6HP to 8HP conversion feasibility

[spyro235]

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.

[Cyrix2k]

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 :-/

[Cyrix2k]

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.

[Henn28]

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

[ard]

Originally Posted by Cyrix2k

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.

Holy shit.


Please tell us you wrote this up...


(Just kidding.)

A 5 year effort. Respect