Thoughts on Changing Transmission Fluid

[Brandon002]

So what we got out of all this back and forth banter, is that it's a matter of personal preference and what gives you peace of mind.

[JCL]

Originally Posted by bcredliner

Would you post the source of the adaption capabilities?

I don't have the ZF document handy (would have to search for it) but it is part of the Electronic Transmission Control (ETC). The following is from a BMW document dated 2003:

Transmission Features and Principles of Operation

Adaptive Hydraulic Pressure Control

Pressure adaptation has been a feature of ZF automatic transmissions since the 4HP22EH. The TCM will maximize shift quality by adapting to transmission wear over time. The TCM will adjust transmission shift pressures to compensate for wear in the multi-plate clutches. This is accomplished by monitoring the input and output speeds of the transmission. When the transmission shifts, the TCM monitors the time that it takes to accomplish the shift. The time change in gear ratio is monitored and compared to an internal time value in the TCM. If the ratio change takes more time than the stored value, the TCM will compensate by adjusting the transmission shift pressures via the EDS valve solenoids. The adaptation value is stored in the TCM. This adaptation values can only be cleared by the diagnostic
tester (DIS plus or GT-1).

The original document I had went into the fact that clutch engagement times are a function of not only the clutch plate friction characteristics, but also the fluid, since they are wet clutches. I think that is probably intuitively obvious, but I raise it because this document mentions only transmission wear, and not the specific elements that comprise that wear.

I actually owned a 3.0 X5 with the GM Powertrain transmission. Those technical documents described a very similar adaptation routine, jointly developed by BMW/Siemens/GM, and used for adaptive pressure control (APC) on those transmissions.

These sorts of control strategies, with their learning capabilities, are at the heart of why fluids last much longer. IMO.

There is another side comment, which is that understanding what the adaptations do, it makes no sense to reset them without first changing something that caused them to be at the values they are at (like a transmission or a solenoid). When people reset the adaptations because they think the adaptations are the actual problem, they are masking a symptom, not fixing something. People seem to like to reset them, though.

[Brandon002]

I'd like to see that original document, because what you posted states absolutely nothing about the transmission adapting to deteriorating fluids.

[JCL]

Originally Posted by Brandon002

So what we got out of all this back and forth banter, is that it's a matter of personal preference and what gives you peace of mind.

I always thought back and forth banter was essentially the raison d'être of discussion boards.

If people want a singular truth and to gain enlightenment, anonymous posts probably aren't the best format IMO.

[JCL]

Originally Posted by Brandon002

I'd like to see that original document, because what you posted states absolutely nothing about the transmission adapting to deteriorating fluids.

I will look for it. But in the meantime, recall that we are talking about the clutch engagement time and input/output slip ratios as inputs to a modulated clutch pressure application, for a wet clutch pack. You don't think that the boundary and hydrodynamic friction characteristics are the variables we are adapting to? We are adjusting pressure, not travel position. And if we agree that we are adapting to the friction of clutch plates as they wear, isn't that friction a function of both the clutch plate surface properties and the fluid?

There is another document posted up here somewhere that talks about the x drive transfer case. That has adaptations as well. And the control strategy is exactly the same, clutch pressure is modulated based on feedback signals. In that component, when the adaptations reach their limit (no more ability to correct for fluid properties as they change from time to time) you get a light on the dash saying fluid is out of spec. Not that clutch plates are worn, but that fluid is out of spec. Exactly the same principle.

Edit: Quoted ZF transmission document: http://www.e38.org/electran1.pdf. Still looking for the original one.

[JCL]

By request, a summary of the adaptation capabilities of the ZF transmission. The easiest document to search on was the ZF patent, so here is one of the main ones. Related patents are linked on the page.

Therefore, the problem on which this invention is based is to make a method for control of a transmission of a motor vehicle available which, for each of the different influences which impair a gear shift, a separate adaptation can be carried out from which can be deduced the respective right reaction for an optimization of a subsequent gear shift.

Note that each shift is monitored, and then adaptations are calculated for an optimization of a subsequent gear shift. The system adapts, therefore, to each of the different influences which can impair a gear shift. Full details of what they measure and how those measurements are applied to the reference condition are contained in the patent. Pretty heavy reading, but some may find it interesting.

Brandon: I humbly submit that fluid condition as it changes over time is an influence which can impair a gear shift of a wet clutch pack (each clutch pack forming a shifting element). I think we agree that fluid quality over time is an influence. ZF got a patent based on adapting to each influence. Ergo, they are adapting to fluid quality, not by direct analysis of the fluid, but by measuring the performance of the fluid.

Patent linked here:

Patent US6569060 - Method for controlling a transmission of a vehicle - Google Patenter

Interesting side note again: The patent references a specific benefit of adaptive pressure control, namely that transmission manufacturing cost is reduced due to the ability to open up the manufacturing tolerance limits. Those tolerances can be opened up because the adaptive pressure control can handle wider tolerances than a 'dumb' system. We often think of modern vehicles as being much more complicated (which they are) and at the same time more precise, which would mean more demanding on things like fluid specs and quality over time. Here is a case where precision was reduced, intentionally. That intuitively fits with the transmission being more tolerant of varying fluid condition, which is where this discussion started.

[J.Belknap]

Originally Posted by SlickGT1

Damn. I gave up on these threads lol. Glad you still at it JCL. Makes for a good read when the boredom sets in.

Agree!

[Brandon002]

It means "more tolerant" of fluid condition.

Nowhere does it state that the condition of fluid won't have any negative impact on the life of the transmission. How long will it adapt before it can adapt no longer? Again, it's an argument that can go on forever because there is no concrete, technical data to prove one theory or another.

[bcredliner]

Explaining how the transmission adapts is helpful and interesting-thanks for posting. That's is more detailed than I have read.

I am not challenging that fluid can be used a longer period of time if because of the fluid itself or the ability of the transmission to adapt to fluid performance.

My position to change the fluid is based on fluid degradation over time. I have explained how I came to that conclusion so I don't think there is any need to do it again.

The adaption capability is a great feature to extend transmission performance. As I read the how and why the transmission adapts, it also appears to endorse that part of the reason the transmission has the ability to adapt is the fluid does not perform as well over time. That when the transmission can no longer adapt the message is that the fluid is out of spec seems to be additional input that fluid degrades.

I picked 50,000 miles for a change interval out of the air. My logic is the fluid has lost enough performance that new fluid will be a worthwhile investment. I know there is not enough reliable information to verify that point of view. On the other hand, I don't think there is enough reliable information to take the position it is a bad practice. I don't think you have even implied that either, have you?

Just as you said it could be a good practice based on what I drive, it may not be worthwhile if the engine is, say, a 3.0. If I had a 3.0 I would at least extend the interval but check the fluid as often as I do now.

I don't believe in resets either, updated software yes, resets to fix a problem-- natta.

Brandon, I don't see this as banter. I think it is constructive. I respect JCl's contribution and I believe he does mine. I don't take it personal, do you?

[Brandon002]

I don't take anything on the internet personally.

I used banter as a term, I too find it informative.