Bobby,
Here's the top view of a truck:
There's a keyed section on top of it (outlined in red below because it's very hard to see above):
Remove the truck with the loose collector by turning it 90 degrees so that the keyed section on top of it (in red above) will drop down through the keyhole in the center of this mounting plate, which is attached to the frame:
Once it's out the rest should be easy, and then reverse this process to put the truck back.
Mike