A wiper arm assembly is adapted to support a wiper blade as it moves across a surface to be wiped. The wiper arm assembly includes a body and a head supported by the body and adapted to be mounted to a pivot shaft that defines a pivot axis P and drives the wiper blade in an oscillating manner across the surface to be wiped. The body also includes an opening providing access to the head mounted to the pivot shaft. The wiper arm assembly includes a cover pivotally mounted to the body at the opening and is movable about an axis A substantially perpendicular to the pivot axis P from a first position closing the opening to a second position allowing access to the head. A locking mechanism on the cover locks the cover to a nut on the pivot shaft to retain the cover in the first position closing the opening.