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Grinder: Grinding or Squealing Sound

If you hear a grinding or squealing sound coming from your grinder, chances are, a repair is needed. Begin by inspecting these common parts for damage: the gears, bearing, armature, carbon brush, and spindle. Take on the repair project yourself, and read our tips for the most efficient and accurate way to get your tool back up and running. Refer to your owner's manual for detailed instruction for your model.

Bearings
Bearings
A worn out bearing will generate a noise, such as a rumbling, howling, grinding or growling sound and it can also have play in it, causing a vibration. To check and replace the bearings, remove the wheel cover and the handle. Remove the gear box assembly from the grinder. Take out the spindle assembly from the gear box assembly. Depending on your angle grinder, the next steps will vary as all makes and models are different.

Method #1: Remove the retaining ring securing the spindle gear and then the gear with the woodruff key. Once the gear is removed, there may be another retaining ring, or screws, securing a cover that holds the bearing in place, which will need to be removed to access the bearing. Once you have done so, clean out the grease then press out the bearing with your fingers. Install the new bearing by hand, evenly,...
A worn out bearing will generate a noise, such as a rumbling, howling, grinding or growling sound and it can also have play in it, causing a vibration. To check and replace the bearings, remove the wheel cover and the handle. Remove the gear box assembly from the grinder. Take out the spindle assembly from the gear box assembly. Depending on your angle grinder, the next steps will vary as all makes and models are different.

Method #1: Remove the retaining ring securing the spindle gear and then the gear with the woodruff key. Once the gear is removed, there may be another retaining ring, or screws, securing a cover that holds the bearing in place, which will need to be removed to access the bearing. Once you have done so, clean out the grease then press out the bearing with your fingers. Install the new bearing by hand, evenly, and pack with new grease. Reinstall the cover, or retaining ring, to hold down the bearing, and then install the woodruff key, with the spindle gear, and reinstall the retaining ring. Make sure the woodruff key stays in place during installation. Reinstall the spindle box assembly to the gear box assembly and then reinstall the gear box assembly to the grinder. Reinstall the wheel cover then reinstall the grinder wheel with flanges and secure with the lock nut.

Method #2: Use a bearing puller, or a separator, to remove the bearing on the spindle shaft. There may be a second bearing on the lower part of the spindle, depending on the model and therefore, you will have to remove the retaining ring and the spindle gear to access the lower bearing. Place the new bearing onto the shaft and use a socket that only makes contact with the inner bearing race to avoid damage. Use a hammer to tap it in place and then repack with new grease. Reinstall the spindle box assembly to the gear box assembly and then reinstall the gear box assembly to the grinder. Reattach the wheel cover and handle, followed by the grinder wheel, with flanges, and then secure the lock nut.

There are also two bearings located on the armature: one at the front and one at the rear. To replace a bearing on the armature, remove the gear housing from the grinder. Remove the lower cover and locate the brush holders. Move the tension springs to the side and pull the brushes out of the holders. For some models, the brushes are located on the side of the grinder, inside a cap. Remove these caps to remove the brushes. Remove the armature from the grinder and then the retaining ring, or nut, on the front of the armature. Now, remove the armature gear. Using a puller, or a bearing separator, remove the bearing.

Install the new bearing onto the shaft by using a socket that only makes contact with the inner race of the bearing to avoid damage. Use a hammer to take it in place. Reinstall the armature gear and the retaining ring or nut. For the rear armature bearing, remove it with a bearing puller, or separator, and the retaining ring or nut. For the rear armature bearing, remove it with a bearing puller, or separator, and then install the new bearing onto the shaft using a socket that only makes contact with the inner bearing race. Tap in place with a hammer. Slide the armature back into the grinder. Reassemble the gear housing to the grinder and then reinstall the carbon brushes. Next, reapply the tension springs onto the brushes and reinstall the lower cover.
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Gears
Gears
Gears with broken, or missing teeth, will make a grinding noise. To check the gears, remove the grinding wheel cover and the handle. The following procedure will vary slightly between all makes and models. Remove the gear box housing from the grinder and then remove the spindle box assembly from the gear box assembly. Inspect the gears for any signs of damage that will cause a grinding noise.

To replace the spindle gear, remove the bearing with a bearing separator or puller. Remove the retaining ring securing the woodruff key, making sure the woodruff key stays in place during installation. Reinstall the retaining ring and then the bearing with a socket that only makes contact with the bearings inner race to avoid damage. Tap it in place with a hammer.

To replace the armature gear, remove the retaining clip, or nut, holding the armature gear in place. Pull the gear...
Gears with broken, or missing teeth, will make a grinding noise. To check the gears, remove the grinding wheel cover and the handle. The following procedure will vary slightly between all makes and models. Remove the gear box housing from the grinder and then remove the spindle box assembly from the gear box assembly. Inspect the gears for any signs of damage that will cause a grinding noise.

To replace the spindle gear, remove the bearing with a bearing separator or puller. Remove the retaining ring securing the woodruff key, making sure the woodruff key stays in place during installation. Reinstall the retaining ring and then the bearing with a socket that only makes contact with the bearings inner race to avoid damage. Tap it in place with a hammer.

To replace the armature gear, remove the retaining clip, or nut, holding the armature gear in place. Pull the gear off and install the new armature gear and reinstall the retaining ring or nut. Reinstall the gear housing on to the grinder. Pack the spindle housing with fresh grease and reinstall the spindle housing back onto the gear box housing and then reinstall the gear box housing back to the grinder. Reinstall the grinding wheel cover and then the handle.
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Spindles
Spindles
The spindle is located inside the spindle box assembly. The spindle is threaded on one end in order to mount the grinding wheel. The other end houses the bearing and the spindle gear that transfers power from a 90-degree angle, of the armature gear. A worn, or damaged spindle may not seat properly anymore and it will be off alignment. This can cause noises from the spindle itself, and may cause the gears to be out of alignment, causing a grinding noise. The grinding wheels may have a wobble as well.

To replace a damaged spindle, remove the wheel cover and the handle. Remove the spindle box assembly from the gear box housing and then separate. Depending on your model, the bearing and gear placement may be in reversed positions on the spindle. Remove the spindle bearing using a bearing separator or a bearing puller. Take out the retaining ring,...
The spindle is located inside the spindle box assembly. The spindle is threaded on one end in order to mount the grinding wheel. The other end houses the bearing and the spindle gear that transfers power from a 90-degree angle, of the armature gear. A worn, or damaged spindle may not seat properly anymore and it will be off alignment. This can cause noises from the spindle itself, and may cause the gears to be out of alignment, causing a grinding noise. The grinding wheels may have a wobble as well.

To replace a damaged spindle, remove the wheel cover and the handle. Remove the spindle box assembly from the gear box housing and then separate. Depending on your model, the bearing and gear placement may be in reversed positions on the spindle. Remove the spindle bearing using a bearing separator or a bearing puller. Take out the retaining ring, wave washer – if there is one – and the spindle gear, with the woodruff key. Remove the spindle housing from the spindle and take out the labyrinth ring. Check the spindle to trueness by taking one gauge, held perpendicular, to the surface of the spindle and slowly move it across the surface of the part axially, as the part is rotated. If the gauge varies at any point by more than the total run-out tolerance, the part would be out of spec.

Install the parts in reverse order onto the new spindle. Make sure the woodruff key stays in place when installing the spindle gear. When installing the bearing, place a socket on top of the bearing that only makes contact with the inner race of the bearing to avoid damage. Now, tap it in place with a hammer and repack with grease. Reattach the spindle assembly box to the gear box housing. Install the wheel cover and handle back on the grinder.
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