A lawn mower can begin vibrating so severely it seems like the mower is going to fall apart. To have a good mowing experience, you need to identify the cause of the vibration and get your mower working right.

Performing routine service on your Craftsman mower can help identify and prevent components from causing vibration.

A Craftsman lawn mower may experience vibration from loose hardware on the mower; bad bearings in the pulleys and spindle housings; debris lodged in the mower; worn parts; and incorrect or unbalanced mower blades.

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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 Craftsman Lawn Mower is Vibrating

Take Safety Precautions to Prevent Craftsman Mower from Starting 

It is important to take safety precautions before working on your mower. These precautions include parking your Craftsman on a level surface and set the parking brake. Remove the ignition key and disconnect the spark plug wire(s). Wear good work gloves to protect your hands from sharp blades.

These steps need to be taken to prevent your mower from moving and starting while troubleshooting your Craftsman mower. Consult your operator’s manual for additional safety tips specific to your Craftsman model.

Check Engine Mounting Bolts on Your Craftsman 

On engines in all Craftsman mowers, you will find mounting bolts placed under the engine. These mounting bolts, also known as motor mounts, are used to absorb much of the vibration coming from the engine while it is running.

Take a look at the bolt to make sure they are secure and not broken or worn. You must replace mounting bolts as needed to keep them secure and in good condition.

If you own a Craftsman push mower, you will need to look at the engine mounting bolts when excessive vibration is felt after you engage the mower blade.

Check the Clutch on Your Craftsman 

You will find an electric or manual engagement clutch in your Craftsman lawn mower unless you are using a push mower.

You may feel a vibration when a ball bearing fails in an electric clutch or the engagement linkage, bushings and linkages fail in a manual engagement clutch. A manual clutch is one that is used with belts and pulleys.

A clutch is not used on a push mower. A push mower uses a lever to engage the blade. You should check this lever for worn or loose components.

Inspect Your Craftsman Mower Blades 

When the wrong blades are installed or the correct blades are installed incorrectly, a vibration may be created that is felt throughout the mower. You must use the correct size blades with the correct center hole size.

Correctly Sized Craftsman Blades

If you are using aftermarket mower blades on your Craftsman, make sure they fit your mower correctly. I have found some mower blades that list the correct center hole and blade length size actually don’t fit correctly.

The best way to verify this is by physically matching an aftermarket blade to an OEM blade if you choose to use aftermarket blades.

Craftsman Blade Hardware Installed Correctly

Refer to a parts diagram or your owner’s manual to confirm you are using the right hardware to secure your blade. This hardware must be installed in the order shown in the diagram.

When the mower blade isn’t secured correctly, you can experience movement in your blade that can cause your Craftsman to shake.

Craftsman Blade is Balanced

An unbalanced blade will not spin the blade evenly and leveled because one side of the blade is heavier than the other. The uneven weight distribution of the Craftsman blade can cause vibration and spindle bearing damage.

When the blade spins at high speeds, a significant vibration will be felt through your Craftsman mower.

Blades can become unbalanced when dirt that is sucked into the deck, from normal usage, wears one side of the blade more than the other. A blade can also become unbalanced during the blade sharpening process because 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 on your Craftsman. Learn more about sharpening and balancing your Craftsman blades here.

Check for Foreign Material Around Blade Shaft 

You take precautions to make sure you remove all objects from your yard before mowing so you don’t damage a blade or cause damage to your mower.

Even after taking these precautions, you still can pick up items that can get stuck under your mower deck and wrapped around your Craftsman blade shaft causing it to vibrate.

Small, thin, and hard-to-find objects like wire, string, or even long weeds can become wrapped around the blade shaft, as known as the blade spindle.

Inspect the blade shafts and remove any objects you find. Check the blade shafts and spindle housings for additional damage when you find material wrapped around the shafts.

Check for Bad Bearings in your Craftsman Spindle Housing 

When the bearings go bad in your spindle housings, you will feel movement in the blades. This small movement becomes more pronounced when the mower deck is engaged and the blades begin spinning at high speeds. This extra movement will cause your Craftsman mower to vibrate.

To check for a bad bearing in your spindle housing, make sure you are wearing a good pair of gloves and grab a hold of each side of your mower blade.

Rock the blade up and down to check for movement. Listen for a knocking sound as well. If you feel movement or hear this noise, you must remove your spindle housing and check the bearing.

Some models allow you to change out the bearing. You may find your Craftsman model only allows you to change the complete spindle housing assembly.

Check Your Craftsman Deck Belt and Pulleys

Move on to checking your Craftsman belt and pulleys. Damaged or worn pulleys or belts can cause your mower to shake. Replace your mower belt if it has a glazed appearance or has been stretched.

You will also need to replace your belt if you find signs of cracking or shredding on the belt. Check out my article on replacing a Craftsman deck belt for help.

Your vibration can come from a belt that isn’t sitting securely on the pulleys. When a pulley isn’t sitting level and parallel to the mower deck, a vibration can be felt when the belt runs along the pulley.

Check for a bad bearing in a pulley. A bad bearing can cause your pulley to not sit securely on your deck.

Rotate each pulley by hand to make sure it turns smoothly. When you feel a restriction or hear a bearing noise when turning the pulley, you must replace it.

Check Your Craftsman Idler Bracket & Spring

A loose idler bracket and spring can make your Craftsman 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 Craftsman Mower 

When mowing your lawn, your Craftsman kicks up a lot of debris that can collect on your mower deck.  If you don’t remove your belt covers (if your mower uses them) and clean off the top of your mower deck frequently, debris can collect under your pulleys.

This can cause the pulleys to not sit flat and parallel to the deck and send a vibration through the deck as the belt runs around the pulley.

Even the smallest little items can cause your Craftsman mower to start shaking. Look every part of your mower over carefully and remove any items that are lodged in your mower.

It is best to clean your Craftsman after each mowing to keep it in good condition. Need help with cleaning procedures? Check out “How to Clean Your Mower for Best Performance“.