6AT to DCT Converstion

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E60535i

New Member
Apr 27, 2019
4
xHP once mentioned the possibility of licensing his product out to 'pro tuners'. Understandably, over the past several quarters, his focus has been on casting a wide net — covering as many chassis and 6/8HP variants as possible, while adding a degree of customization — which makes business sense. He's better off making 97% of his target audience happy than spending his time on individual tunes and not meeting the needs of those who want anything from a basic update to different variations/personalizations of each of the tune stages. Perhaps, once the dust settles a bit, we'll have either pro tuners or even further command of the tune, with an additional module and corresponding license/fee. Either way, I've been in touch with him enough for him to know (and I'm sure others have also chimed in) that there are specific scenarios that cannot be accounted for with the customization module. However, these particulars make up a small percentage of all use cases — thus, understandably, pertinent solutions are currently on the back burner.

With regard to your torque reduction, although it seems counterintuitive, increased torque reduction can yield a faster shift time, in many cases. This, as it allows the clutch release of the off-going gear and clutch engagement of the on-coming gear to be less counteracted by input torque, facilitating shift completion within a tighter window and with less heat/wear. My sub-200 ms shift times have been the result of incrementally adjusting each shift to have a greater torque reduction. This, of course, can be overdone — thus, it's important to adjust and test (and allow full adaptation), incrementally. However, when dialed in (at least to the degree of precision that the customization module will furnish), you will likley not want for another transmission.

In terms of a weak point, I don't know that I have been exposed to a big enough sample size to be able to tell you with any authority. Some people have one thing fail, while many others have never experienced the same kind of failure and vice versa. My recommendation is to manage both overall torque levels, shock loads, and clutch slip at high torque loads (the last 2 the product of a combination of shift speed and shift torque reduction). For example, I don't doubt that a healthy and otherwise stock transmission can handle 700 WHP (even without PD clutches) — IF one manages the above areas. In terms of torque levels, rather than generating maximum torque as early as possible and then having to taper it off sharply with increased RPM and increasingly toward redline, I prefer to still reach peak torque early, but limiting it down low, to hold a flat torque level to redline. Generally speaking (with supporting hardware), this allows for a 'cooler' run to redline and allows for repeated runs with very consistent output (and encourages one to manage the ratios more appropriately). This, as you can imagine, is far easier on the power/drive train, without sacrificing peak power output (oftentimes making it more accessible more consistently).

Lastly, on the torque converter, with the Gen-2 6HP, aside from launching, the torque converter is essentially out of the picture. When driving off at a moderate pace in D, for example, the lock--up sometimes occurs at or below 1,000 RPM and remains locked until back at a near stop. When moderately driving off from a stop in 2nd gear, it allows a bit of RPM flair for additional torque, but transitions to a lock, once the target lock-up RPM begins to align with the TC RPM; and, thus is only open for a very short duration (and locks well before it shifts into 3rd). Otherwise, under hard launch in any mode (D/S/M), yes, the TCU will allow an initial torque-tapping flair until the TC and target TC-lock RPMs become more plausible — not too dissimilar from when one pre-loads the TC while staging a launch. Otherwise, there's virtually no scenario in which the TC handles the full engine load (and thus all of the torque). The TC is generally locked long before reaching peak torque, for example, and remains locked throughout the power band and even between shifts. I don't see a scenario in which a TC swap should be the focus of one's upgrades, between stock and ~750+ WTQ levels. And, even if one plans on reaching higher WHP levels (than the aforementioned torque levels), one can simply limit the torque output in either the TCU (with caps specific to gear) or DME (for overall caps or caps by gear and/or RPM) calibrations. Unless I was targeting 850+ WHP and wanted to make just as much torque as HP (with PD clutches and TCU calibration, of course), I wouldn't make the TC a concern. And, even then, it would only be a matter of tuning or tapering the launch appropriately.
 
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doublespaces

Administrator
Oct 18, 2016
7,483
AZ
I have a 'custom' xHP tune from @RayBan but this was before you could customize the shift points. In M mode, it is setup to autoshift but only at redline and it will hold the gear if the kick down is pressed, in addition to some shift point changes. I'm not sure if he does custom tunes anymore.
 

