LiftMaster Model MJ

MJ Medium-Duty Series Logic Jackshaft Operator

The MJ is a medium-duty logic jackshift operator featuring a compact design for use on industrial sectional doors with high or vertical lift and on small rolling doors and grilles.

  • Programmable C2 or B2 wiring options (B2 requires installed Monitor Entrapment Protection Device) to meet business requirements for commercial door operator control.
  • Powerful high-starting torque ½ HP, single-phase motor with internal automatic reset thermal overload is removable without affecting limit switch settings.
  • Floor-level disconnect provides emergency manual operation.
  • Adjustable friction clutch helps protect against major damage to door and operator should the door meet an obstruction.
  • Drive Reduction, first stage heavy-duty 4L V-belt; second stage and third stages #48 chain.
  • Integrated 90 second maximum run timer.
  • Heavy-duty solenoid actuated brake standard.
  • Heavy-duty oil-filled bushings.
  • NEMA 1 type electrical box, heavy-duty 11-gauge steel frame with durable powder-coated finish, all reduction sprockets drilled and pinned to shafts.
  • Easily field converted for right or left mounting.
  • Operator/Motor Control: Solid-State Medium-Duty circuit board.
  • 3-button station for OPEN/CLOSE/STOP functions is standard for all door operators.
  • Warranty: 2 Years.
  • Built-in-3-channel, 315 MHz radio receiver accepts up to (20) LiftMaster Security+ or unlimited DIP switch remote controls. 3-button remote controls can be programmed for OPEN/CLOSE/STOP operation.
  • Integrated Timer-to-Close (TTC) for timed automatic door closure after the door reaches the full open position for added security and peace of mind. Programmable from 5-60 seconds in 5-second increments.
  • LiftMaster Commercial Door Operators comply with UL 325 standards for Monitored Entrapment Protection.
  • Control circuit: 24V NEC Class 2 control circuit


  • The MJ Operator is not recommended for use in large or high rolling doors without chain hoist modification (see Model MH).
  • On steel-insulated doors, a 24 ga. back panel is assumed.


Maximum recommended duty cycle: 12 cycles per hour.