Abstract: A retractable undercarriage for mounting dual wheels for a large transport vehicle comprising a support member adapted for connection to the vehicle and having a vertically extending leg and an arm member pivotally connected to one end thereof to the lower end of the leg by a special pin connection employing ring bearings. A running gear sub-assembly is connected to the other end of the arm member. First and second mounting blocks are respectively attached to an upper portion of the support member and to the arm member. Each of these blocks has a slot formed therein for receiving a pivot pin, which slot is open at one end. A hydraulic cylinder mechanism extends and retracts the undercarriage by pivoting the arm member. The upper and lower ends of this mechanism are pivotally connected by the pivot pins to the mounting blocks. Threaded fasteners secure the pivot pins in their respective slots.