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Your Simplicity Mower is Vibrating & Shaking (Make it Stop)

Mowing the lawn isn’t the smoothest task, especially if you have a lot of bumps in the lawn. The job can get a lot more uncomfortable when your mower begins to shake excessively. Let me try to help you solve your problem.

A Simplicity lawn mower vibrates and shakes when the engine mounting bolts are worn or missing, the clutch is going bad, the blades are unbalanced, the belt is worn, or debris is lodged in the mower.

It may also begin vibrating when the spindle, spindle housing bearing, or pulley bearing is bad, or the idler bracket or spring is worn.

Before working on your mower deck and performing any repairs, remove the ignition key and the spark plug boots. For more safety precautions, refer to your operator’s manual.

Simplicity mower is shaking

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Follow all safety instructions provided in your equipment operator’s manual before 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.

9 Reasons Why Your Simplicity Lawn Mower is Vibrating

1. Worn or Missing Engine Mounting Bolts

You’re always going to feel some vibration from the engine. However, the vibration from the engine can feel worse when the engine mounting bolts are worn or missing.

These bolts, sometimes referred to as motor mounts, are installed on the bottom of the engine to absorb vibration.

Inspect the bolts to ensure they are in good condition and securely in place. Tighten any loose bolts and replace bolts that are worn, broken, or missing.

If you own a push mower, check the engine bolts when you feel excessive vibration once you engage the mower blade.

2. Failing Clutch

On a lawn tractor, riding mower, or zero-turn, the ball bearing may fail on an electric clutch causing the mower to shake.

If your Simplicity mower uses a manual engagement clutch that uses belts and pulleys, the bushing and linkages can fail to cause a vibration.

A push mower does not use a clutch. It uses a lever to engage the blade. This lever needs to be checked for loose or worn components.

3. Incorrect or Unbalanced Mower Blades

Vibration can be created when the wrong blades are used or they are not balanced.

Wrong size mower blades:

Not every mower blade that has the correct center hole size and blade length will fit your lawn mower. I prefer using OEM (Original Equipment Manufacturer) blades so I know I’m running a good quality mower blade with the correct dimensions.

If you choose to use an aftermarket lawn mower blade, I recommend first laying it on top of an OEM blade to make sure it is a match before placing it on your mower.

Unbalanced mower blades:

Blades can become unbalanced and no longer spin evenly under the deck. They will begin to wobble as they spin. At very high speeds, you will feel a significant vibration.

An unbalanced blade is a blade that is heavier on one side (right or left side) of the blade than the other. There are a couple of different items that cause a mower blade to become unbalanced.

  • From Normal Use: Dirt rotating under the mower deck can wear the blades unevenly.
  • From Blade Sharpening: Too much metal is removed from one side of the blade than the other.

Make sure your blades are balanced using a blade balancer before you install blades on your mower.

If you don’t have a blade balancer, placing the center hole of the blade over a nail hanging off the wall can help you determine whether the blade is balanced.

You must remove metal from the blade that side of the blade that hangs lower until both sides sit level on the nail.

4. Material Wrapped Around the Blade Spindle

Wire, string, and even long weeds can wrap around the blade spindle causing your Simplicity mower to start vibrating. These are hard items to see when you’re mowing so they are hard to avoid.

Inspect the spindle and remove any items that are wrapped around it. Once this is done, check your spindle and spindle housing for further damage.

5. Damaged Spindle Housing Components

A bent spindle or worn bearings in the spindle housings on a riding mower or zero-turn can cause the blades to wobble when you engage the blades. This can cause vibration in your mower deck.

Before you check your spindle housing for damage, put on a good pair of work gloves to protect your hands from the sharp edges of the mower blade.

Grab a hold of each end of the blade and rock it up and down. What you’re doing is looking for any movement. You may hear a knocking sound from the extra movement.

If you feel movement, remove your mower blade and spindle housing. Inspect for bearing or spindle damage and repair.

6. Worn Deck Belt

When a mower deck is worn and stretched leaving some slack, the belt will not sit securely around the pulleys.

This extra slack, as the belt moves around the deck, can cause your deck to vibrate. Replace a worn belt if you find it is stretched, cracked, or has a glazed appearance.

If the belt appears in good condition, make sure it is routed around the pulleys correctly and the tension is adjusted to remove extra slack.

7. Bad Pulley Bearings

A vibration in the mower deck can be felt through your Simplicity mower when you are using bad pulleys. The bearings can fail. This will cause the pulleys to wobble and no longer sit securely parallel to the deck.

Where there is a wobbling movement to the pulleys, the mower deck will shake as your belt runs around the pulleys.

Check each pulley to make sure it is securely attached to the deck and doesn’t have a wobble or signs of bearing failure.

You don’t want a lot of movement in the pulley where one side of the pulley sits higher off the deck than the other. When this happens, you most likely have a bad bearing on the pulley.

Find a failing bearing by slowly rotating each pulley by hand. Feel for a restriction and listen for bearing noise. If you experience either of these, your pulley and bearing assembly will need to be replaced.

8. Worn Idler Bracket & Spring

A loose or worn idler bracket and spring can make your mower shake. The hole in the bracket where the spring attaches can wear larger and the spring can become stretched.

When this happens, you will experience a vibration. Replace a worn idler bracket or spring.

9. Debris Lodged in the Mower

Check your zero turn for small debris stuck in the crevices of the mower. When mowing the lawn, your mower kicks up the debris that can collect on your mower. Something as small as a wood chip can cause extreme vibration in your mower.

Remove your spindle covers and clean off your deck regularly. Debris can collect under your pulleys and cause them not to sit flat and parallel to the deck.

Debris buildup can also affect the tensioner where it is no longer able to keep proper tension on the belt. This will cause extra slack and your mower deck to shake.

Look every part of your mower over carefully and remove any items that are lodged in your mower. It is best to clean your Simplicity after each mowing to keep it free of debris not only to prevent vibration problems but also corrosion from moisture in the debris.

Need help with cleaning procedures? Check out “How to Clean Your Mower for Best Performance“.