I agree with DKL that it tends to be the nature of the beast, and it isn't solely a BMW issue. Automatic transmissions have been made more complicated in recent years, primarily with the inclusion of more electronics, and additional gears. A six speed automatic just has more inside of it than a three speed automatic. More parts means more things to fail. To the extent that those parts are sensors and so on, look to the experience of BMW and BMW owners with various electronic components in the rest of the vehicle (window regulators, MID display pixels, heated seats, tail light sockets, ignition switches, etc). Now think about what happens when similar electronic components are used inside the transmission to control shifting. BMW puts the control package in there. It is not hard to predict the outcome.


Other factors that could play a part, aside from the basic transmission components such as gears and clutch packs, and which are common to the two models, are:

• Specifying a transmission that can't handle the power (doesn't appear to be a problem, since the failures aren't generally heat-related)
• Transmission cooling system (doesn't appear to be an issue)
• Changing the fluid (quite a few reported failures are due to changing the fluid against BMW recommendations, either due to improper fluid, losing the viscosity of the aged fluid which was preserving the transmission, or disturbing the sediment in the valve body)
• Abusive driving practices (always possible, if there are any boy racer types driving these vehicles, lol)
• Manual shifting using the Steptronic feature. This shouldn't be a problem, as the vehicle will save you somewhat from improper shifting, but simply increasing the number of shifts will shorten the life. A good predictor of transmission life is number of shifts, which is why highway miles are easier than stop and go traffic use. Manually downshifting at every light or stopsign (which the vehicle will avoid, if left to itself) does add wear to the transmissions. Hard to say how much.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue