the bushings on the motor must be worn, or loose, if you can´t service them o r they are gone, you need to grind of two "fingers" or bumps or whatever on the base of the arm, they limit the bending angle, that´s why if bushings are gone and the fingers limit the travel or swivel of the wiper arm joint, it won´t contact the glass, do a search, there are lots of threads about it with pics.