ego mower blade stops spinning when i hit tall grass, but the motor is still running.

Diagnosis

This failure occurs when there is a mechanical disconnection between the motor's drive shaft and the cutting blade. In the EGO LM2135SP, the motor is designed to continue humming or rotating internally even if the blade has ceased motion. This is typically caused by the failure of the blade adapter or the loosening of the prevailing torque hexagon lock nut (part number 5630351002). When you hit thick, tall grass, the sudden increase in resistance creates a torque spike that overcomes the friction of a loose nut, causing the shaft to spin inside the blade hole without transferring energy to the blade. Alternatively, the internal splines of the blade adapter or the motor shaft itself may have stripped. If the metal teeth (splines) that lock the motor shaft to the blade are worn down or sheared, the motor will spin freely while the blade remains stationary. You can confirm this by removing the battery and attempting to rotate the blade by hand; if it spins with zero resistance or "clicks" while rotating, the mechanical link is broken. If the motor shuts off entirely with an error code on the LED display, it is an electrical overload; however, if the motor keeps running while the blade stops, it is strictly a mechanical failure of the drive assembly.

How to Fix It

1. Safety First: Remove the 56V battery immediately. Ensure the mower is on a flat, stable surface and tilt it backward (motor side up). Never tilt the mower forward, as this can cause the battery to shift or damage the electronics.
2. Access the Blade: Use a 7/16" or 11mm socket wrench to locate the prevailing torque hexagon lock nut (5630351002) and the associated washer (5650705002).
3. Inspect for Looseness: Attempt to tighten the nut. If it spins easily without resistance, the nut has lost its locking capability and must be replaced.
4. Check the Splines: Completely remove the nut and lift the blade (part number 3707494002) off the shaft. Inspect the center hole of the blade and the motor shaft for "rounding" or smoothed-out metal teeth. If the splines are flat or stripped, the blade and the adapter must be replaced.
5. Reinstallation: Place the washer back on the shaft, align the blade, and thread the new lock nut. Tighten the nut firmly. Use a torque wrench to ensure it is seated tightly against the blade to prevent future slippage.
6. Test Run: Reinsert the battery and start the mower in a clear area before returning to the tall grass.

If That Didn't Work

• Replace the Blade Adapter: If the motor shaft is spinning but the blade isn't, and the nut is tight, the internal adapter sleeve may have failed. Replace the adapter assembly to ensure a tight friction fit between the motor output and the blade.
• Inspect for Debris Jam: Check the underside of the deck for "wrapped" grass or thick vines around the blade spindle. Even if the motor is running, a physical obstruction can act as a brake, causing the blade to slip on the shaft. Use a putty knife to scrape the underside of the deck clean.
• Check for Bent Blade: A severely bent blade can create an unbalanced centrifugal force that puts uneven pressure on the shaft, leading to premature stripping of the splines. Replace the blade if any warping is visible.
• Evaluate Grass Height: If the motor is running but the blade stops specifically in tall grass, you may be overloading the system. Raise the cutting height to the highest setting and mow the tall grass in two passes to reduce the torque load on the drive shaft.

Heads Up

• Avoid "Hitting" Objects: Striking a rock or thick root can instantly strip the splines of the motor shaft, which often requires a full motor assembly replacement (part number 2730252001) rather than just a new blade.
• Regular Tightening: Check the blade nut every 10 hours of operation. The vibration from high-RPM cutting can gradually loosen the lock nut over time.
• Blade Sharpening: Dull blades increase the drag and resistance on the motor, which increases the likelihood of the blade slipping or the motor overheating. Sharpen blades every season.
• Clean the Deck: Dried grass buildup under the deck restricts airflow, forcing the motor to work harder and increasing the mechanical stress on the blade adapter.