AJL

Private
May 11, 2017
29
Alright, so I'm in the middle of this swap and the shifter wiring is killing me. To get a clearer understanding of what needs to be for this, I made a diagram showing where to re-pin all the AT gear shift connectors to. Does anything stand out as being blatantly wrong here?

I used what info is out there already and newtis wiring diagrams to create it. Lines with arrow ends represent moving a pinned wire, circle ends are taps/splices.

EDIT: This is on an N55
 

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doublespaces

Administrator
Oct 18, 2016
7,483
AZ
Unless I missed it, I recommend providing the build date of your vehicle as well as chassis code. The swap details are different within models not to mention across years and chassis.
 

AJL

Private
May 11, 2017
29
Unless I missed it, I recommend providing the build date of your vehicle as well as chassis code. The swap details are different within models not to mention across years and chassis.
Ohh look at that, my signature isn't setup on this site :p Anyway, it's a 2011 e90 n55.

At this pointI'm honestly most concerned about where/how exactly to tap into the PT-CAN bus.

From my understanding, there shouldn't be any pinout differences between the e8x/9x chassis with the same engine/transmission/dme combos. At least so far as the shifter wiring is concerned. If so, that's news to me and a little concerning that I haven't realized that by this point in the project lol.
 

doublespaces

Administrator
Oct 18, 2016
7,483
AZ
Ohh look at that, my signature isn't setup on this site :p Anyway, it's a 2011 e90 n55.

At this pointI'm honestly most concerned about where/how exactly to tap into the PT-CAN bus.

From my understanding, there shouldn't be any pinout differences between the e8x/9x chassis with the same engine/transmission/dme combos. At least so far as the shifter wiring is concerned. If so, that's news to me and a little concerning that I haven't realized that by this point in the project lol.
If you just look at the 135i transmission harness and compare it to the 335i harness you'll see there is a pretty large difference. Also some wiring is different if you are pre or post 09. I've seen two post 09 DCT transmission harnesses and the pins are different inside the pig tail. I would need to sit down and study my own notes and compare them to what you've posted, to be sure we are talking about the same things, but to some degree, there are wiring differences for sure.

As for PT-CAN, I don't think it matters. I was simply going to tap the wires from the FRM I think that way I can avoid going through the firewall for anything.
 
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AJL

Private
May 11, 2017
29
If you just look at the 135i transmission harness and compare it to the 335i harness you'll see there is a pretty large difference. Also some wiring is different if you are pre or post 09. I've seen two post 09 DCT transmission harnesses and the pins are different inside the pig tail. I would need to sit down and study my own notes and compare them to what you've posted, to be sure we are talking about the same things, but to some degree, there are wiring differences for sure.

As for PT-CAN, I don't think it matters. I was simply going to tap the wires from the FRM I think that way I can avoid going through the firewall for anything.
Wait I just realized - are you talking about the harness in the engine bay? If so, yes that's clearly different. I bought one from a 135i N55 to replace my current AT one. Comparing that to the equivalent harness for a 335i w/ DCT it's the same (according to newtis). It's fits exactly the same too!

Anyway, I just ended up using posi-taps for the PT-CAN and 15WUP (Green/red) signals at X14271. Connections seem strong, so it should be fine. Now just to find that engine harness ground bolt I dropped. :coldsweat: It just vanished, you know how dropped bolts do. Once I take care of that, it's time to either flash all the modules or find out where I screwed up lol.
 

NoQuarter

Captain
Nov 24, 2017
1,063
Indiana
Wait I just realized - are you talking about the harness in the engine bay? If so, yes that's clearly different. I bought one from a 135i N55 to replace my current AT one. Comparing that to the equivalent harness for a 335i w/ DCT it's the same (according to newtis). It's fits exactly the same too!

Anyway, I just ended up using posi-taps for the PT-CAN and 15WUP (Green/red) signals at X14271. Connections seem strong, so it should be fine. Now just to find that engine harness ground bolt I dropped. :coldsweat: It just vanished, you know how dropped bolts do. Once I take care of that, it's time to either flash all the modules or find out where I screwed up lol.
Be sure to use twisted pair cable for the PT-can connection and keep the twists all the way up to the connection.
 

