How to Replace the Rear Armature Bearing on a Makita Grinder

Armature bearings grinding on your nerves? It's time to face the fix. Whether you are a master mechanic or a garage-based grinder, eReplacementParts.com provides the parts, procedures and facts you need to fearlessly fix what fails you.

Your grinder's armature has two bearings: one on the front, and one on the rear. Over time, these bearings can deteriorate. Symptoms of ailing armature bearings may include squealing, screeching, and an entirely different type of “grinding” (usually heard or felt as the motor powers-down). Fortunately, rear armature bearings are very easy to replace — especially if problems are detected early.

This article will show you how to remove and install the rear armature bearing on Makita grinder.

Let's get started.   REMOVING THE REAR BEARING [top] 1. Remove the side handle.

Unscrew and remove the side handle from the grinder.

  2. Remove the guard.

Loosen the lock-screw on the guard assembly.

Rotate the guard assembly to disengage it from the housing.

Remove the guard from the grinder.

  3. Remove the gear housing.

Remove the (4) screws from the gear housing.

Separate the gear housing from the motor housing.

  4. Remove the rear cover.

Remove the (1) screw from the rear cover.

Slide the rear cover away from the motor housing.

  5. Disengage the motor brushes.

Use a pick to (gently) lift the brush spring from the back of the carbon motor brush.

Reposition the brush spring alongside the motor brush (against the brush holder).

Pull (gently) on the wire lead to disengage the motor brush from the armature.

Repeat this step to disengage the second motor brush.

  6. Remove the armature assembly.

Slide the armature assembly (which is attached to the gear housing cover) out of the motor housing.

  7. Remove the rear bearing.

Remove the rubber ring from the rear bearing.

Position the bearing separator beneath the rear bearing.

Tighten the bearing separator bolts.

Place the bearing separator (and armature assembly) in the vise. The jaws of the vise should be opened wide enough to accommodate the armature (without touching it).

Use a punch and a hammer to tap the end of the armature shaft until the bearing breaks free from the spindle.

Remove the rear bearing from the armature.

  INSTALLING THE NEW REAR BEARING [top] 8. Install the rear bearing.

Slide the new bearing onto the armature shaft.

Locate a socket that has the same diameter as the inner race of the new bearing.

Position the socket squarely against the bearing.

Tap the socket with a hammer to press the bearing on the armature shaft.

Continue tapping the socket until the bearing is fully seated on the armature.

  REASSEMBLING THE UNIT [top] 9. Reinstall the armature assembly into the motor housing.

Reinstall the rubber ring onto the rear bearing.

Slide the armature assembly into the motor housing.

Align the gear housing cover with the motor housing.

  10. Reinstall the gear housing.

Install the gear housing onto the grinder (aligning the mounting holes with the gear housing cover and the motor housing).

Secure the gear housing to the grinder with the (4) screws.

  11. Re-engage the motor brushes.

Use a pick to (gently) lift the brush spring away from the brush holder.

Position the brush spring against the motor brush.

Repeat this step to engage the second motor brush.

  12. Reinstall the rear cover.

Visually inspect the wires for potential “pinch-points” and adjust/tuck the wires as necessary.

Slide the rear cover onto the motor housing.

Secure the rear cover with the screw.

  13. Reinstall the guard.

Install the guard assembly onto the grinder.

Rotate the guard assembly to engage the mounting plate.

Secure the guard with the (1) screw.

  14. Reinstall the side handle.

Install the side handle onto the grinder.

Tighten the side handle until secure.

You can't place a value on a job well done, unless you did it yourself. (Which you did.) Now you can place that value back into your own pocket. (Or into your business.) Not only did you refine your grinder at a fraction of the cost of replacement; you have expanded your skills far beyond the daily grind.

Find your next grind here.   [top]