dssur
+1y
The strut needs to be able to turn. The bearing at the top of struts is there for this purpose. if you put a bag between the bearing and the strut (or even above the bearing) there will be nothing to hold the strut rigid and the top of the strut will swing around, wildly changing camber, caster, toe, steering direction etc.
The "shock" in struts is made to support the car, you cant do that with a shock. It is also made to stay rigid and only allow the spindle to move straight up and straight down. If you put a bag in its place, it will be like replacing your suspension with spaghetti.