A road surface planner having a coupling mechanism coupled between a working tool attachment and a transporter to permit independent movement (i.e., rotation and/or pivoting) between the transporter and the attachment is provided. The attachment can have a rotary driven element such as a grinding element for modifying an irregular surface of existing pavement. The rotary element can be supported by a rear frame with a rear wheel assembly, a boom at the front of the grinding element, and a front wheel assembly coupled to the boom. The coupling mechanism can include a first member pivotably coupled to the transporter, and a second member fixed to the rear frame. The first member has a central opening defined by an inner edge for slidably contacting along a hub that extends from the second member for rotation there along.