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Hammer Drill Repair – Replacing the Gear Assembly (Makita Part # 126460-9)


The gear assembly is an important component of your cordless drill. It consists of the transmission, the clutch, and the hammer drill mechanism. There are several symptoms that would indicate your gear assembly is going bad. The most common is that the motor spins, but the chuck does not. This is usually accompanied by a grinding sound from the transmission. It can occur in either the high or low gears. Or both at the same time. Be careful with this one though. Because, if the gear selector is accidentally moved between the high and low gears… your drill will display the same symptoms. Another symptom, is a clutch that is weak; or slips too easily. This is caused by wear to the clutch portion of the gear assembly. Replacing the gear assembly will solve this problem. The hammer drill function is part of the gear assembly as well. If your drill will no longer hammer when you need to drill masonry or concrete, You will need to replace the gear assembly. Hi, I’m Mark Sodja. Do-it-yourself repairs like these are easier than you might think. From lawn machines to cordless drills… …kitchen mixers… …outdoor grills… Our “how-to” videos walk you through each repair from start to finish. So, doing it yourself means never having to do it alone. Let’s get started. We’ll begin by removing the chuck. I’ll open the chuck as wide as it will go. There’s a retaining screw on the inside of the chuck that I need to remove. That screw is a reverse-thread. So, I’ll turn the screwdriver clockwise to remove it. With the screw out of the way, now I can remove the chuck. To do that, I’ll use a large Allen wrench. I’ll chuck it into the chuck; just like I would a drill bit. Then I’ll rotate it around Until it extends out past the drill. Now I can use this as a lever to strike with a hammer The quick burst from the hammer will break the chuck free and allow me to unscrew it. Now I’ll remove the battery. Now I’ll remove the rear cover. It’s secured with two screws. Now I’ll remove the housing. Now I’ll release the heat sink away from the motor. And rock the gear assembly upwards slightly. And I can pull it away from the motor. You want to be careful with the gear selector. There’s a couple springs on the back side, you don’t want to lose. Now I can install our new gear assembly. First, I’ll go ahead and place the gear selector back onto the gear assembly. It fits over this little post. Those springs just go right around either side of the post. Now I’ll line up the gear on the motor with the gears on the gear assembly. Press the two together. And now place the gear assembly back into the motor housings. Take your time to line everything up. There’s a notch on the back side of the field that will lock back into the housing. And I’ll push the heat sink back into place as well. With the new gear assembly in place, I can go ahead and replace the housing. Now I can replace the rear cover. Before I put it in place on the drill, I want to check the brush springs. And make sure that they’re still in place while we had the gear box out. Everything looks good, so I’ll press the cover on and secure it with the two screws. I’ll screw the chuck back onto the spindle. Open the chuck back up. And replace the retaining screw. And again remember; that is a reverse thread. So, counterclockwise to tighten. Be sure to check back often for new videos and expert advice. If you found this video helpful, give us a thumbs-up. And leave a comment.

Bernard Jenkins

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