6HP to 8HP conversion feasibility
 

Has anyone looked into if swapping an 8 speed transmission into the earlier E70s is feasible? I'm doing some preliminary research using my 4.8 as a reference and a 50i as the donor. So far, the bellhousing bolt pattern appears to be the same. I'm guessing overall length is close as well - the rear driveshaft is 1mm different in overall length, but of course that incorporates the transfer case as well. The E70 has seen a number of transfer cases over the years and it's another challenge to address - is the bolt pattern and splined output shaft the same between the 6HP and 8HP? If not, then the transfer case that goes to the transmission would have to be used and I'm not sure how that would integrate. From what I can tell, it does look the same (at least the bolt pattern). Once the mechanicals are addressed, we need to worry about the electronics. I've heard, though not confirmed, that the 8HP uses FlexRay for communication whereas the 6HP uses CAN bus. My suspicion is that while this might be true on F-series vehicles, the E70 likely retained CAN bus for its 8HP implementation. Assuming the message format is the same, I suspect the transmission may be plug and play... As far the immobilizer is concerned, I have the equipment to synchronize the ISN on both the 6HP & 8HP. It looks like the CAS is shared between 6HP & 8HP, so I again suspect it can be made to work. Any thoughts? Does anyone have wiring diagrams for the 8HP by any chance?

Wiring diagrams are available here. https://www.newtis.info/tisv2/a/en/

The 8 speed transmission uses a different transfer case than the 6 speed. I checked out some ebay photos and the output of the 6 vs 8 speed does not look the same. The best way to do this may be a complete donor vehicle so you can get trans, tc, driveshafts, diffs and mounts. I would love to have the 8 speed in my diesel. E70 LCI diesel in Europe has it.

Interesting. I did not know that.

Thanks. According to that, both use CAN bus and appear to be wired about the same. There's a couple pin differences and an additional connection on the 8HP for tiptronic (I think). None of that seems particularly worrisome.

At least on the V8, the transfer case bolt pattern does look the same to me? See these two auctions
https://www.ebay.com/itm/2007-2010-B...cAAOSwEFhdpLeq

https://www.ebay.com/itm/2011-2013-B...8AAOSwz~RdI3SR

On the plus side, I can reference a 2013 xDrive35i. I'd like to keep the swap as simple as possible so if the original transfer case can bolt on and the original driveshafts can be reused, that would be fantastic. If I ask really nicely, I might be able to get a CAN bus capture from the 2013 which would definitively answer if the messaging is the same.

To me, it looks like the output shaft is longer on the 8 speed.

You're right. I think the ATC450 could also be swapped in or it looks like it may be possible to put a spacer between the 8HP and the ATC700. In the pictures, the ATC700 has an almost flush mounting flange whereas the ATC450 is recessed. I also did some more research and found the diffs are different. Early models received very short gears - 4.44 in the gas 3.0 and 3.91 in the 4.8. Later models received 3.15s which works with the broader torque curve of the turbo engines & the wider ratio spread of the 8HP. While the 8th gear is about comparable to 6th in the 6HP, first gear is much shorter on the 8HP. I think I'd prefer to try and keep the 3.91s if possible.

I also looked up the immobilizer and it looks like the CAS3 was used for the entire production run of the E70. That means it should absolutely work with the 8HP.

Very interested in how this goes. I know the ATC700 is thought to be much stronger- and my 35d would need it. I've looked into swapping to the 3.15 of the 50i, to bring my final drive down from 3.64, to increase fuel efficiency, run at lower RPM, and generally run quieter/ more efficiently on the long haul. If you were to swap the 8 speed, I'd be very curious to see a what it takes!

Regarding the rear difs, the 3.15 for the 5.0 has a different part number than the 3.15 for the 3.0. This may be due to the larger axle shafts on the 5.0. Some of us diesel people are considering a 3.15 dif swap to get better highway MPG. A 3.15 dif alone will lower the highway RPM 50% compared to the 8 speed/3.15.

Where are you getting the 50% number from? By my math, it’ll lower our highway rpm by 15.5% from our 6 speed/3.15. I was under the impression that that would put us very in line with the engine speed of the f15/ 8 speed.

Sorry for the confusion on the 50% number. I was using a final drive calculator on some website a while ago. If I remember correctly, my current 2600 rpm at 80 mph would go to 2300 with the 3.15 dif. Then 2000 with the 8 speed.

Yea, that matches my math- but at 15.5% change it would Be more like down to 2200 from 2600.

I believe I’d be content with the 50i diffs alone- I use my x5 for a decent amount of long distance maxed it towing. The 3.15 diff would bring my 6th gear to a much lower cruising and would make my “new” 5th gear about 5% shorter than my current 6th. I wager I’d be cruising a lot of the time in 5th while hauling long distance, but I’m not worried about that. Basically an equivalent situation regardless.

I have some bad news. It looks like the tool I have is not capable of resetting the 8HP EGS on the E70; it only works for F series vehicles. In fact, it sounds like there are no tools that can reset the E70 8HP EGS... so at this point, either the 8HP needs to come with the associated CAS or I would need an entire donor vehicle to proceed :-/

Update on this - the ISN can now be reset on these and I'm happy to report that I successfully swapped in an 8HP70 from an E70 50i. Many of the earlier comments were correct. The old transfer case does not fit as the 8HP70 output shaft is longer. The ATC700 from the X5M will physically fit the transmission but is too long for the driveshaft. The ATC450 from the 50i is slightly shorter and works with the factory driveshaft, barely, however it requires wiring changes. In fact, the entire transmission + transfer case assembly is longer than factory as the N63 must mount the transmission further forward. This means the crossmember must be modified and the front driveshaft doesn't fit either. The F25 X3 front driveshaft is the correct length and splines into the ATC450, but the bolt circle on the front u-joint is smaller than the E70 so a solution is needed for that. Another big issue is the bolt pattern for an N63 is different than an N62, so the transmission needs modification for it to fit. The N63 does bolt on and works with the N62 starter. Otherwise the transmission works fine with the exception of a couple fault codes that don't set a CEL. I'm working on resolving those now, one of the codes is for the door status that can be resolved by fitting the later FRM and JBBE.

Damn, great work! I dream of an 8HP in my pre LCI E53. Such a great gearbox.

Holy shit. :bow: :bow: :bow: :bow:


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