When your garage door opener grinds loudly but the door stays put, you’re dealing with an internal opener failure, not a spring or cable problem. The motor is running, but something inside has broken or slipped, preventing power from reaching the door itself.

Before I dive into internal causes, always rule out one external issue first: pull the red emergency release cord hanging from the trolley to disconnect the door from the opener. If the door opens smoothly by hand with no resistance, the problem is definitely inside the opener unit, not with your springs or tracks.

Stripped Drive Gear: The Number One Culprit

The most common cause I see in San Diego homes is a stripped nylon drive gear. This white plastic gear sits at the top of the motor and meshes with the metal drive sprocket to move the chain or belt.

Over time, especially on older chain-drive openers, this gear wears down and eventually strips completely. When it fails, the motor spins freely with a loud grinding sound, but nothing engages. You’ll often see white plastic shavings scattered inside the opener housing, a telltale sign the gear has disintegrated.

This part costs between $15 and $30, but replacing it requires disassembling the opener head, which most homeowners find tricky. Our team handles these repairs quickly because we stock the right gears for all major brands, whether for residential systems or Commercial Garage Door Repair needs.

Other Internal Opener Failures

If it’s not the drive gear, here are the other mechanical issues that cause grinding without movement:

  • Worn drive sprocket: The metal sprocket above the gear can develop worn teeth, causing the chain or belt to slip and grind without moving the door.
  • Derailed chain or belt: Look up at the rail. If the chain hangs loose or the belt has jumped off its track, the motor will spin but nothing moves. This sometimes happens after a manual door slam or impact.
  • Failed start capacitor: The motor hums loudly or buzzes but can’t generate enough torque to turn. You may notice a burning electrical smell. This is more common in coastal San Diego areas where salt air accelerates electrical component corrosion.
  • Broken trolley carriage: The plastic trolley that rides along the rail can crack or break internally, disconnecting the drive mechanism even though the chain moves.

Why This Requires Professional Diagnosis

While the symptoms are clear, pinpointing the exact failed component requires opening the opener housing and inspecting internal parts. Many homeowners mistake a stripped gear for a motor failure and replace the entire unit unnecessarily.

I also check the door balance and spring tension during these calls. A door that’s too heavy due to a weakened spring will overwork the opener and accelerate gear wear, turning a simple repair into a recurring problem. For other opener issues, see Your Garage Door Remote Stopped Working But The Battery Is Fine: Here’s Why for troubleshooting guidance.

If your garage door opener is grinding but not moving in San Diego, our team at Best Garage Door & Gate Repair Services can diagnose and repair it the same day in most cases. We carry common drive gears, sprockets, and capacitors on our trucks. Call us at (619) 877-6218 for fast, reliable service backed by our contractor license and warranty.