It's not a ton. But it's not zero. Somewhere in between.
The only force that acts on the crossmember, aside from the weight of the trans, is from the forces that the driveshaft imparts on it under a launch. Now, I'm not entirely sure how a driveshaft can push up on the tailshaft of a transmission, but it definitely happens under load. Ask anyone who's ripped a stock trans biscuit in half and had to listen to the transmission slapping the floorpan every time they hit the gas!
Is it a HUGE amount of force? I doubt it. But it can be substantial for a hard-launching car.
