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The transmission service manuals have to be purchased, but their user manual is available for download. http://www.allisontransmission.com/servlet/DownloadFile?Dir=publications/pubs&FileToGet=OM1334EN.pdf There is a section on lockup clutch function. It is not clear whether the lockup...

Without some sort of brake input to the trans, the only other way I could see the TCC disengaging is if it were designed to on a decel, via hydraulic circuits and the throttle input. I cannot tell with those schematics if your trans does or not, nor do I have any such charts for the MT654. But...

I cannot find any input in the schematics, electrical or pneumatic, that would "tell" the transmission that the brakes are being applied. The transmission shift points and TCC apply are controlled by the modulator, but this is only the throttle position input to the trans. Unless there is some...

I have a suspicion that TCC disengagement from heavy accel or braking is not done at all on the M939. I can feel the TCC engage, but have never felt it re-engage after say, braking at moderate speed and then getting back into the throttle. I just don't see how the trans would know you are...

Bjorn, my understanding of the 939 torque converter is that it locks in towards the top of 2nd gear and stays locked in for the rest of the upshifts. I can feel this as sort of an extra 1/2 gear "shift" right before going into 3rd. In the civvy junk, a brake pedal electronic input kicks out...