It appears that the Walthers track cleaning car uses springs between the cleaning pad and the underside of the car to keep the cleaning pad in contact with the rails.
True it does have springs
Unless the car is extra heavy, such springs could intefere with the cars normal tracking over the rails.
Also true if were not extra heavy. It is: 0.7 ounces over NMRA guidelines. So far it hasn't ripped the couplers off.
Henry
COB Potomac & Northern
Shenandoah Valley