13 Reasons Your John Deere Mower Cuts Uneven

You want to achieve the best cut from your John Deere lawn mower, but lately your yard doesn’t look as good as it once did after you mow it. It is now a little uneven. I’ll help you determine where to start troubleshooting your cutting problem and how to solve it.

A John Deere lawn mower may give you an uneven cut when the tire pressures are not correct, the mower blades are worn or damaged, the spindle bearings are damaged, the deck is not level, the mower deck is clogged or the ground speed is too fast.

With so many things that can throw off your good cut, I have put together a complete list of causes and solutions to your bad cut. Follow all safety precautions found in your owner’s manual before performing any work on your John Deere

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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.

Why Your John Deere Mower Has an Uneven Cut

John Deere Mower Blade is Worn or Dull

A John Deere blade that is very worn can leave behind strips of uncut grass between the blades. This occurs when the dirt is sucked into your mower deck and wears down the metal of your blade.

There is no way to prevent the wearing of your blade. It’s just a common wear item on your mower.

You must check your mower blades frequently and sharpen them when they are dull or replace them when they become worn. This includes when the sail of the blade becomes thinner than the center of the blade.

You can find more about what to look for when inspecting your John Deere mower blades here. This will help you better determine when a blade can be sharpened and reused or when a new mower blade needs to be installed.

John Deere Tire Pressures are Not Correct

When you notice your John Deere is cutting the lawn unevenly, you may immediately start looking at your mower deck to resolve the problem. While there are many items on the deck that can cause this problem, you must first check your tire pressures.

Uneven tire pressures can cause your mower deck to not sit level. When your tire is low on one side of your mower, the deck will also sit lower on that side.

It’s important to make sure the pressures on each side of your mower are equal and brought to the pressure level as shown on your tire sidewall.

Not taking time to check your tire pressures prior to addressing problems on your deck can result in making changes to your deck that may not be an issue. Do not skip checking your tire pressures before moving on to checking for bent blades and an unlevel mower deck.

John Deere Mower Blade is Bent

A bent mower blade, whether it’s slightly bent or severely bent, can cause your John Deere to give you a bad and uneven cut. You can bend a blade when it contacts a solid object.

This could be a tree root, rock, dog toy, or some other object left in your yard. It’s a good idea to walk your yard prior to mowing it to make sure you don’t run over any surprises that can damage your blade.

The impact you receive when bending a blade can be so significant you can feel a jolt or hear the blade grind on an object. Other times, you may have not even noticed the impact and don’t know to check for blade damage.

Before you check your blades, take safety precautions to avoid injury. Park your mower on a flat surface and set your parking brake.

Remove your ignition key and disconnect the spark plug wires. Always wear a good set of work gloves whenever you work near or with your mower blades.

There are two methods you can use to check for a bent blade on your John Deere lawn mower:

Check for Bent John Deere Bladeby Removing the Blade:
Gain access to the bottom of your John Deere mower deck. Remove your mower deck if needed. Remove the blade and lay it on top of a new John Deere blade.

This is a good way to verify your blade is bent. If you find there are gaps between the old blade and the new blade, you must replace it with a new blade.  

Check for Bent John Deere BladeWithout Removing the Blade:
With your mower parked on a flat surface, measure one side of the blade from the ground to the blade tip and record the measurement.

Next, rotate the blade 180 degrees and measure the other side of the blade from the ground to the blade tip and record the measurement. If the two measurements are greater than a 1/8” difference, you must to replace your mower blade.

Before you remove your blades, and while under your deck, it’s good to check for spindle housing damage which can happen when a blade encounters a significant impact. Refer to the section below for steps to check for spindle housing damage.

Do not attempt to straighten a bent mower blade and reuse it. Doing so compromises the metal. The metal may crack and fly out of your mower at high speeds. This can put people or pets at risk of injury. It can also cause damage to structures.

John Deere Mower Blades are Installed Incorrectly

I’ve had customers call telling me their new mower is cutting terribly. On many occasions, I have found the first time they installed their blades they installed them incorrectly.

The blades were put on upside down. Of course, placing blades upside down will cause an uneven cut.

Install with the sail pointing upward
When blades are installed incorrectly with the sail facing downward, the blade is tearing and bruises your grass instead of giving it a nice precise cut. The sail can also hit the ground causing impact and damage to your spindle housings.

The high side of your John Deere mower blade, as known as the sail or fin, should be pointed upward toward your mower deck.

Some mower blades are stamped with the word “BOTTOM” or “THIS SIDE DOWN” on the blade to indicate which side of the blade faces the ground. If you don’t find markings on your blade, just remember “Sail Up” and you’ll install them correctly every time.

Use the correct hardware & install it in the correct order

Your mower blade may be secured by a bolt and washer; a nut and washer; or other combination of hardware. Refer to your owner’s manual or John Deere parts diagram to make sure you are using the right hardware and are placing them in the right order.

If your lawn mower requires the use of a concave washer, make sure the cupped side is facing your mower blade.

John Deere blades are balanced

Your mower blades must be balanced before they are installed on your John Deere. You don’t have to worry about balancing your blades when you are installing new mower blades.

