Dmax/Alison shifts inconsistant
Ranger Pro
11-06-2005, 01:21 AM
I bought my first Dmax with an Alison and I think it might have been a mistake. I have been told by the dealer that it is normal to have a hesitant slip between 2&3, but about once every 100-200 miles I get a bad shift into drive as well as other irregular shifts. The problem is inconsistant enough that the dealer can't make it fail when they look at it. The last time I took it in they replaced a solenoid on the trans. It worked well for about 1,500 miles and now it's doing it again. The bad shift is bad enough to lock your seat belt forward when it does it bad. It also sounds bad. I had a radiator bracket on an old Nissan 4x4 break loose one time and when I would accelerate the radiator would fall into the fan and this sounds just like that. It's bad enough that my wife notices it. She usually doesn't notice anything until the wheels fall off or it doesn't move anymore. Is this normal? It has been to the dealer 3 times for this and they make me feel like it's me. I do love GM vehicles but I feel a little helpless.
GMMerlin
11-06-2005, 05:24 AM
Allisons use a shift strategy called "adaptive shifting"
Sometimes a harsh shift is caused by the TCM learning a shift while the vehicle is loaded and will perform the same shift unloaded (like you were pulling a trailer) the second shift will have higher line pressure so it will feel firmer.
Here is an explination
The transmission control module (TCM) produces excellent shift quality by applying closed loop control that constantly adjusts shift characteristics for changes in operating conditions. These adjustments are based on vehicle conditions, such as grade, load, and engine power.
The learning process of comparing and adjusting shift parameters is referred to as adaptive control. Adaptive control establishes initial conditions for shifts and makes during shift adjustments. The TCM constantly monitors operating conditions, such as battery voltage and transmission sump temperature, and adjusts shift parameters accordingly. After a shift is completed, the TCM compares the shift to a target shift profile in the TCM calibration and makes adjustments before the next shift of the same kind is made.
If you are experiencing harsh shifts, it is important to verify whether the particular shift is converged. Use the scan tool in order to determine if the shift is converged.
• If the shift is not converged, the TCM is learning how to adapt that shift, and needs to be driven more, with the intention of performing more of the particular type of shift.
• If a particular shift is converged, but still objectionable, it is good troubleshooting practice to reset the adaptive values for that shift back to base calibration level. This will automatically reset the TCM to fast adaptive mode. The vehicle should then be driven in order to allow the TCM to relearn the shift. Many times this will correct the condition. It is possible to reset individual shifts without affecting the other shifts.
Sometimes a harsh shift is caused by the TCM learning a shift while the vehicle is loaded and will perform the same shift unloaded (like you were pulling a trailer) the second shift will have higher line pressure so it will feel firmer.
Here is an explination
The transmission control module (TCM) produces excellent shift quality by applying closed loop control that constantly adjusts shift characteristics for changes in operating conditions. These adjustments are based on vehicle conditions, such as grade, load, and engine power.
The learning process of comparing and adjusting shift parameters is referred to as adaptive control. Adaptive control establishes initial conditions for shifts and makes during shift adjustments. The TCM constantly monitors operating conditions, such as battery voltage and transmission sump temperature, and adjusts shift parameters accordingly. After a shift is completed, the TCM compares the shift to a target shift profile in the TCM calibration and makes adjustments before the next shift of the same kind is made.
If you are experiencing harsh shifts, it is important to verify whether the particular shift is converged. Use the scan tool in order to determine if the shift is converged.
• If the shift is not converged, the TCM is learning how to adapt that shift, and needs to be driven more, with the intention of performing more of the particular type of shift.
• If a particular shift is converged, but still objectionable, it is good troubleshooting practice to reset the adaptive values for that shift back to base calibration level. This will automatically reset the TCM to fast adaptive mode. The vehicle should then be driven in order to allow the TCM to relearn the shift. Many times this will correct the condition. It is possible to reset individual shifts without affecting the other shifts.
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