of the individual concerned.

Neither Porsche Club GB, nor any of the aforementioned, shall be under any liability in respect of any such information, advice or assistance given to members. Members are advised to consult qualified specialists for information, advice and assistance on matters connected with their cars at all times.

Porsche
Lockton
Pirelli
Officially approved
Oracle Finance
WEX Esso
Collecting Cars
Archant Dialogue
Back
Top