You do have to ensure blades you have sharpened and are reusing have been balanced for a good cut.

A balanced blade is a blade where the weight is equal on both sides of the blade. If one side is heavier than the other, a metal must be shaved off the heavy side until both sides are of equal weight. The best way to verify you have a balanced blade is with a blade balancer.

A balancer is an inexpensive tool you should use to make sure you don’t cause additional damage to your John Deere deck and engine from the vibration of an unbalanced blade.

Another method to check a balanced blade is by hanging the blade on a nail that is mounted to your wall with the nail head sticking out of the wall about 3/4″ to 1″. You will need to remove metal from the end of the blade that is hanging lower until the blade sits level.

John Deere Mower Deck is Plugged with Grass

A mower deck that is clogged with grass and dirt can cause a bad and uneven cut. Your John Deere mower deck is designed to use the airflow created by your mower blades and the area under your deck to create a suction.

This suction makes your grass stand tall while your mower blade passes by and cuts the blades of grass.

When your deck is full of grass and other debris, the area available to create good airflow is reduced causing a bad cut with your mower. In addition to a bad cut, a plugged mower deck will cause your engine to work harder and possibly shut down.

Scrape your mower deck periodically. There isn’t any way to keep grass and dirt from collecting under your deck, but there are ways to minimize the amount that does collect.

• Don’t cut wet grass: Wet or damp grass is more prone to clumping and collecting under the deck than dry grass. Your tire tracks will show more prominently in wet grass
• Use a silicone or Teflon spray: Coat the underside of your mower deck to minimize the amount of grass that sticks. While this won’t keep all grass from sticking, it may reduce the amount of grass that sticks so you can scrape your deck less frequently.

John Deere Mower Deck is Not Level

A John Deere with an unleveled deck will give you an uneven cut. The deck leveling procedures vary among the different John Deere models.

Refer to your owner’s manual for instructions and specifications to adjust your mower deck. Follow your owner’s manual to level the deck from side-to-side and front-to back.

John Deere Spindle is Bent or Spindle Bearing is Bad

A bent spindle or bad bearing in the spindle housing can cause your mower blades not to give you a good cut because your blade may sit unlevel.

Identify if you have a problem in your spindle housing by first putting on a good pair of gloves to protect your hands from the sharp edges of your blades.

Grab a hold of each end of your mower blade and rock it up and down. Listen for a knocking noise and any movement felt in the blade. These symptoms indicate you need to take apart your spindle housing to find the problem as you most likely have a bad bearing.

Replace the bearing if possible. Sometimes it is not possible to purchase only the bearing and you must replace the whole spindle housing assembly. The option you have varies with the model mower deck you are running on your John Deere.

Bad Mower Deck Belt or Pulleys on Your John Deere

When your mower belt fails to move around the pulleys at high speeds, your John Deere can give you a bad cut. First, check your mower deck belt for signs or wearing including cracks or a shiny appearance.

A belt that sits deep into the pulleys or a belt that is stretched is also a sign of wearing. Replace the belt when you find any of these conditions.

Second, check the pulleys by slowly rotating each pulley. A bad pulley is one where you feel resistance or hear a bearing noise when turning the pulley.

A bad pulley may not sit flat and parallel to the deck. Replace any bad pulleys with a new pulley and bearing assembly.

John Deere Engine Speed is Too Low

Your blade tip speed affects the quality you receive when cutting your lawn.  Your John Deere needs to be running at its top speed to give your deck enough power to rotate your blades at high speeds.

Make sure your mower is running at full throttle when the deck is engaged.

You know your mower best. If you notice the power of your mower is not what it once was, have a small engine mechanic at your local John Deere dealership or small engine repair shop check it over.

John Deere Ground Speed is Too Fast

Know your mowing conditions and adjust your ground speed to achieve the best cut with your John Deere. Your engine will experience heavier loads when it is cutting through thick, tall, or wet grass.

You must adjust to these conditions and slow down so you don’t end up with a bad cut. Moving too fast through your grass can cause you to push over some of your grass and not give it a good cut.

Incorrect Overlapping Path with Your John Deere

I have run short on time and tried to rush my mowing by spacing out my paths so I can cover more ground with fewer passes. When I was finished, I looked at the lawn and noticed strips of grass in the areas I missed.

John Deere Mower Deck Shell is Damaged

The mower deck shell can become damaged when you accidentally hit an obstruction such as a fence post, tree, or building. A tweaked or damaged mower deck shell can be the cause of your bad cut and should be repaired or replaced.

If you are unable to repair your shell, check with your local John Deere dealership to get a price on a replacement shell and a complete deck assembly replacement.

Make sure you also get the cost of labor to swap the components of your deck to a new deck shell for an accurate cost comparison.

Your Lawn is Uneven

Running a wide format deck like a 52” or 60” deck can scalp sections of your lawn when the ground is uneven. It is not able to bend with the dips in the yard so you end up with an uneven cut.

Using a push mower with a smaller deck will give you a better cut when mowing wavy areas of the lawn or ditches.

The mower can also scalp your yard when you have high spots in your yard. To level out, these high spots use a weighted lawn roller to smooth out your lawn.