The Best Method For Replacing Your Lawn Mower Deck Spindle

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When you begin seeing an uneven, ragged cut while mowing your lawn, you may take it as a sign it's time to sharpen mower blades. If your mower deck is vibrating, you may think you need to balance your mower blades. Should you hear clunking, grinding, squealing, or other strange noises, it may lead you to believe it's time to replace your lawn mower. While any of those could be the case, there is another possibility: You may need to replace your lawn mower deck spindle. While replacing the spindle itself is one possibility, while you're at it, it's typically best to replace the entire deck spindle assembly. This actually is quicker and simpler to accomplish and can prevent future issues, saving your both time and money in the long run.

In simplest terms, a lawn mower deck spindle (also called a mandrel) is a cylindrical metal shaft. Its importance lies in its function, which is to spin the mower blades. The mower blade is connected to the spindle beneath the deck. The spindle housing, bearings, and pulley make up the rest of the components of the spindle assembly. The spindle itself can become bent or damaged, often by hitting an object such as a rock or tree root. However, any of the parts in the spindle assembly can also become damaged or worn out and cause problems, such as uneven cutting or excessive vibration.

It is entirely possible to remove just the spindle shaft from the other components and replace it, should it be the offending part. However, this is typically much more labor-intensive than replacing the entire assembly. Additionally, if any of the other parts are worn or even slightly damaged, you may find yourself having to go through the repair process again sooner rather than later. 

Replacing the mower deck spindle assembly is a relatively easy task and can typically be accomplished in under an hour. First, buy a new spindle assembly, matching the make and model of mower. Many assemblies, such as the Monkemon spindle assembly for Husqvarna and Craftsman, can be purchased as a single unit or in multi-unit packs. You will also need a handful of tools, including pliers, a screwdriver, socket set, and grease gun. If the bolts are rusted or corroded, an impact wrench can help break them loose.

Once you have your tools and supplies, position the mower on a solid, flat surface and disconnect the power source for safety. Remove your mower deck, lay it upside down, and remove the blade just as you would to sharpen it. Next, turn the deck over again and clear the belt from the pulleys. Remove the bolt holding the pulley in place and take off the pulley. Finally, remove the bolts holding the spindle assembly in place and take it out through the bottom of the mower deck.

After removing the old one, clean the mower deck, then put the new spindle assembly in place, inserting it through the bottom of the mower deck. Make sure the mounting holes are aligned and secure the assembly in place with mounting bolts. Next, put the pulley on the new assembly, lacing the belt through before securing the pulley with the bolt. It's worth greasing the assembly at this point, even if it came pre-lubed. Turn the deck over and replace the mower blade. As an aside, it's a good idea to go ahead and sharpen your mower blade by hand while you have it off. Finally, reinstall the deck on your mower.

The spindle assembly on most of the best lawn mower models will provide hassle-free service for 5 years or more. Mower spindle assemblies can go out much sooner due to excessive wear, poor maintenance, or blunt impact from hitting objects, but a well-maintained assembly can last a decade. Given that many of the signs of a damaged spindle assembly can also be symptoms of damage to other mower parts, you shouldn't automatically assume your spindle assembly is bad. It's better to check the health of your spindle before replacing, otherwise you may make a repair that doesn't address the actual issue.

To check if your spindle assembly is indeed the problem, start by removing the spark plug or disconnecting the power source. Then, raise the mower deck as high as possible or tilt the mower on its side and thoroughly inspect the top and bottom of the spindle assembly. With this visual inspection, you are looking for any cracks, chips, bends, or breaks in any component of the assembly, including the pulley. Next, try to move the blade up-and-down and side-to-side. If there is any wobble, odds are your assembly is bad. If everything is snug, there may be another issue. Finally, make sure the belt is in good shape.

Regardless of whether it is the original spindle assembly or one you just installed, proper maintenance can help ensure it is long lived. This includes keeping the mower deck clean and removing any grass and debris from the blade and spindle after each mowing session. You should also grease the spindle assembly regularly to make sure the bearings remain in good working order and regularly inspect all parts for any damage or wear.