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Originally Posted by Lubehead
BMW does not manufacture the transmission, ZF does. I do not believe BMW has "motive" other than to provide the highest level of technology available with regard to most major components of the vehicle especially the drivetrain. ZF engineers have evidently come to the conclusion that their product (and their good name) is well served by the recommendations they have published.
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What does "well served" actually mean?
Do you mean that ZF believes the longest service life will be achieved by not ever changing the fluid?
Or has this become a calculus of 'ownership costs' and 'owner hassle' and 'likelihood of trade in' combined with odds of failure to determine this is 'best'?
(Much like the way a recent panel of womens health experts determined that mammograms are not recommneded for women under 50, since the false positives are worrisome, and cause more biopsies- even if it does save lives?)
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JCL's reference to the transmission as hydraulic system is spot on. And his message regarding its comparison to an engine is relevant and factual.
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I do agree. There are wear components in a tranny though, so it isn't JUST hydraulic... and admittedly engines are hotter, fuel shear more of an issue as is contamination via combustion products. But my argument was that you rarely hear of "oil falure" as a cause of engine failure- would this lead one to believe oil doesn't need to be changed? It was an argument taken to abstraction.
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In industrial applications many OEM's continue to recommend drain intervals that are not relevant to today's superior performance fluids and most certainly do not pay attention to the reliability engineer's focus (and industries movement towards) condition based fluid change intervals as opposed to time or mileage based oil change intervals.
BMW/ ZF are I am sure, cognizant of the characteristics of the fluid as well as the dynamics of the wear mechanisms occurring in the transmission itself. In hydraulic systems especially, it is well known that particulates in the fluid damage system components and yet there are plenty of maintenance personnel who believe they are doing good by the machines they are responsible for by changing oil because it has achieved a certain length of service time, when in fact the opportunity to do more damage as JCL suggests, is real and in fact counterproductive to the machines life. Heavy equipment OEM's are well aware of this and ZF is a vendor to that market as well.
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I'd like to think ZF & BMW have ONLY the longevity of the AT assembly as their sole determinant as to the fluid service. Until that is confirmed, I thin the community is ill served by broad assertions that 'high tech' fluids will save the day.
I can find NO DATA that says regular preventative maintenance will damage transmissions. Plenty of data that neglected transmissions are ill served by late services and flushes. I'd like to separate these two concepts.
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As far as the BMW/ZF transmission itself, the only improvement I would like to see would be an oil sampling valve somewhere on the transmission or its cooler lines. This valve (which would cost no more than $10.00) would enable monitoring of the fluid without opening the unit to the atmosphere. They are commonly installed on heavy equipment hydraulic systems, transmissions and many industrial hydraulic systems. Fluid degradation, contamination, viscosity, etc could easily be monitored and action could be taken as analysis results dictate.
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Personally I suppose I agree, but I need to ask you "why?" Isn't the BMW interval of 100,000 miles satisfactory?
