the spindle lock on my xag04z won't engage, button feels mushy and the shaft just spins freely.

Diagnosis

The "mushy" feeling in the spindle lock button of the Makita XAG04Z typically indicates a mechanical failure within the locking pawl assembly. In a healthy unit, the button pushes a spring-loaded steel pawl directly into a notch on the spindle shaft. When the button feels soft and the shaft continues to spin, it means the pawl is no longer making physical contact with the spindle, or the internal return spring has collapsed or snapped. This failure is usually caused by one of two things: the accumulation of metallic "swarf" (fine metal dust and grinding debris) that has packed into the lock housing, preventing the pawl from extending fully, or a sheared pivot pin. Because angle grinders operate at high RPMs, any slight misalignment during a disc change can put lateral pressure on the lock, eventually wearing down the engagement edge of the pawl until it simply slips over the spindle notch rather than locking into it. You can confirm this by removing the accessory and attempting to engage the lock; if the button travels further than usual without a hard "stop," the internal linkage is compromised.

How to Fix It

To resolve this, you must access the internal locking mechanism to clear debris or replace the worn components. Follow these steps precisely:

1. Disconnect the 18V LXT battery immediately to prevent accidental trigger engagement.
2. Remove the wheel guard by loosening the mounting screw and sliding the guard off the gear housing.
3. Unscrew the flange nut from the spindle using the provided pin wrench.
4. Using a precision needle-nose pick or a small flat-head jeweler's screwdriver, carefully pry the rubberized protective boot away from the spindle lock button.
5. Locate the small retaining screw securing the metal button plate. Use a PH1 precision screwdriver to remove this screw.
6. Lift the button plate assembly. Inspect the small steel pawl and the tension spring. If the spring is kinked or missing, the button will feel mushy.
7. Use compressed air or a shop vacuum to suck out all metallic shavings and grit from the cavity. If the pawl is stuck, use a small amount of electronic contact cleaner to dissolve any solidified grease.
8. Inspect the tip of the pawl for rounding or cracks. If the metal is worn smooth, the pawl will not grip the spindle notch.
9. If the pawl is damaged, replace the entire lock assembly (Part No. 463642-1). Slide the new assembly into the housing, ensuring the pawl aligns perfectly with the spindle notch.
10. Reinstall the button plate, tighten the retaining screw, and snap the rubber boot back into place.

If That Didn't Work

• Check for Spindle Scoring: If the lock assembly is new but still slips, inspect the notch on the spindle shaft itself. If the notch has been "rounded off" due to previous forced disc removals, the pawl has nothing to grip. In this case, the entire spindle assembly must be replaced.
• Verify Button Alignment: Ensure the button plate isn't bent. If the metal plate is slightly warped, it can create friction against the housing, making the button feel mushy even if the pawl is functional. File down any burrs on the plate edges.
• Lubricate the Pivot: Apply a single drop of high-temperature synthetic grease to the pawl pivot pin. Over-lubricating is dangerous as it attracts metal dust, but a dry pivot can cause the pawl to hang up and fail to engage fully.
• Inspect for Housing Deformation: Check if the gear housing has any dents near the lock button. Even a slight crush in the aluminum housing can shift the lock axis by a fraction of a millimeter, preventing the pawl from seating.

Heads Up

• Avoid Over-Tightening: Never use the spindle lock to "torque" a disc on. Use the lock only to hold the shaft while you start the nut; finish tightening the nut by hand or with a wrench while the tool is off.
• Clean Regularly: Use compressed air to blow out the spindle lock button every 10-15 discs. Metal dust is conductive and abrasive; it will destroy the spring tension over time.
• Disc Compatibility: Ensure you are using genuine 4-1/2" discs. Using oversized or off-brand discs can put uneven pressure on the flange, which stresses the spindle lock mechanism during changes.
• Battery Safety: Always remove the LXT battery before performing any maintenance on the spindle or gear head to avoid catastrophic accidental starts.