There are times when your riding mower can begin vibrating so badly it can feel like you are going to shake right out of the seat. It can be surprising when you find the actual cause of the vibration.

It can be something as little as a wood chip lodged in your riding mower. Because such little things can be the cause of your shaking, it can be difficult to know just where to start troubleshooting your problem.

A riding mower may begin vibrating when engine mounting bolts and hardware become loose or worn. A bad clutch, worn mower blades, stretched deck belt and bad bearing in the spindles and pulleys can cause a vibration in your riding mower.

Look for foreign objects lodged in your mower and deck in addition to worn bushings and linkages. Keep reading for a complete list of items you need to check out when looking for a vibration.

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Follow all safety instructions provided in your equipment operator’s manual prior to diagnosing, repairing, or operating.Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.

Troubleshoot Why Your Riding Mower is Vibrating

Take Safety Precautions Before Working on Your Riding Mower

Before you begin working on your riding lawn mower, it’s necessary to take safety precautions to prevent your mower from moving and starting while you are working on it. Take these steps before you start the troubleshooting steps.

• Park your riding mower on a flat-level surface. Set the brake. Use wood chocks as added security to prevent your mower from moving.
• Remove the ignition key and disconnect the spark plug boots to prevent your mower from starting.
• Wear thick work gloves while working with your sharp blades. In addition, wear safety glasses to prevent getting debris in your eyes.
• When raising your mower to gain access to your deck, make sure it is lifted securely in the air with jacks if it is possible to do so. You may have to remove the deck on your riding mower.
• Consult your owner’s manual for additional safety steps that need to be taken with your specific model riding mower.

Check Engine Mounting Bolts on Your Riding Mower

Manufacturers place engine bolts, sometimes referred to as motor mounts, under the engine. These bolts are used to absorb vibration when your mower’s engine is running. If these bolts are broken, worn, or missing, they must be replaced.

Check the Clutch on Your Riding Mower

You may find your riding mower has a manual engagement clutch. This is a clutch that is used with a belt and pulleys. The bushings and linkages on these types of clutches can fail and cause a vibration.

If your mower doesn’t have a manual clutch, it will have an electric clutch. When the ball bearing fails in this type of clutch, it can begin vibrating.

Inspect Your Riding Mower Blades 

Mower blades are often the cause of your mower’s vibration. When the blades are incorrect, not installed right, or unbalanced, they can wobble with every rotation creating an excessive vibration when the deck is engaged.

Correctly Sized Riding Mower Blades

I like to use OEM (Original Equipment Manufacturer) blades on my mower to ensure I am using the correct blades. If you choose to use aftermarket blades, having the blade length and center hole size will help you select the right blade.

While these measurements give you a good chance of getting a blade that will fit your riding mower, it doesn’t always happen.

If you purchase an aftermarket blade, match it up to an OEM to make sure it’s a match. I have seen some aftermarket blades where the manufacturer states a certain blade length and center hole size, but it actually did not fit.

Sometimes you just need to change aftermarket manufacturers to find one that fits correctly.

Riding Mower Blade Hardware Installed Correctly

You must use the correct hardware for your model mower deck. This hardware needs to be installed correctly in the right order.

Refer to your owner’s manual for installation instructions and a diagram showing the correct placement of your hardware. You can also refer to a parts diagram. Incorrect hardware or installation of the hardware can cause a vibration.

Riding Mower Blade is Balanced

An unbalanced blade, where one side of the blade is heavier than the other, can cause your riding mower deck to vibrate. Not only can an unbalanced blade create a vibration, but it can also cause spindle bearing damage magnifying the vibration problem.

Blades can become unbalanced when the dirt is sucked into the deck and cause uneven wearing of the mower blade. It can also become unbalanced during the blade sharpening process. This happens when more metal is removed from one side of the blade than the other.

It’s important to balance your blade using a blade balancer after you sharpen your blades and before installing it on your riding mower. Learn more about sharpening and balancing your riding mower blades here.

Check for Foreign Material Around Blade Shaft 

While walking your yard to remove any obstacles before you mow can minimize damage to your riding mower, you can still run over items that can cause damage and vibration to your mower. You could miss a thin piece of wire or string that can wrap itself around your blade shaft.

Even a long weed can get caught in the blade shaft and wrap itself around it. Check the blade shaft. If you find a foreign item wrapped around the shaft, check your spindle housings for additional damage. Use the steps in the next step to check your spindle housings.

Check for Bad Bearings in your Riding Mower Spindle Housing 

Bearings in your spindle housings can go bad allowing movement in the blade. To check for bearing damage, grab both ends of a mower blade and rock it up and down.

Listen for a knocking noise and feel for excessive play or movement. (This is the step you need to make sure you are wearing gloves to protect your hands).

If you notice the blade isn’t secure and there is movement or knocking, remove your spindle housing and inspect the bearing for damage. Repair your spindle housing by replacing the bearing.

On some mower decks, you don’t have the option to replace the bearing. You will have to replace the spindle assembly.

Check Your Riding Mower Deck Belt and Pulleys

Loose and worn belts and pulleys can cause your riding mower to vibrate. The slack in a stretched belt can cause your problem. Sometimes your belt is in good condition, but it is still causing your shaking problem when it runs around a pulley with a bad bearing.

A pulley with a bad bearing may not sit level and parallel to the deck. There can be extra movement in the pulley which is felt when the belt rotates around the pulley.

Check the condition of each pulley by slowly rotating it by hand. Replace any pulleys where you feel a restriction, hear a bearing noise, or it doesn’t sit securely on the mower deck.

A deck belt needs to be replaced when it shows signs of wearing including cracking, shredding, and a shiny glazed appearance.

Check Your Riding Mower Idler Bracket & Spring

A loose idler bracket and spring can make your riding mower shake as well. The spring and the bracket can wear over time. These items will need to be replaced. You should also check the bearing and bushing in your engagement linkage and replace them if necessary.

Check for Debris Lodged in Your Riding Mower 

Mowing can be a dusty and dirty job. Your mower kicks up dirt, grass clippings, and other small items that can become lodged in your riding mower.

Check over every inch of your mower looking for an item that shouldn’t be there. A small piece of bark or a stone can get caught in your mower or under a pulley which can cause your mower to shake.

It’s important to regularly clean off your lawn mower after every mowing. I use a leaf blower to remove debris from my mower before I place it in my garage for next time. Check out “How to Clean Your Mower for Best Performance” for more information.