Liftmaster K72-33875 Output Shaft and Sprocket

Liftmaster K72-33875 Output Shaft and Sprocket

The LiftMaster K72-33875 is a replacement output shaft and sprocket component for select MT and BMT medium-duty trolley commercial door operators. It is part of the mechanical drive section that transfers motor output through the operator's chain and sprocket system.

This part is commonly cross-referenced under older or alternate part numbers. It should be ordered from the operator parts diagram because output shaft kits can look similar across LiftMaster commercial operator families.

Compatibility and Application

Deep search results consistently tie K72-33875 to LiftMaster MT and BMT medium-duty trolley commercial door operators. The MJ jackshaft parts breakdown uses a different output shaft and sprocket kit, so this part should not be treated as a universal medium-duty output shaft.

• LiftMaster MT medium-duty trolley commercial door operators
• LiftMaster BMT medium-duty trolley commercial door operators
• MT5011 / BMT5011 style trolley operator applications where the parts diagram calls for K72-33875
• Commercial trolley operator drive assemblies using related references K72-12471, K7212471, 308115111, or 308115111K

Important Fitment Notes

• Not the same as the MJ output shaft and sprocket kit K72-33962
• Not a complete clutch shaft kit unless the listing packaging confirms included parts
• Not selected by sprocket appearance alone
• Not for chain, belt, or jackshaft operators outside the specified MT/BMT parts family

Features & Specifications

Also Known As / Related Part Numbers

• K72-33875
• K72-12471
• K7212471
• 308115111
• 308115111K
• LiftMaster output shaft and sprocket
• MT/BMT output shaft kit

Related Parts in the Same Operator Family

• K72-33962 - MJ output shaft and sprocket, not the same kit
• 11-10319 - output shaft reference in older MT/BMT parts sections
• 15-48B10GXX / 15-48B10G1 - sprocket references in related output sections
• 19-48027M / 19-48033M - chain references in related output sections
• 12-10029 - 3/4 inch bearing reference in related output sections

Technician Notes

A worn output shaft or sprocket may cause chain jump, uneven travel, grinding, visible shaft wobble, or excessive backlash. Check the chain and sprocket set together, not one piece in isolation.

If the output shaft failed from overload, inspect door balance, track drag, clutch setting, and the trolley/door arm connection before returning the operator to service.

Before Ordering Checklist

• Confirm the operator is an MT or BMT medium-duty trolley model
• Confirm the diagram lists K72-33875 or a related number such as K72-12471
• Inspect sprocket tooth wear and chain stretch
• Check bearings, keys, roll pins, snap rings, and shaft alignment
• Do not substitute MJ output shaft kit K72-33962

Professional Advisory

Drive-shaft service involves stored door load and moving mechanical components. Secure the door, disconnect power, and have a qualified commercial door technician inspect the drive system and safety devices after repair.

Product Q&A

Which operators use K72-33875?

K72-33875 is commonly listed for LiftMaster MT and BMT medium-duty trolley commercial door operators.

What are the related part numbers for K72-33875?

Common related numbers include 308115111, 308115111K, K7212471, and K72-12471.

Is this the MJ output shaft kit?

No. MJ jackshaft operator references show a different output shaft and sprocket kit, commonly K72-33962.

What symptoms point to a worn output shaft or sprocket?

Chain jumping, uneven travel, grinding, shaft wobble, sprocket wear, or excessive drive backlash can point to output shaft or sprocket wear.

Should the chain be inspected when replacing this part?

Yes. Chain wear, sprocket wear, bearing play, and alignment should all be checked together.