garage door opener makes a loud grinding or screeching noise only when going up. it's a legacy 920.

Diagnosis

When an Overhead Door Legacy 920 makes a loud grinding or screeching noise exclusively during the ascent, it indicates a failure of the drive system to maintain grip under maximum load. Because the motor must work harder to lift the weight of the door than it does to lower it, the friction requirements are higher. The screeching is typically "belt slip," where the rubber belt is sliding across the metal surfaces of the motor pulley or the idler pulley rather than gripping them. This is caused by one of three things: the belt has stretched beyond its operational tolerance, the rubber has "glazed" (become hard and shiny from heat and friction), or the idler pulley tensioner has vibrated loose. To confirm this, open the motor housing and watch the drive pulley while the door begins to move upward. If you see the pulley spinning for a fraction of a second before the belt catches, or if the belt visibly oscillates/slaps, you have a tension or wear issue. If the noise is a metallic grinding rather than a rubber screech, the internal bearings of the idler pulley have likely collapsed, causing the pulley to seize and the belt to rub against a non-rotating surface.

How to Fix It

To resolve this, you must first assess the physical condition of the belt and then calibrate the tension of the idler assembly.

1. Disconnect Power: Unplug the Legacy 920 from the 120V outlet to prevent accidental activation while your fingers are near the drive pulley.
2. Visual Inspection: Inspect the entire length of the belt. Look for "glazing"—smooth, shiny spots on the inner ribs. If the belt looks like polished plastic, it must be replaced (Part # varies by rail length), as tensioning a glazed belt will only cause it to snap.
3. Access the Idler: Locate the idler pulley assembly, which is the tensioning mechanism situated between the motor and the trolley.
4. Loosen the Locknut: Using a 1/2-inch wrench or socket, loosen the locknut on the tensioning bolt. Do not remove the nut entirely; just break the seal.
5. Adjust Tension: Turn the adjustment bolt clockwise in small increments (1/4 turns). This moves the idler pulley away from the motor, increasing the tension on the belt.
6. The "Thumb Test": Press firmly on the center of the belt span between the motor and the idler. There should be approximately 1/4 inch to 1/2 inch of deflection. If the belt is rigid like a guitar string, it is too tight and will warp the motor shaft; if it flops, it is too loose.
7. Lock and Test: Tighten the locknut firmly to secure the position. Plug the unit back in and run the door through three full cycles. The screeching should be eliminated.

If That Didn't Work

• Replace the Drive Belt: If the belt shows fraying on the edges or the ribs are missing, tensioning will not work. Remove the motor head from the rail, slide the old belt off the drive sprocket, and install a new reinforced rubber belt. Ensure the belt is seated fully in the grooves of the motor pulley before tightening.
• Lubricate the Rail and Rollers: Sometimes the "grinding" isn't the belt, but the motor struggling against a bound door. Use a high-quality silicone spray or lithium grease on the rollers and hinges. If the door is hard to lift manually, the motor will strain, causing the belt to slip.
• Replace the Idler Pulley Bearing: If the noise persists and sounds metallic, the bearing inside the idler pulley has failed. You will notice the pulley does not spin freely by hand. Replace the entire idler assembly to restore smooth rotation.
• Check the Motor Capacitor: If the motor "stutters" before the noise starts, the start capacitor may be failing. This causes a momentary lag in torque, which makes the belt slip violently during the initial lift. Replace the capacitor if the motor hums before the belt catches.

Heads Up

• Avoid Over-Tensioning: Never tighten the belt to the point of zero deflection. Over-tensioning puts excessive lateral load on the motor bearings and can lead to a premature motor burnout or a snapped belt.
• Avoid WD-40: Never apply WD-40 or oil to the rubber belt. These petroleum-based products degrade the rubber compound, causing the belt to stretch and slip even more.
• Balance the Door: Always test your door's balance by disconnecting the opener and lifting the door halfway by hand. If it doesn't stay in place, your springs are worn. A heavy door will destroy a Legacy 920 belt regardless of how well it is tensioned.
• Annual Inspection: Check the belt tension every autumn and spring. Temperature swings cause the rubber to expand and contract, which naturally loosens the idler bolt over time.