Car don't stop moving

I made this kind of heavy load cart with physics.
It is using a normal actor blueprint. The wheels have a sphere for the collision and they are attached to the cart base with constraints.
It works but when I push the cart with the character the speed don’t go lower than ~6.5, so after the push it slows down until it get ~6.5, then it keeps moving at that speed slowly forever until it hits a wall of something else

thanks in advance