AJL

Private
May 11, 2017
29
Just an update on the swap - I've got everything wired up and confirmed with ISTA that both the DKG and GWS are communicating correctly with the vehicle. Was able to update the VO and read/write to the GWS without issue using NCSExpert.

Unfortunately, the auto driveshaft (p/n 26107614396) does not seem to fit due to moving from a small diff housing to the large one. The center support bolt holes don't line up, because the back half of the driveshaft is too long. Didn't get an exact measurement yet, but it looks to be about 20mm. According to a thread posted earlier (post #11), I thought this would work. Unless that was only referring to pre-2007 models that used p/n 26107614433.

Either way, it's not a huge deal. A used driveshaft can be had for like $100, or I can have my current one shortened a bit if need be. I'm more concerned about just getting the transmission filled and making sure it goes into gear at this point lol.

27246
 
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AJL

Private
May 11, 2017
29
New (to me) driveshaft 26107614433 is here and fits like a glove. Already got the tranny filled and confirmed it goes into gear. I think there may be a problem with the sport button, but haven't really gotten to test it. Should have everything buttoned up and at least drive-able tonight.
Can't wait to take it out for a drive :eek:
 

doublespaces

Administrator
Oct 18, 2016
7,483
AZ
Just an update on the swap - I've got everything wired up and confirmed with ISTA that both the DKG and GWS are communicating correctly with the vehicle. Was able to update the VO and read/write to the GWS without issue using NCSExpert.

Unfortunately, the auto driveshaft (p/n 26107614396) does not seem to fit due to moving from a small diff housing to the large one. The center support bolt holes don't line up, because the back half of the driveshaft is too long. Didn't get an exact measurement yet, but it looks to be about 20mm. According to a thread posted earlier (post #11), I thought this would work. Unless that was only referring to pre-2007 models that used p/n 26107614433.

Either way, it's not a huge deal. A used driveshaft can be had for like $100, or I can have my current one shortened a bit if need be. I'm more concerned about just getting the transmission filled and making sure it goes into gear at this point lol.
Are you referring to this thread?

https://bmw.spoolstreet.com/threads/swap-188mm-auto-pumpkin-for-215mm-diff-cover-options.1561/

The back half of the driveshaft is telescopic, so it should slide inward, no?
 

AJL

Private
May 11, 2017
29
Are you referring to this thread?

https://bmw.spoolstreet.com/threads/swap-188mm-auto-pumpkin-for-215mm-diff-cover-options.1561/

The back half of the driveshaft is telescopic, so it should slide inward, no?
Yes, that one

The slip joint is on transmission side of the center bearing, so the back shaft being too long can't be compensated for.
27371



Also, do you happen to know anyone who has done the programming for this swap before? I thought I had it correct, but I'm getting this weird code on the DME:
3BDD - No Message (request torque electronic transmission control, 0xB5), receiver DME, transmitter TCU/HIM.

And the transmission won't shift past second since that throws it into a failsafe mode :(

I can communicate with both the DKG and GWS, so I *assume* the wiring isn't the problem and that its some kind of programming issue. Just don't know where to start. I suspect the transmission is the issue and not the DME though.
 

AJL

Private
May 11, 2017
29
Well I was able to resolve the 3BDD error message quite easily actually, thanks to some advise from BimmerGeeks. I just needed to reset all engine adaptations using INPA.

So the car is now running and driving error free!

I still need to put my interior together, figure out what rattles are due to my hasty re-assembly, and fix what sounds to be a massive exhaust leak, but I'd say the swap itself is complete.
 
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m_a_itani

Lurker
Mar 18, 2019
11
Hey guys,

last weekend I did the wiring for my dct swap. Iam a little bit confused because my old X6021, X6031, X6041 female connectors that came from the transmission has 2 rows with 4 big Pins. So my original male connector has it, too. The new connectors of the dct wire have 1 row 4 big Pins and one row with 8 small Pins like the wiring diagram.

Can anybody tell me if that is normal?View attachment 22829
Hello did you make the swap? And what automatic transmission fitted to the car 6hp19 or 6hp21?
 
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