Liftmaster K75-19981 Arm Kit, H
The LiftMaster K75-19981 arm kit is a commercial operator arm kit used in select LiftMaster Model H and HJ operator mechanical assemblies. The arm kit works with the manual operation, disconnect, frame, and drive hardware so the operator can transfer movement correctly and release according to its design. If the arm is bent, worn at pivot points, loose, or binding, the operator may have rough manual action, alignment problems, or inconsistent operation.
This part is commonly described as Arm Kit H, Arm Kit Model H/HJ, or Arm Kit - Left in H/J/HJ replacement-parts diagrams. It should not be confused with K75-19977, which is commonly tied to Model J arm or disconnect applications. In the Model H parts diagram, K75-19981 is shown near frame plate kits, sprocket assembly, pulley assembly, cogged belt, and motor pulley items. In HJ references, it may be used with hoist/jackshaft-specific clutch and frame hardware.
A deeper compatibility check found strong references for H and HJ commercial door operators, with some supplier references also listing DH and DHJ. Because those broader model families can vary by generation and configuration, the safest ordering method is to confirm K75-19981 in the exact parts diagram for the operator being serviced.
Compatible With
This arm kit is tied most strongly to LiftMaster H and HJ commercial operator applications.
- LiftMaster Model H commercial door operators where K75-19981 is listed as the H arm kit or arm kit Model H/HJ.
- LiftMaster Model HJ commercial hoist/jackshaft operators where K75-19981 is listed in the arm kit position.
- Post-2005 Logic 4.0 and Logic 5.0 H and HJ mechanical diagrams where K75-19981 appears near the frame and disconnect hardware.
- Select H3311, H3321, H3323, H3338, H3343, H3353, H5011, H5021, H5023, H5038, H5043, H5053, H7511, H7521, H7523, H7538, H7543, H7553, H1011, H1021, H1023, H1038, H1043, and H1053 style Model H families when the suffix/generation and diagram match.
- Select HJ3311, HJ5011, HJ7511, HJ1011 and related HJ horsepower/voltage families when the diagram calls for K75-19981.
- Some supplier references also list DH and DHJ model families; verify by parts diagram before ordering for those units.
- Not the same as K75-19977 Arm Kit J / disconnect arm kit.
Also Known As / Related Part Numbers
Features & Specifications
| Feature / Specification | Details |
|---|
| Manufacturer | LiftMaster / Chamberlain |
| Product Type | Commercial operator arm kit |
| Part Number | K75-19981 |
| Application | H / HJ arm or disconnect hardware area |
| Primary Operator Families | LiftMaster H and HJ commercial door operators |
| Supplier-Referenced Families | DH and DHJ may be listed by some suppliers; verify by diagram |
| Related Companion Part | K75-19977 for J applications |
| Notes | Do not mix H-arm and J-arm kits without diagram confirmation |
Technician Note
If the original arm kit is bent or binding, inspect the frame plate, disconnect hardware, shaft alignment, and door balance. Heavy manual force or a door that is not balanced can damage the replacement arm kit.
Before Ordering
- Confirm K75-19981 in the H, HJ, DH, or DHJ parts diagram.
- Do not confuse this with K75-19977 J arm kit.
- Inspect pivot points, springs, chain/cable hardware, frame plates, and fasteners.
- Confirm the door moves freely before reconnecting the operator.
- Use a commercial door technician if the release system does not move smoothly.
Professional Advisory
Commercial door operator mechanical parts should be installed with the operator power disconnected and the door properly secured. Do not service a hoist, jackshaft, slide gate, or industrial door operator that has a damaged door, broken spring, unsafe counterbalance, missing entrapment protection, or uncontrolled movement. Use a qualified commercial door or gate technician when alignment, high-voltage wiring, brake work, or operator safety devices are involved.
Product Questions & Answers
Is K75-19981 for Model H or Model J?
K75-19981 is commonly associated with Model H and HJ applications. Model J applications more commonly reference K75-19977.
Why do some diagrams call this Arm Kit - Left?
Some H/J/HJ parts diagrams describe the arm position by side. Always match the part number and operator diagram rather than only the wording.
Does this fit DH or DHJ operators?
Some supplier references list DH and DHJ compatibility, but those applications should be verified with the exact parts diagram.
What should be inspected with this arm kit?
Inspect frame plates, pivot hardware, springs, chain or cable components, and the manual release path.
Can a worn arm kit affect safety?
Yes. A binding or damaged arm kit can affect manual operation and operator control. The commercial door should be serviced before being returned to use.
