SuperBuickGuy
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I hope not too .... but .... :hpoop
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6L80 auto trans in a H3/H3T?
- Thread starter 2010H3TAlpha
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I hope not too .... but .... :hpoop
MaxPF
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I assume we're talking about an Alpha here, right? I ask because the Atlas engine (I5) has a unique bellhousing pattern that the 6L cannot adapt to. ALso, your t-case has a 27 spline input, while the 6L80 is 32 spline (same as the 4L80/85) and the 6L90 is 29 spline (same as the Allison - they are bigger metric splines, so the diameter is larger than the 32 spline 6L80 output despite having fewer splines). You may be able to find a 32 spline input for your case, but I guarantee you won't find a 29 spline input. Since you specifically asked about 6L80, availability of a 29 spline shaft wouldn't be a big deal anyway.
Swapping a 6L behind an gen IV engine/E38 ecm combo that came with a 4L80/85 is straightforward since GM did both, although platform-specific issues can still crop up (not an issue when the combo is swapped into a buggy or an older vehicle, which is usually when folks ask about using x transmission with y engine). The specific engine/ECM combo (H3 Alphas use the LH8 5.3 with the L67 ECM) you want to swap a 6 speed behind was never a combo that GM produced. As Ross explains in this thread the ECM really shouldn't care whether the TCM is the T42 (external TCM used to control 4L60/65/80/85 behind gen IV engines) or the T43 (TCM used with the 6L series - it is attached to the valve body and actually resides within the trans pan). All the ECM sees are message packets on the CAN (GMLAN) bus.
That said, the ECM and TCM tunes work together, ESPECIALLY with the 6 speeds. Unlike the 4 speeds, the 6 speeds are clutch-to-clutch designs and torque control during shifting is a critical aspect to making them shift smoothly, as well as long term reliability. Assuming the OS in the L67 ECM and the OS in the T43 don't have issues communicating with each other, significant tuning would still be required. However, depending on the specific OSes used in the ECM and TCM, one or the other may not understand some of the CAN messages being sent their way. Or they may not receive messages that they need for certain functions. There are also platform (BCM and cluster) integration questions: 6L equipped platforms have tap-shift support, which the H3 has no provisions for. The H3 may also incorrectly display gear selections with the T43 TCM. If you read the above thread that I linked, you will start to understand some of the potential pitfalls.
Swapping a 6L behind an gen IV engine/E38 ecm combo that came with a 4L80/85 is straightforward since GM did both, although platform-specific issues can still crop up (not an issue when the combo is swapped into a buggy or an older vehicle, which is usually when folks ask about using x transmission with y engine). The specific engine/ECM combo (H3 Alphas use the LH8 5.3 with the L67 ECM) you want to swap a 6 speed behind was never a combo that GM produced. As Ross explains in this thread the ECM really shouldn't care whether the TCM is the T42 (external TCM used to control 4L60/65/80/85 behind gen IV engines) or the T43 (TCM used with the 6L series - it is attached to the valve body and actually resides within the trans pan). All the ECM sees are message packets on the CAN (GMLAN) bus.
That said, the ECM and TCM tunes work together, ESPECIALLY with the 6 speeds. Unlike the 4 speeds, the 6 speeds are clutch-to-clutch designs and torque control during shifting is a critical aspect to making them shift smoothly, as well as long term reliability. Assuming the OS in the L67 ECM and the OS in the T43 don't have issues communicating with each other, significant tuning would still be required. However, depending on the specific OSes used in the ECM and TCM, one or the other may not understand some of the CAN messages being sent their way. Or they may not receive messages that they need for certain functions. There are also platform (BCM and cluster) integration questions: 6L equipped platforms have tap-shift support, which the H3 has no provisions for. The H3 may also incorrectly display gear selections with the T43 TCM. If you read the above thread that I linked, you will start to understand some of the potential pitfalls.
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If a 32 spline input exists for the BW transfer case, I have not found it in my internet research. Patc makes a 27 spline output shaft for the 4L80e which would be needed. I also did not find a 5 bolt transfer case adapter for the 4L80e either so you would need a custom transfer case adapter unless you swapped transfer cases for a passenger drop of some flavor with a standard 6 bolt pattern. Seems like everything in the driveline of this truck is a one-off including the transmission bellhousing and the transfer case adapter pattern.