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This is Why Your SCAG Lawn Mower is Vibrating and Shaking

You may be lucky enough to have a mower with a suspension system or one of those upgraded suspension seats to help minimize the vibration you feel when mowing the lawn.

Even with steps taken to minimize vibration, there may be times when the shaking is so bad, you feel like you’re going to shake right out of the seat!

A SCAG lawn mower may begin vibrating from loose, worn, or missing engine mounting bolts; a bad clutch; incorrect or unbalanced mower blades; a damaged spindle or spindle bearing; a worn deck belt; a bad pulley or tensioner; or debris lodged in the mower.

Before looking for your vibration problem, refer to your operator’s manual for all safety precautions for your SCAG model. Make sure your mower will not start by disconnecting the spark plug boot. Wait for all moving parts to come to a stop prior to performing any diagnostics or repairs.

SCAG mower is vibrating

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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.

8 Reasons a SCAG Lawn Mower is Vibrating and Shaking

Engine Mounting Bolts

While your engine is running, it vibrates. To help absorb some of that vibration, you will find engine mounting bolts under the engine. These are sometimes referred to as motor mounts.

Over time, these bolts can become loose, wear or break causing you to feel added vibration while operating your SCAG. Inspect these bolts to confirm that are in good shape.

Replace any worn damaged or missing engine mounting bolts to minimize the amount of shaking coming from the engine.


Your SCAG lawn mower will most likely have an electric clutch. This type of clutch has a bearing that can fail to send a vibration through the mower. Replace the clutch when this happens.

Mower Blades

There are many items in your mower deck that can cause a vibration including your SCAG mower blades. Using the wrong blades for your mower or blades that are unbalanced can cause them to wobble, spin unevenly and vibrate the mower.

Wrong size lawn mower blades:

While I choose to use OEM (Original Equipment Manufacturer) blades so I can make sure I’m getting a good quality blade of the right size, you may choose to use an aftermarket blade.

There may be aftermarket blades that work well on your SCAG mower, but you have to be careful when choosing blades.

Not all blades that are of the same blade length and center hole size as the OEM blades will work. There may be slight variations to the blades that will not fit correctly on your mower causing potential spindle damage and vibration.

I find it’s best to physically match up a potential aftermarket blade to an OEM blade to confirm it’s the right fit. Once you find a good OEM or equivalent blade for your SCAG, use the correct hardware when installing the blade.

Unbalanced mower blades:

Mower blades on your SCAG can be unbalanced causing the blade to wobble as it rotates under the mower deck. At high speeds, this can cause severe vibration. It may even cause bearing damage in the spindle housing.

An unbalanced blade is one that weighs more on one side of the blade than on the other side. There are a couple of ways a blade usually becomes unbalanced:

  • Uneven Wearing: Dirty that gets sucked into the underside of the mower deck will wear the blades. When uneven wearing occurs, the blades can become unbalanced.
  • Incorrect Sharpening: During the blade sharpening process, more metal is removed from one side of the blade than the other. Find out more about sharpening and balancing your blades here.

Material Around the Blade Spindle

The mower deck can draw debris and foreign materials to the underside of the deck. Items like string, wire, and even long sturdy weeds can become wrapped around the spindle shaft. This can cause the mower to shake.

Inspect the spindle shaft on your SCAG mower to ensure there isn’t any foreign material wrapped around it. The spindle shaft, also known as the blade shaft, is the round rod-shaped part where you attach the mower blade.

If you do find material wrapped around the shaft, remove it and then proceed with steps from the next section to check for damage to the spindle or spindle bearing.

Spindle Components

A spindle can bend and the bearing can become damaged. This happens when you hit something solid under the mower deck. A bearing can also fail over time. When either item is damaged or worn, it must be replaced.

When the spindle is bent and the bearing isn’t securely in place, it can cause extra movement with each turn of the blade. This will cause a severe vibration coming from the mower deck.

To check your SCAG mower deck spindle and spindle bearing, put on a heavy pair of gloves to protect your hands from the sharp blade edges. Next, grab ahold of the blade and rock it up and down.

While you do this, feel for any extra movement. You may even hear a knocking sound. If you find there is movement and the blade doesn’t securely in place, you most likely have a problem with the spindle or bearing.

Remove the blade and spindle and housing to inspect them for damage. Replace a damaged spindle or bearing.

While some manufacturers only sell complete spindle housing assemblies with bearings included, the bearing can be replaced in the spindle housing on most SCAG lawn mower decks making it less expensive to repair a failed bearing.

Deck Belt and Pulleys

The belt and pulleys on the deck can also cause your mower to begin shaking. A belt that is worn may not sit securely around the pulleys. The extra slack will cause vibration and the belt may actually fall off.

Check your SCAG deck belt for signs of wearing. You’re looking for cracks developing in the belt, a stretched belt, or a glazed shiny appearance to the belt.

If the belt appears to be in good condition, check to make sure it is routed around the pulleys correctly and there is good tension on the belt to keep it in place.

Next, take a look at the pulleys on the deck. These need to be securely attached while sitting parallel to the deck. If you find a pulley that is not sitting parallel, but more like at a slant to the deck, you probably have a bad pulley bearing.

You can also find a bad or failing bearing by slowly rotating each pulley by hand. Feel for a restriction and listen for bearing noise. These are signs of a bad bearing that must be replaced.

You will be able to replace the bearings in some pulleys, but not all of them. Some pulleys, like the idler pulleys, may have a sealed bearing where you will have to replace the pulley and bearing assembly.

While you can attempt to replace them, it can be difficult to do this in some pulleys. You may want to save yourself some time and avoid the headache by replacing it with a new pulley and bearing assembly.

Idler Bracket & Spring

The idler bracket and spring on a SCAG mower deck can wear over time. The hole in the bracket can wear larger and the spring can stretch causing it to begin to vibrate.

Replace a worn idler bracket or spring. Check the bearing and bushing in the engagement linkage and replace them if you find they are worn.

Debris Lodged in the Mower

Check your SCAG mower for small debris stuck in parts and small crevices of the mower. When mowing the lawn, your lawn mower kicks up the debris that can get caught in the mower.

Something as small as a wood chip lodged in your mower can cause extreme vibration.

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

Vibration is created when your mower deck moves around the pulley that doesn’t sit flat on the deck.

Small debris can also collect in other areas of the mower, so make sure you look at the whole mower and not only the deck. You could be surprised at what small item could actually be causing such a big vibration.

Still Experiencing Problems with Your SCAG Lawn Mower?

Own a lawn mower long enough, you’ll start running into problems with it starting, not continuing to run, smoking, leaking gas, giving a bad cut, vibrating, or another issue.

To help you save time and money, I have put together a guide to help you troubleshoot the next problem that develops on your mower.

You can find this guide at Common SCAG Lawn Mower Problems & Solutions.

If you are unsure how to perform diagnostics and repairs on your lawn mower safely, it’s best to have a professional complete the repairs.

This will help you avoid personal injury or additional damage to the mower. Your local SCAG lawn mower dealership or lawn mower repair shop will be able to help you solve your problem.