The LiftMaster K75-12870 Straight and Curved Door Arm Kit is an OEM replacement assembly that connects a trolley-style LiftMaster garage door opener to the door. The two-piece design provides the correct linkage geometry between the opener’s trolley/shuttle and the top door bracket, helping ensure smooth opening and closing through the full travel. Use this kit when repairing a bent or damaged door arm or when completing an installation that specifies K75-12870 in the model’s parts breakdown.
This door arm kit includes the straight and curved arm sections identified by LiftMaster under part number K75-12870. Installation typically involves fastening the straight arm to the opener’s trolley and the curved arm to the door’s top bracket, then selecting the appropriate mounting holes to achieve proper door travel as directed in the operator’s manual. For safety, disconnect power and secure the door before service, and verify compatibility by checking your opener’s parts diagram or service manual for the exact part number. Designed for sectional overhead doors on select LiftMaster trolley operators, this genuine replacement helps restore reliable performance in residential or commercial applications where K75-12870 is specified.
| Operator Series | Compatible Models | Operator Type |
|---|---|---|
| T Series | T, T331, T501, T751, T101 | Industrial Trolley |
| MT Series | MT, MT3311, MT5011 | Medium Duty Trolley |
| GT Series | GT, GT501, GT751, GT101 | Heavy Industrial Trolley |
| MAXUM Series | TDC (All Maxum Trolley) | DC Next Gen Trolley |
| Logic Versions | Logic 3.0, 4.0, and 5.0 | All Circuit Board Units |