A Kubota lawn mower is pretty comfortable to sit on, especially if you own one of their suspension seats. That comfy ride can quickly turn into a bumpy uncomfortable ride when a vibration develops in the lawn mower.
A Kubota lawn mower begins vibrating when the engine mounting bolts are loose, worn, or missing; the clutch is bad; the mower blades are incorrect or unbalanced; the spindle and spindle bearing is damaged; the deck belt is worn; the pulleys or tensioner are bad, or debris is stuck in the mower.
Before looking for your vibration problem, refer to your operator’s manual for all safety precautions for your Kubota model. Make sure your mower will not start or move while performing any work.
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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.
Reasons a Kubota Lawn Mower is Vibrating
Engine Mounting Bolts
A running engine causes the Kubota mower to vibrate, but most of this vibration is absorbed by the engine mounting bolts. These are bolts installed under the engine that can become loose, wear or break over time. Inspect these bolts and make sure they are in good shape.
Replace any that are worn, damaged, or missing to minimize the amount of vibration you feel coming from the engine.
Your Kubota lawn mower will use either a manual engagement or an electric clutch. The manual clutch uses belts and pulleys. In this type of system, you need to check the bushings and linkages for failure. Replace any worn parts.
If your Kubota mower uses an electric clutch, the bearing can fail to cause vibration through the mower. When this happens, replace the clutch assembly.
Oftentimes, the cause of vibration is due to the mower deck components. This includes the mower blades. Using incorrect or unbalanced mower blades can cause the blades to wobble and spin unevenly.
Wrong size Kubota mower blades:
I prefer to use OEM (Original Equipment Manufacturer) blades to ensure I am getting a good quality blade of the right size so I don’t have to worry about causing additional damage to the spindles when running incorrect blades.
There are often sufficient aftermarket blades available to fit your mower. Just understand all aftermarket blades are not the same. I’m not saying you should stay away from aftermarket blades.
There are some aftermarket blades on the market that are good quality and generally cost less.
Just make sure they have the correct center hole size and blade length. Even with those measurements, the blades can be different than the OEM size so lay an aftermarket blade on top of an OEM blade to ensure you have a good match.
Unbalanced Kubota mower blades:
An unbalanced blade is one that weighs more on one end of the blade than the other allowing your blade to wobble as it spins. At high speeds, this can cause severe vibration in the mower and may even cause bearing damage to the spindle housing.
A blade can become unbalanced from uneven wearing during normal use. Dirt that is sucked under the deck can wear the metal blade unevenly. Another way a blade can become unbalanced is during the blade sharpening process.
To sharpen a Kubota mower blade, a thin layer of metal is removed from the blade edge. When more metal is removed from one end of the blade than the other, the blade is unbalanced. Find out more about sharpening and balancing your blades here.
Material Wrapped Around the Blade Spindle
Even though you checked your lawn to remove rocks, sticks, toys, and other items left in the yard, you may still miss things that can get caught in the deck causing a vibration.
Narrow thin items like string, wire and even long sturdy weeds can wrap around the spindle shaft.
Inspect the spindle shaft to ensure there aren’t any foreign materials 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.
A spindle can become bent and a bearing can become damaged when the blade impacts a hard stationary object. A bearing can also fail over time. When either of these items is damaged, they must be replaced.
The extra movement created from these damaged parts can create a bad vibration in the Kubota mower deck.
Before you check the spindle housing, put on a good pair of work gloves to protect your hands from the sharp edges of the mower blade. Next, grab a hold of each end of the blade and rock it up and down.
What you’re doing is feeling for any movement. You may also 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 replace the damaged items.
If you find bearing failure, the bearing can be replaced in the spindle housing on most Kubota lawn mower decks. However, there are some models where you must replace the complete spindle housing assembly.
Deck Belt and Pulleys
The pulleys and mower deck belt may cause your shaking problem. When the belt is worn or has slack, it will not sit securely around the pulleys and may be loose or come off. 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 your belt is routed around the pulleys correctly and the tension is adjusted to remove extra slack. Your belt may also not be sitting securely around the pulleys because the pulleys are not sitting parallel to the deck.
Check each pulley to make sure it is securely attached to the deck and doesn’t have a wobble to it.
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 bearing must be replaced.
Note: Some pulleys will only use sealed bearings. In this case, you will have to replace the pulley and bearing assembly.
Idler Bracket & Spring
The idler bracket and spring can wear over time. The hole in the bracket can wear larger and the spring can stretch. A loose idler bracket and spring can make your Kubota 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.
Check your Kubota mower for small debris stuck in parts and small crevices of the tractor. When mowing the lawn, your lawn mower kicks up the debris that can collect on your tractor.
Something as small as a wood chip can cause extreme vibration. 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. Vibration is created when your mower deck moves around the pulley that doesn’t sit flat on the deck.
Still Experiencing Problems with Your Kubota 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 Kubota mower.
You can find this guide at Common Kubota Lawn Mower Problems & Solutions.
If you are unsure how to perform diagnostics and repairs on your Kubota 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 Kubota lawn mower dealership or lawn mower repair shop will be able to help you solve your problem.