my bosch gbh2-28l just makes a whining noise and the chuck doesn't spin or hammer, what gives?

Diagnosis

The whining noise you are hearing is the armature and field coils of the motor spinning at full RPM, but the torque is not being transferred to the SDS-plus chuck. This indicates a mechanical disconnection between the motor's drive shaft and the striking mechanism. In the Bosch GBH2-28L, this is most frequently caused by the mode selector dial becoming misaligned or "floating" between positions. When the selector is not fully seated into a specific detent, the internal locking pin fails to engage the drive gear, leaving the motor to spin freely without engaging the hammer or rotation assembly. Alternatively, this symptom can point to a sheared drive gear or a failed planetary gear set. If the tool was used to apply excessive lateral pressure or if it suffered a hard drop, the internal teeth of the drive gear may have stripped. To confirm if it is a simple selector issue versus a catastrophic gear failure, listen closely to the pitch of the whine; a high-pitched, smooth whine usually suggests the selector is out of gear, whereas a grinding or rattling sound accompanying the whine suggests broken internal teeth.

How to Fix It

To resolve a selector misalignment and restore power to the chuck, follow these precise steps:

1. Disconnect the tool from the 120V power source immediately to prevent accidental activation.
2. Locate the mode selector dial on the side of the gear housing. Rotate the dial slowly through all three positions: 'Hammer Drill' (hammer icon), 'Drill Only' (drill bit icon), and 'Rotation Stop' (chisel icon).
3. Apply firm, deliberate pressure to ensure the dial "clicks" firmly into each detent. If the dial feels mushy or doesn't snap into place, use a small amount of compressed air to blow out any concrete dust or debris trapped in the selector crevices.
4. Once the dial is firmly seated in 'Hammer Drill' mode, grasp the chuck and attempt to rotate it by hand (while unplugged) to see if there is any mechanical resistance.
5. Plug the tool back in and trigger the switch. If the chuck now spins and hammers, the selector was simply misaligned.
6. If the tool still whines, rotate the dial to 'Rotation Stop' (chipping mode) and trigger the switch. If the tool hammers in this mode but won't rotate in others, the issue is specifically within the rotation gear assembly.

If That Didn't Work

• Inspect the Carbon Brushes: While a whining motor usually means brushes are making contact, worn-out brushes can cause "voltage drop" where the motor spins but lacks the torque to engage the heavy hammer mechanism. Remove the plastic brush caps on the side of the motor housing and ensure the carbon blocks are at least 1/4 inch long and the springs are applying constant pressure.
• Check for a Sheared Drive Pin: Open the gear housing by removing the perimeter screws. Inspect the drive pin that connects the motor armature to the gear train. If this pin has sheared off, the motor will spin the armature, but the gear train will remain stationary. This requires a full gear assembly replacement.
• Verify the Selector Cam: If the external dial turns but the internal cam is stripped, the tool will never engage. Check if the internal plastic teeth of the selector switch have worn down. If the cam is stripped, you will need to replace the mode selector assembly.
• Check for Grease Hardening: In extremely cold environments, the heavy-duty grease in the GBH2-28L can thicken to a point where the selector pin cannot slide into the gear. Let the tool warm up to room temperature or gently warm the gear housing with a heat gun on low setting to liquefy the lubricant.

Heads Up

• Avoid "Between-Mode" Triggering: Never pull the trigger while you are rotating the mode selector dial. This can shave the edges off the internal locking pins and lead to permanent selector failure.
• Lubrication Maintenance: Every 50-100 hours of heavy use, apply a small amount of high-temperature SDS-plus grease to the shank of your bits to reduce friction and wear on the internal chuck drive.
• Dust Management: Concrete dust is abrasive and can migrate into the selector switch. Periodically blow out the selector dial area with compressed air to prevent the "mushy" feeling that leads to misalignment.
• Avoid Overheating: If the motor begins to smell like burning ozone or the housing becomes hot to the touch, stop immediately. A whining motor that is overheating often indicates an internal mechanical bind that can burn out the armature.