Quote:
Originally Posted by mkoesel
Although I don't know for absolute certain, I believe the TCU disengages all shift collars just as would be the case with a manual transmission with the shifter is in the neutral position.
It is true that the TCU could technically just open both clutches and call that state "neutral", leaving one or two shift collars engaged. However it makes more sense to put the transmission into a true neutral state, if for no other reason, in case a clutch were to be engaged due to some failure in the hydraulic system. One might put the transmission in neutral and exit the vehicle for an extended period of time, and merely relying on the clutch remaining open to keep the car from moving would be unnecessarily precarious.
Whether the TCU also keeps both clutches open at that point, I don't know.
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As far as I know the clutches are “normally” open on the DCT and hydraulic pressure is required to close them. This is opposite to a standard manual transmission where the clutch is normally closed and outside force (the foot pressing on the clutch pedal) is required to open it. So when the engine is shut down, there is no more hydraulic pressure in the DCT and both clutches open.
Ragarding the neutral position for the transmission, the diagram in the F8X technical training doc shows a true neutral with none of the gear dogs engaged.