8hp45 swap to 8hp50

bigshooter · 08-13-2023, 11:23 AM

I have an opportunity to buy a low mileage 8hp50 transmission from an LCI 340. I like the idea of replacing with the 8hp50 bc it holds +50nm more.

It should be plug n play, but I am planning on swapping the mechatronics to avoid having to clear the INS and to not lose my tune.

I’ve also read that the gear ratios are slightly higher in the 50 as compared to the 45.

1 - can I assume the mechatronics are identical between the 45 and the 50?

2 - will there be any issue with the difference in gear ratios? Will the tranny just “learn” and adapt to it?

Ideally I’d like to just pull the tranny, swap the mechatronics, install new trans, flush fluid, and be done.

Watsey · 08-13-2023, 04:50 PM

There seems to be some misunderstanding.

The mechatronic is the 'block' assembly inside the transmission consisting of a complex fluid pathway / various valves / solenoids.

The TCU (transmission control unit) is, in simple terms, a computer control unit for the transmssion. The TCU and the ECU operate in a continuous feedback loop. It is unlikely that the TCU from one transmission designation (i.e. 8hp45) would be compatible with a transmission with a different designation.

A transmission which contains physical gears, as opposed to a CVT, and cannot "learn" a new set of ratios. Each ratio is fixed and has been designed for the specific engine and the final drive for the specific vehicle.

The final drive for a 28d and a 40i are the same (2.81) BUT due to the very different rev range for the 28d/40i the transmission ratios will be very different.

In short, your proposed transmission swap isn't going to be viable.

bigshooter · 08-14-2023, 11:01 PM

It’s basically the same transmission. The 50 is the next evolution of the 45. It’s in the 2017-19 F3X series. The TCU is in the mechatronics to my knowledge, so by swapping the car would basically think the same transmission is installed. If I don’t swap the mechatronics, you have to go into ISTA to clear the INS

08-13-2023, 11:23 AM	#1
bigshooter Lieutenant 52 Rep 420 Posts Drives: 2014 328d xDrive Join Date: Sep 2019 Location: Northwest, CT iTrader: (0)	8hp45 swap to 8hp50 I have an opportunity to buy a low mileage 8hp50 transmission from an LCI 340. I like the idea of replacing with the 8hp50 bc it holds +50nm more. It should be plug n play, but I am planning on swapping the mechatronics to avoid having to clear the INS and to not lose my tune. I’ve also read that the gear ratios are slightly higher in the 50 as compared to the 45. 1 - can I assume the mechatronics are identical between the 45 and the 50? 2 - will there be any issue with the difference in gear ratios? Will the tranny just “learn” and adapt to it? Ideally I’d like to just pull the tranny, swap the mechatronics, install new trans, flush fluid, and be done.
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08-13-2023, 04:50 PM	#2
Watsey Major General 6414 Rep 8,498 Posts Drives: F31 330D sDrive M Sport Join Date: Jun 2015 Location: On sabbatical. iTrader: (1)	There seems to be some misunderstanding. The mechatronic is the 'block' assembly inside the transmission consisting of a complex fluid pathway / various valves / solenoids. The TCU (transmission control unit) is, in simple terms, a computer control unit for the transmssion. The TCU and the ECU operate in a continuous feedback loop. It is unlikely that the TCU from one transmission designation (i.e. 8hp45) would be compatible with a transmission with a different designation. A transmission which contains physical gears, as opposed to a CVT, and cannot "learn" a new set of ratios. Each ratio is fixed and has been designed for the specific engine and the final drive for the specific vehicle. The final drive for a 28d and a 40i are the same (2.81) BUT due to the very different rev range for the 28d/40i the transmission ratios will be very different. In short, your proposed transmission swap isn't going to be viable. __________________ Current : F31 330sD, remapped, Ohlins Road & Track, Millway camber plates, Quaife LSD, Stoptech brakes + Pagid RSL1 pads all round, Weichers front strut brace, Eibach front & rear anti-roll bars, Michelin MP4S.
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08-14-2023, 11:01 PM	#3
bigshooter Lieutenant 52 Rep 420 Posts Drives: 2014 328d xDrive Join Date: Sep 2019 Location: Northwest, CT iTrader: (0)	It’s basically the same transmission. The 50 is the next evolution of the 45. It’s in the 2017-19 F3X series. The TCU is in the mechatronics to my knowledge, so by swapping the car would basically think the same transmission is installed. If I don’t swap the mechatronics, you have to go into ISTA to clear the INS
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