The so-called slushbox is a far cry from what it used to be. Nowadays it looks as if ZF is making huge waves with its superb torque convertor autos. I like torque convertor autos I much prefer them in vehicles that have to deal with a broader range of daily use and varying conditions. It was exactly for this reason that I was pleased with the fitment of a more robust, reliable, tolerant and smoother 8-speed auto in the Cayenne rather than an iffy, launch mode drawcard DCT box. The problem with DCT boxes as described in this thread is that they're dependant on software logic to second-guess the driver's intentions and pre-select a gear accordingly. The better the software logic, the quicker reacting the transmission. Porsche seems to have gotten their DCTs better calibrated than say, BMW.

A key issue with a torque convertor transmission in the performance saloon segment is that they don't offer a true launch control mode like can be had with a DCT. It's these launch control programs that are putting down the on-paper bragging rights to amazing 0-100 km/h acceleration times. It's these on-paper times that consumer buy on, unfortunately. Personally, I could care less for launch control. It's a novelty and one that should be used as seldomly as possible, in my opinion, in the interests of mechanical sympathy.

Ultimately it's all about application or, shall we say, fit-for-purpose. A planetary gear, torque convertor transmission does marginally isolate the driver from the drivetrain compared with the immediacy and connected-in feeling of a constant mesh gearbox - be it manual, sequential or dual clutch. So in an M3 or, to be absolutely extreme, a 458 Italia, a DCT is a far more appropriate option. But in a two-ton family saloon that happens to be mega fast? I can see no reason why anyone buying an F10 M5 wouldn't forego launch control for the smoother, broader range of talents of a modern torque convertor auto.

Well what’s all this brouhaha over the next M5′s transmission choices. A little logic may help in understanding what the possibilities will be. Let’s start with what we know and what we’re willing to bet the farm on.

1. The engine in the next M5 is the S63B44 capable of producing 530 lb-ft of torque (approximately 717 Nm).

2. BMW will work with their current vendor pool to source the transmission.

3. BMW is conservative and the torque handling capabilities of the transmission will exceed the flywheel torque of the engine by a healthy margin.

We’re more than sure that the S63B44 will be the engine in the next M5. It’s received great critical acclaim in the X5M and X6M models. It also produces a ton of torque from fairly low RPMs through fairly high RPMs. More like a torque plateau than a torque peak.

BMW currently works with ZF and Getrag to supply gearboxes. Both can supply manuals, automatics and dual-clutch transmissions. But the subset of their transmissions that can provide the torque handling BMW would prefer is fairly small.

So, currently the X5 and X6 Ms use the ZF 6HP32 which can handle 1000 Nm of torque. That’ll give us what BMW considers to be the minimum torque handling capacity they’re willing to live with. And yes, the 6HP32 would plug right into the new M5.

ZF’s six speed in the 135i, 335is, and the M3 can handle peek torque of around 600 Nm. So the manual is out. Does anybody make a manual that can handle the ‘awesome’ torque of a BMW turbo engine? Well sure, that and more actually – Tremec makes a really great 6 speed manual and has introduced an enhanced torque handling capacity box called the Tremec T56 Magnum. It’s one stout gearbox. Tremecs are used in ‘vettes and while they can feel balky at slow speeds and light loads they come alive under power. Good gearboxes, but as far as we know BMW doesn’t use Tremec as a supplier. You could also go a little nuts and get a 5 speed Jerico gearbox, but that’s too NASCAR for any German car company.

But there are alternatives. Getrag makes a 7DCL750 dual-clutch that handles 750 Nm. Scratch that one off the list. ZF makes the 7 DCT 50 which can handle a peek of 1000 Nm. Oh, keep that one one the list. ZF also makes the 8HP which we believe can handle a peek of 1000 Nm.

But that’s an automatic right? Well it can be. But the torque converter can be swapped for a automated clutch. OK – so an 8 speed DCT! Not so fast, we don’t know if the automated clutch assembly for the 8HP changes the torque handling capacity. But, in a bet the farm move (I know longer own the farm), I suspect it’ll be an 8HP that ends up in the M5.

Why?

Because of what the two additional overdrive ratios do for EfficientDynamics.

References

GETRAG Powershift® 7DCL750 TRANSMISSION GETRAG Corporate Group - 7DCL750 TRANSMISSION
ZF 8HP ZF Friedrichshafen AG | 8-speed-automatic transmission

ZF 6HP32 ZF Friedrichshafen AG | Product Overview | Cars Multi-ratio automatic transmissions

ZF 7DC50 http://www.zf.com/zfXmlServlet sessionAttribute=xmlRoot&languageISOCode=EN&result Url=/corporate/en/products/product_overview/ProductContentPage.jsp&serviceUrl=http://appsprod01.zf.com/zf.productDataBase/service//applicationLayerSelect&applicationGroupID=&divisio nShortcut=&applicationID=12288&businessUnitShortcu t=&productFormID=12162&productGroupID=12147&produc tTypeID=316999&productTechnicID=12141

Tremec T56 TTC: TREMEC Transmissions

Jerico Jerico Performance