the cutting height adjustment knob just spins freely, won't change the height anymore.

Diagnosis

The issue is caused by the failure of the internal plastic drive gear or the stripping of the splines within the height adjustment assembly. In the Husqvarna Automower 430XH, the adjustment knob translates rotational movement into vertical movement of the cutting disc via a series of plastic gears. Over time, debris buildup, grit, or repeated adjustments under tension cause the teeth of these gears to shear off or wear down until they no longer mesh. You can confirm this by turning the knob and listening closely; if you hear a faint clicking or "skipping" sound, the gear teeth are stripped. If the knob spins with zero resistance and makes no sound, the drive shaft has likely snapped or completely detached from the gear housing. Because the 430XH is designed for tougher terrain, the increased vibration can accelerate the fatigue of these plastic components compared to the smaller 300-series models.

How to Fix It

To resolve this, you must replace the height adjustment assembly. You will need a Torx T20 screwdriver and a clean workspace to avoid contaminating the chassis.

1. Power down the mower completely and remove the battery to ensure there is no risk of accidental blade activation.
2. Flip the mower onto its back or use a mower stand to gain clear access to the underside.
3. Remove the central cover plate located directly beneath the cutting disc. This requires loosening the perimeter screws using the T20 driver.
4. Carefully slide the blade disc assembly downward. Be mindful not to drop the cutting blades; if they fall, ensure they are cleaned before re-installation.
5. Locate the height adjustment gear housing. You will see the plastic assembly that connects the external knob to the internal lift mechanism. Unclip the housing by depressing the side retaining tabs and pulling the assembly straight out of the chassis.
6. Insert the new height adjustment assembly (Part No. 532131111 or equivalent for 430XH series) into the slot. Press firmly until you hear a distinct "click," confirming the retaining tabs have locked.
7. Slide the blade disc back into position, ensuring it seats fully against the new gear mechanism.
8. Reinstall the cover plate and tighten the screws firmly, but do not over-torque them as the plastic housing can crack.
9. Reinsert the battery and test the knob. Rotate it through the full range (typically 60mm to 150mm) to ensure the disc moves vertically without slipping.

If That Didn't Work

• Check the Mating Chassis Gear. If the replacement knob still spins, the problem is likely the drive gear integrated into the mower's main chassis. If the teeth on the chassis side are worn flat, a new knob assembly won't have anything to grip. This requires a deeper teardown of the chassis to replace the internal drive gear.
• Inspect for Debris Obstruction. A small pebble or a clump of dried grass may be wedged between the gear teeth and the lift arm. Use compressed air or a thin pick tool to clear the gear tracks completely before attempting another installation.
• Verify Blade Disc Alignment. If the blade disc is slightly warped or bent, it can put lateral pressure on the adjustment gear, causing it to pop out of alignment. Check the disc for any signs of impact damage or bending.
• Lubricate the Threaded Rod. Sometimes the gear is fine, but the threaded lift rod is seized due to corrosion. Apply a small amount of lithium-based grease to the lift screw to ensure the gear can actually turn the mechanism.

Heads Up

• Avoid forcing the knob past its stop points. Forcing the dial beyond the minimum or maximum height setting is the primary cause of stripped gears.
• Clean the underside of the mower with a brush after every 20 hours of operation to prevent grit from entering the gear housing.
• Always check that the blade disc is seated perfectly flush before tightening the cover plate; an uneven seat puts uneven torque on the height adjustment gears.
• When replacing the assembly, check the condition of your cutting blades. Dull blades increase vibration, which puts additional stress on the plastic gear components.