The Marantec 188818 Straight Extension Arm (also listed as 00188818) is an OEM replacement door arm for Marantec residential garage door openers. This component forms the straight section of the two-piece door arm assembly, connecting the opener trolley’s curved door arm to the garage door’s top bracket. It restores proper door travel and alignment when the original arm is bent, missing, or worn. Commonly used on sectional overhead doors, it is designed for many Marantec belt- and chain-drive operators, including Synergy and legacy M-Line units; confirm fitment by checking your opener’s parts diagram or owner’s manual.
Installation typically reuses the opener’s existing clevis and cotter pins. The arm’s multiple adjustment holes allow fine-tuning of door travel and rail angle to reduce strain on the opener and ensure smooth operation. For safe setup, disconnect power to the operator, pull the manual release, support the door, and make adjustments with the door fully closed in accordance with Marantec instructions; because garage door systems are spring powered, service by a qualified technician is recommended. This genuine Marantec replacement part helps maintain correct door geometry and reliable performance of compatible trolley-style operators.