What Causes A Mower Deck To Vibrate (8 Basic Reasons)

After a long time of use, your lawn mower may experience various problems such as noise, vibration mower deck, weak motor, damaged power cord, etc.

One of the common problems that you will encounter is the condition of the lawn mower deck shaking violently. What causes a mower deck to vibrate? Some of the underlying causes are damaged or unbalanced blades, worn belts or pulleys, damaged crankshafts, dirt, or small debris trapped in the pulley or spindle. To learn more about the causes and how to fix this situation, let’s find out more information in the article below.

What Causes A Mower Deck To Vibrate – Here Are 8 Main Causes

Before figuring out what causes the deck of your lawn mower to shake, you need to make sure it’s safe by removing the key and turning off the engine. Also, unplug the spark plugs to prevent the lawn mower from starting while you’re working on the deck. Here are 8 main causes of lawn mower decks shaking violently while in operation.

A Broken Or Unbalanced Blade

One of the main causes of a lawn mower deck shaking is the blade. Damaged, unbalanced, worn, or lost blades due to impact with solid objects during mowing will cause the deck of the lawn mower to vibrate.

During the lawn mower’s work, and is also the cause of the blade’s wear. In addition, improperly sharpening the blade and causing the edges to wear will also cause the deck of the lawn mower to become unbalanced.

When sharpening a lawn mower blade, you need to sharpen both sides of the blade to create balance. You can use a blade leveler to ensure that the two sides of the blade are sharpened in equal proportions.

What causes a mower deck to vibrate

The blade Is Installed In The Wrong Position Or Improperly

Recently, if you replace the blade with a new one and the lawn mower shakes while working, you should check the position of the blade. You need to make sure the blade is installed correctly and the type is right for your lawn mower.

As you know, not all blades are the same. Different types of lawnmowers will need different types of blades. Therefore, you need to learn and choose the correct blade types.

The length of the blade and the size of the center of the blade are the two most important factors when choosing a blade. If you do not know the exact specifications of the cutting mesh, you can compare the two blades by placing them on top of each other to observe.

When installing blades, you should ensure that the blades are fitted with the sail or the high side of the blade facing the deck. If you put the blade of the lawn mower upside down, it will not be able to cut the grass, but it will crush the grass.

The Shaft Of The Blade Is Covered With Foreign Matter

In the process of mowing, it is difficult to completely avoid foreign objects on the lawn. A few common objects such as ropes, long grass, or rubber bands. They will wrap around the shaft of the blade and prevent the blade from working as it should. Therefore, you need to completely remove foreign objects, rubber bands, or solid objects from the shaft of the blade to avoid damage.

The Bearing In The Main Shaft Housing Is Damaged

You need to check the bearing in the main shaft housing of the lawn mower for damage. The severely damaged bearing will affect the balance and cause the deck of the lawn mower to shake violently. When inspecting the spindle bearing, you should use a pair of protective gloves because you may be injured by the sharp blades. Grasp the ends of the blade to see if they move. If the blade moves or vibrates, you should replace the bearing with a new one.

Here are some steps to repair a damaged bearing:

  • Remove the belt from the pulley: Use a special tool or an object to pry the belt off the pulley.
  • Remove the pulley: Use the tool to insert the nut of the pulley and remove it. Depending on the type of lawn mower, the pulley can be fixed with screws or without screws. They can be Allen screws or hexagon screws. These screws are not easy to remove, so you need to use special tools to remove them.
  • Remove the spindle: You will need 4 to 8 bolts holding the spindle in place. Remove the bolts and the assembly will fall off the bottom of the deck.
  • Replace a new bearing: You will replace the bearing with a new one by oiling it. Then attach it to the deck in the reverse of the steps you took off.
  • Reassemble the housing, pulley, and belt: After you’ve screwed the deck and installed the pulley. Make sure that every part is tight and free of any movement. Then you proceed to reinstall the belt. You should rotate the belt by hand to ensure that it rests on all pulleys. 

Loose Belts And Pulleys

Cracked, worn or loose belts will also cause the deck of the lawn mower to vibrate during operation. You should replace the belts with new ones if they are broken, worn, or loose.

You should check the tensioner pulley and tensioner arm regularly. Make sure that they are working properly to keep the tension in the belt. Also, you should oil the tensioner arm so it doesn’t get stuck.

Don’t forget to check the pulley of the lawn mower deck. Use your hands to check each pulley, turning them slowly to check resistance. If the pulley does not rotate smoothly or makes strange noises, you should replace the pulley to ensure the operation of the rotating shaft.

Hard Debris In The Deck Of The Lawn Mower

The smallest debris if they accumulate in the deck of the lawn mower will also cause the deck to shake. Debris such as iron chips, wood chips, acorns, pinecones, stones, gravel, sticks, etc. can all get stuck in the deck of the lawn mower.

Debris can make strange noises when the lawn mower is working. Or rub against the pulley causing the lawn mower to vibrate. You should regularly clean to remove dirt, small debris, or foreign objects in the deck of the lawn mower.

Damaged Crankshaft On A Push Mower

When the blade hits a hard object, it will be unbalanced. Meanwhile, the crankshaft will bend in a push mower. If you suspect the cause of the lawn mower shaking is due to the rotating shaft, you should seek professional help. Because you may be in danger if you check the spindle operation yourself on a push mower.


There are many causes for the deck of a lawn mower to shake while working. Some of the basic causes such as broken or unbalanced blades, foreign matter covering the spindle or pulley, damaged bearings, etc.

As soon as you notice the lawn mower is shaking violently, turn it off, turn off the engine, and unplug it before taking any action. Use protective gloves and carefully inspect the parts involved with the blade as you may be injured.

For the lawn mower not to vibrate abnormally, you should periodically check the parts, lubricate, and remove dirt, and debris in the spindle and pulley. From there, the lawn mower will limit debris and cause damage to the rotating shaft.

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