Quote:
Shift points and torque converter lockup are soley determined by software.
Not entirely true, especially in real world environments, with lowest cost vendors supplying mass production TC's. The TCM software is part of a system, and is radically affected by the quality of the hardware it is working with. Since TC lockup isn't just a simple "LOCK" at a specific rpm, going from full unlocked to full locked, but is electronically modulated as lockup speed/rpm is approached, the coupling characteristics of the TC clutch will dramatically affect TC lockup behavior and the real rpm at which it occurs. A point I notice you fail to mention. Or possibly don't realize.
The TCM software uses sensors and feedback from the mechanicals of the transmission to "tell" it when to shift. If you modify the mechanical behavior you indirectly affect the TCM programming and affect a change in shift performance. Notice what I said in underline text below - that modifed pump pressure at which TC lockup occurs, as well as the accumulator spring rate can modify the shifting behavior. The italic word "where" should have been "when." But I stand by my assertion that a higher quality TC can lockup and stay locked at a lower rpm than a loose, poor quality TC regardless of the software trying to adjust for mechanical variance and cvi's. Especially when the same line pressure keeps one TC locked(and resulting engine rpm low) and another lower quality TC slips badly at the same rpm, then "tells" the TCM that the engine rpm is too high for what the TCM is willing to accept for a given tc lock range.
With the TC/shiftkit mod, in reality, TC lockup performance at lower speeds is more positive, lacking the slop present in the factory TC, and comes earlier in the shift/rpm curve. It doesn't matter what the software attempts to do or is programmed to do, if the stock TC hardware isn't able to handle it effectively. I believe that is the heart of the CRD TC issue - not software problems, just cheap TC hardware.
If the TC lockup was soley affected by software alone and using a fixed rpm point, this would not be possible. But since the TC clutch lockup is electronically modulated as it approaches lockup, the lockup behavior of TC and the rpm at which it occurs is highly affected by the amount of slip/loss present in the TC. As you know, the factory TC has lots of slip (or slop, whichever term you prefer). It is far from optimized or even consistent in behavior from TC to TC, as I learned from having 2 factory TC's in a 12 month period. Major driving behavioral changes from one TC to another factory TC, and neither one very good. Where was the software control on that one? Lockup behavior was so bad on the 2nd oem TC that I could not even feel the 62 mph lock. Ever. It sorta of wallowed into high gear is the best description I can think of. With the SunCoast/Shiftkit snakeoil combination, it is now a crisp, definite pleasant shift, with a definite slight tachometer drop. Same software. Radically better performance.
While the TCM program rpm shiftpoints are not modified, the TC lockup holding behavior is much improved with the new TC/shiftkit, especially at lower rpm, I believe from improved modulated lockup behavior just prior to full TC lockup. It may in fact end up locking at lower rpm than the factory TC due to the excessive locking/unlocking slipping syndrome that the factory TC suffers from.
While what you state should be true in theory in a perfect transmission design, I believe is not happening in real world driving due to excessive slip/looseness/parasitic loss in the factory TC, preventing the TCM from keeping the TC lockup duty cycle high enough as it approaches programmed lockup points. Those very electronic controls are directly affected/somewhat overwhelmed by the poor factory TC performance.
So while the programming is not changed, the lockup behavior is altered for the better and TC lockup is occurring more often and at lower rpm than with the factory TC.
Regards,
Ranger1
Unless something like a professional TransGo Shiftkit modifies the pressure setting in the tranny pump, via a new set of pressure relief springs, at which the TC lockup occurs, as well as modifying where shift points occur with new springs in the valve body. For the home version, they supply a resistor to change the pump line pressure.
Then there is the matter of the torque multiplier in the TC bringing on more power faster due to higher efficiency and more torque multiplication at the same engine rpm and electronic setpoints from the TCM.[/quote]
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