Belt Sprocket Assembly Replacement Instructions for the 39278R.S
This repair will require removal of the unit from it’s mounting hardware and repair made on a bench or floor. Refer to your Owners Manual for proper assembly and carefully read and understand all warnings and cautions pertaining to your unit.
BE SURE ELECTRICAL POWER HAS BEEN DISCONNECTED FROM THE INPUT POWER LINES PRIOR TO REMOVING THE MOTOR COVER.
ANY AND ALL REPAIRS MADE TO THIS UNIT MUST BE PERFORMED WITH THE DOOR DISCONNECTED FROM THE OPENER AND IN THE CLOSED POSITION.
1. Pull emergency release cord on the carriage to disengage opener to close the garage door if necessary. (If unable to lower door using the garage door opener, use extreme caution manually closing the garage door. Before pulling the emergency release cord, make certain people and objects are clear of the garage door opening.)
2. Unplug opener power cord from power receptacle.
3. Remove Battery Backup (BBU) from powerhead if equipped:
• Unplug harness from top of powerhead.
• Remove two screws securing BBU to the rear of the powerhead.
• Tilt BBU up and slide mounting brackets out.
• Set BBU aside. FIG. 1.
4. Remove lens cover(s) by pressing top tabs down and slide lens cover(s) out. Remove light bulbs. FIG. 2.
5. Remove wall control and Safe-T-Beam® wires from the terminal block located on side of two bulb models or rear of one bulb models FIG. 3. Use a small common screwdriver to press in on orange tabs while gently pulling wires from the block. Mark wires to help facilitate replacement.
6. Remove clevis pin and hairpin from door arm assembly. FIG. 4.
7. Remove opener from mounting hardware and set opener assembly on clean work surface.
8. Remove rail assembly from powerhead:
• On belt drive models, remove two screws and belt retainer cover from rail assembly. FIG. 5.
• Remove four rail mounting screws and slide rail assembly off of the motor shaft. FIG. 6.
9. Remove the old belt Sprocket assembly from the rail assembly.
• Pull the emergency release handle down to disconnect carriage and slide out of the way. (a)
• Loosen turnbuckle lock-nuts. (7/16” wrench) (b)
• Hold chain/belt and rotate turnbuckle clockwise until threaded ends are free. (c)
• Pull the belt away from sprocket assembly.
• Remove and replace belt sprocket assembly 39278R.S. (d)
• Feed the belt around the motor sprocket. Ensure the belt is not twisted or bound.
10. Install the belt rail assembly:
• Install turnbuckle with “door” end arrow onto the gold-threaded end by rotating counter-clockwise one full turn. (a)
• Disengage carriage assembly by rotating release handle downward and insert turnbuckle through the carriage as shown.
Ensure the belt is not twisted or bound. (b)
• Continue routing the chain/belt assembly until turnbuckle is near the middle of the rail. Insert the silver threaded shaft into the
turnbuckle and rotate turnbuckle counter-clockwise one full turn. (c)
• Hold the belt and rotate turnbuckle with thumbs counter-clockwise until the belt is tensioned properly. Measure the belt tension on the opposite side of the rail until 1/4” from the bottom of the rail. (d)
• Once proper tension has been established, hold turnbuckle in place with a 7/16” or adjustable wrench. Tighten both tension
nuts with a 7/16” wrench. (e)
• Reinstall rail assembly to the powerhead. FIG.6.
• Reinstall belt guard if applicable. FIG. 5.
11. Reinstall opener assembly to mounting hardware.
12. Reinstall door arms in reverse of step 6.
13. Install wall control and Safe-TBeam wires.
14. Install light bulbs and lens cover(s).
15. Plug opener in.
16. Reset limits and fully test opener. Refer to the owners manual or visit
17. Install BBU, if equipped. Plug BBU harness into the top of the powerhead.