6 speed vs 8 speed auto box

[msm]

Came across some interesting opinions on some of the US forums with regards to automatic gearboxes.

Apparently, the new 8 speed can't handle as much torque as the older 6 speed boxes. Hence, the X5M and X6M still retained the "old" 6 speed box while the rest of the less powerful engine derivatives got the updated 8 speed boxes. I can't seem to find info on BMW SA's website to confirm what boxes local cars have.

There was mention on this forum that the new 8 speed boxes could handle more torque but this seems to prove otherwise ...

Anyone care to shed some light.

 

[Raybimmer]

The 6 speed box may better suit the M models ammount of torque .
The more gears you have the more gear changes occur in the lifetime of the box , how do they match for lifetime ?

 

[ntuthuko]

Could you please post the link msm,if thats ok with the mods.Sounds like an interesting read

 

[msm]

Could you please post the link msm,if thats ok with the mods.Sounds like an interesting read

Not really an article, but as I mentioned some opinions on the forums. Here's one of the random links:

I remember reading a review that they kept the 6 speed transmission the same because the transmission was originally used from 7 series V12 because of the torque rating.

I read in the Car Mag "BMW" about the X6M (same power train as X5M) that the reason why those cars have still the 6 speed, and not the 8 speed is because the 6 speed can deal with the extra torque.

Source of above quotes

These are just opinions of course, but some of the arguments make sense, hence my initial question.

 

[P1000]

8 Speed ZF is available in a 900Nm version for petrol, the same box has a 1000Nm rating for diesel (the six speed was only rated up to 750Nm). The technology is MUCH more advanced than the six speed.

http://en.wikipedia.org/wiki/ZF_8HP_transmission
http://www.zf.com/corporate/en/prod...atic_transmissions/8hp_automatic_transmission. <=click on the pdf under "further information"

 

[msm]

8 Speed ZF is available in a 900Nm version for petrol, the same box has a 1000Nm rating for diesel. The technology is MUCH more advanced than the six speed.

That's what I thought too, but just wondering why they did not put it in the X5M/X6M if it was so good.

 

[P1000]

8 Speed ZF is available in a 900Nm version for petrol, the same box has a 1000Nm rating for diesel. The technology is MUCH more advanced than the six speed.

That's what I thought too, but just wondering why they did not put it in the X5M/X6M if it was so good.

It has more likely to do with availability at the time of deevelopment/launch of the XxMs, if I had to guess.

 

[Bayn46]

The F10 M5 is using a 6 or 7 speed DCT box, if I recall correctly. The 8 speed DCT box seems to have only been released recently along with the M-sport packages. Might explain why the new M's don't have the 8 speed.

 

[XMAX]

DANG... thats some awesome torque ratings...

I can imagine the tuning capabilities with these cars...

 

[Smartiesman]

The new F30 330d comes out with a 8 speed box

 

[P1000]

The new F30 330d comes out with a 8 speed box

Yes, it has the 8HP70 - good for "only" 700Nm both petrol and diesel...

 

[moranor@axis]

you probably find the 6 vs 8 speed debate is just people not trusting new tec... i dont really see what you cant make a strong gearbox with more gears it just gets heavier and bigger thats all...

seems to me using the gearbox is a good way to limit the performance on boosted cars :rollsmile:

 

[P1000]

you probably find the 6 vs 8 speed debate is just people not trusting new tec... i dont really see what you cant make a strong gearbox with more gears it just gets heavier and bigger thats all...

seems to me using the gearbox is a good way to limit the performance on boosted cars :rollsmile:

You did not read the PDF, did you?

The 8 speed is much lighter than the six speed, despite handling more torque. The 6 speed box was okay, the technical update versions were fantastic (a huge improvement, but IIRC none of them were fitted to BMWs), but the 8 speed is a technical masterpiece compared to the rest.

 

[moranor@axis]

you probably find the 6 vs 8 speed debate is just people not trusting new tec... i dont really see what you cant make a strong gearbox with more gears it just gets heavier and bigger thats all...

seems to me using the gearbox is a good way to limit the performance on boosted cars :rollsmile:

You did not read the PDF, did you?

The 8 speed is much lighter than the six speed, despite handling more torque. The 6 speed box was okay, the technical update versions were fantastic (a huge improvement, but IIRC none of them were fitted to BMWs), but the 8 speed is a technical masterpiece compared to the rest.

nope did not read it but logic tells me you can make a strong 8 speed because having more gears does not make a box weaker... im going to read it now because it sounds very interesting...

 

[moranor@axis]

P1000 link does not take you to pdf i get an 'error 404' where do i find the pdf on the site?

 

[P1000]

P1000 link does not take you to pdf i get an 'error 404' where do i find the pdf on the site?

very strange! The google link takes me to that url, but entering it manually does not work, so here is the google link:

http://www.google.com/url?sa=t&rct=...sg=AFQjCNECMcWt1icUjKgwuO4Y1lolcwRggA&cad=rja

and here is the direct PDF link, although it might also not work:
http://www.zf.com/media/media/img_1...tion/8hp/www_11_023884zfge_8HP_Produkt_EN.PDF

EDIT: okay, the pdf works, but the zf site seems to be wonky, google "zf.com 8 speed" first link that is not an add should work.

 

[msm]

Ok, here's a snapshop from the doc:

According to realoem, both my 2007 330d and X5 have the 6HP26Z, which is an update on the 6HP26, so I'm not sure where it falls in terms of specs on the diagram .... (Just out of interest, this is the same box as the X5M)

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Now here's a can of worms: The F30 335i has a 8HP45Z gearbox. Once again not listed, but using the ones listed this box might not be able to handle the same torque as the previous 6 speed E90 330d box (6HP26Z).

So yes, while the 8 speed might be superior and in certain models be able to handle more, it looks like the F30 gearbox variants might not be a strong as the E90 330d boxes.

---

@P1000: Do you have any info on the 6HP26Z. Can't find exact torque figures on that one.

 

[P1000]

I don't think the Z means anything apart from it is a ZF box. The 6hp28 was the update on the 6hp26, the 21 on the 19 and the 32 and 34 were new. So BMW did not get the updated boxes as I said in a previous post. Also, IIRC the E90 335 got the 6hp19 box, which has rated at 350Nm, where the *hp45 is rated for 450Nm.

 

[msm]

Also, IIRC the E90 335 got the 6hp19 box, which has rated at 350Nm,

Correct, according to realoem.That is rather interesting that the E90 335i got such a "weak" box and guys are modding the sh!t out of those things.

Doing some random browsing and it seems that only the E90 330d/335d received the higher spec boxes (6hp26) while the rest of the range including the 335i received the 6hp19