wheel wobbles side to side even with a new disc and tight nut, seems like the shaft is bent.

Diagnosis

The side-to-side wobble in the Makita XAG04Z typically stems from a deformation of the output spindle shaft or a failure of the internal spindle bearing. Because the XAG04Z is a high-RPM tool, even a deviation of 0.5mm in the shaft's axis creates significant centrifugal force, resulting in the "wobble" you see. This is most commonly caused by "side-loading," where the tool is tilted during a heavy grind, or by dropping the tool while a disc is mounted, which leverages the disc's diameter to bend the shaft. To confirm the root cause, remove the locking nut and the grinding disc entirely. Spin the bare spindle by hand while focusing your eye on the very tip of the threaded shaft. If the tip of the shaft moves in a circular or elliptical motion rather than staying centered on a single axis, the shaft is physically bent. If the shaft looks straight but "chatters" or feels gritty when spun, the internal ball bearings have developed flat spots or the race is pitted, causing the shaft to sit off-center during rotation.

How to Fix It

Since the XAG04Z uses a press-fit assembly, you cannot simply "straighten" the shaft; it must be replaced. Because the spindle is integrated into the gear housing, the most reliable fix is replacing the gear head assembly.

1. Disconnect the 18V LXT battery immediately to prevent accidental trigger activation.
2. Remove the four M4 hex screws securing the gear housing to the main motor chassis.
3. Carefully pull the gear head assembly away from the motor armature. Note the orientation of the drive gear to ensure it aligns perfectly upon reassembly.
4. Use a hydraulic press or a heavy-duty bench vise with a socket that matches the shaft diameter to press the damaged spindle out of the gear housing.
5. Clean the bearing seat with a lint-free cloth and a small amount of degreaser to remove any metal shavings.
6. Press in a new replacement output shaft (Part No. 904320-11 or equivalent for the XAG04Z model). Ensure the shaft is seated flush against the internal gear.
7. Apply a small amount of high-temperature lithium grease to the gear teeth before sliding the gear head back onto the motor armature.
8. Reinstall the four M4 screws, tightening them in a cross-pattern to ensure even pressure across the housing.

If That Didn't Work

• Check the Flange Washer. If the inner flange (the part that sits between the shaft and the disc) is warped or has a burr on the mating surface, the disc will sit tilted even if the shaft is straight. Replace the flange washer if it is not perfectly flat.
• Inspect the Locking Nut threads. If the threads on the nut are stripped or flattened, the nut may feel "tight" but isn't actually clamping the disc against the flange, allowing the disc to shift side-to-side during rotation.
• Examine the Motor Armature. In rare cases, the wobble is not in the spindle but in the motor's drive shaft. If the motor itself is vibrating violently, the armature may be unbalanced or the motor bearings may have failed, mimicking a spindle wobble.
• Verify Disc Compatibility. Ensure you are using a disc specifically rated for the XAG04Z's maximum RPM. Using an oversized or low-quality disc with inconsistent thickness can create an optical illusion of a bent shaft due to imbalance.

Heads Up

• Never use a hammer directly on the spindle shaft to loosen a stuck nut; always use the spindle lock button and a proper flange wrench to avoid bending the shaft.
• Avoid "side-grinding" or applying lateral pressure to the tool; the XAG04Z is designed for perpendicular cuts and surface grinding.
• Periodically clean the spindle threads with a wire brush to prevent debris from creating an uneven seat for the locking nut.
• If you experience excessive vibration, stop immediately. Running a tool with a bent shaft can destroy the motor bearings and potentially cause the disc to shatter.