Zero Turn Mower Weak On One Side (Why + What to Do)

Zero-turn lawnmowers are very popular because they operate differently than other traditional mowers. Lawnmowers are handy gardening and lawn care equipment that require routine maintenance and repair. For zero-turn lawn mowers, one-sided weakness can indicate tire problems or internal part malfunction.  

In many cases, your zero-turn mower may be weak on one side due to low tire pressure, a faulty deck belt or drum brake, damaged splines, or misalignment. However, these problems can be fixed by routinely replacing necessary parts and ensuring your mower’s wheels or parts operate properly. 

Many home and business owners dread having to repair their mowers or fear their lawnmower is entirely broken. But this isn’t always the case. This article will review the common ways a zero-turn mower may be affected and the right solutions that can resolve the issue. 

Reasons Why Zero Turn Mower Is Weak On One Side 

At times, different types of lawnmower problems may leave homeowners wondering why their zero turns are weak on one side. However, Zero turn mowers are different from traditional mowers because they don’t use common systems such as brake pedals and directional movement. In these cases, it’s important to understand how your mower may be affected by the following common issues. 

Low or uneven tire pressure

A common mishap that causes weakness for one side of a zero-turn mower is low or uneven tire pressure. Since mowers move with wheels in place, the stability and function of your mower may be affected when tires are not adequately filled with air. 

Like a vehicle, a mower will often lean to one side when the affected wheel is not inflated adequately. This could be affecting the strength of your mower on one side if the wheel is flat or significantly lower than others. 

Your mower may drive slowly, get stuck while mowing, or stop working if the tires are uneven. In these cases, checking the tire’s state, size, and air compression can help determine if this is the cause. 

Damaged or broken deck belt 

In a lawn mower, the deck belt is important for turning the blades while mowing. The deck belt is located outside the mower deck and connects the pulleys to turn your mower blades. Commonly, deck belts are among the first pieces of a zero-turn mower to be affected after use. 

Common causes of a damaged or broken deck belt include: 

  • Normal wear and tear
  • Grass clippings getting trapped in the deck
  • Missing belt guard 
  • Wear and tear of the pulley 

The deck belt and pulley system need to move freely. This may be the causing weakness on one side of your zero-turn mower if you notice your deck belt is damaged or the pulley system is frayed. 

Faulty Drum Brake 

A drum brake is located on two wheels of a zero-turn mower. If there is an issue with the drum brake, you may notice one side or both are affected when trying to mow your lawn. The wheel that is affected will often drag or cause difficulty when moving. 

You may be used to hitting a brake pedal to stop moving a car, but the brake process is not the same for mowers. The drum brakes work as a parking brake, and when engaged on either side of the mower, it can cause a lag or dragging motion. 

Additionally, if your mower has disc or drum brakes, one side may not release as well as the other. The uneven function of the brakes can cause brake calipers to stop working. As a result, brake pads can get misaligned and cause problems when trying to move your mower. 

Damaged or Stripped Spline 

Splines are similar to keys, in that they fit into the hub and shaft of mower wheels. This is an important aspect of keeping mower wheels moving freely and without stalling. 

In a zero-turn mower, you can find splines within the pulley system of wheels. When stripped or damaged, splines may be the cause of weakness on one side of your mower. Routinely checking your wheels and ensuring the pulley system is not frayed or damaged can help avoid low mower function. 

Unaligned Tracking 

In a zero-turn mower, two hydrostatic motors are tracked and guided by handlebar movement and alignment. A tracking rod is also connected to the motors, and both sides have to maintain alignment to mirror each other and work properly. 

If you notice any obstructions in your tires, lap bars, steering lever, and mower bolts, this may be contributing to misalignment and affecting tracking. Whether in your wheel tracking or steering lever, maintaining alignment can help avoid uneven sides while mowing. 

Possible Solutions For Zero Turn Mower Weak On One Side 

When seeking to resolve one-sided mower weakness, it may be necessary to replace certain parts or practice routine lawnmower maintenance. However, you should review the safety measures in replacing lawnmower parts and how to avoid health hazards such as carbon monoxide poisoning. 

Here are common ways to fix zero-turn mower weakness on one side: 

Check and adjust tire pressure

If uneven tire pressure is causing weakness on one side of your mower, checking the tire pressure and adjusting it as needed is a quick solution. As long as your tires are not damaged, worn, or broken, adjusting the air pressure should resolve the issue. 

First, you’ll want to inspect the tires and evaluate if there is any unequal tire pressure by using a tire pressure gauge Standard mower wheels will state the maximum PSI for each wheel. If the tire pressure is low or uneven compared to others, adding air pressure may fix it. 

Replace a damaged deck belt 

If your deck belt is damaged or worn, it may be worthwhile to replace it and avoid further issues. The belt should be replaced once every two years with regular use, or less frequently if you don’t use your mower all that often. 

In cases where the belt is damaged, frayed, or seriously worn from excessive use, replacing it can protect the overall use and performance of your mower even if the replacement is sooner than expected. 

With the mower turned off, remove the deck and belt guards. Next, you’ll want to loosen the bolts of the pulleys and make note of the belt’s route to replace it with the new one. After you’ve added the new belt, adjust the pulleys, and replace the rod and guards. 

Rebuild and replace the drum brakes 

Replacing drum brakes can help resolve uneven mowing on a zero-turn mower when the brake system may be to blame. If this is the case, you’ll want to start by disconnecting the spark plugs while your mower is off. 

Next, remove the hub nut from the wheel and jack up the mower for better reach. Once you inspect the brakes if you notice any part of the shoes or springs are not working properly, replace the brakes and remove them. 

Remove the brakes by using pliers to remove the springs and remove the brake shoes. After that, install the new brake shoes and wheel hub. You’ll want to check the wheels by spinning them and if installed correctly, the rubbing should be resolved. 

Replace spindles or check for disengaged splines

Replacing spindles can help repair your mower when it’s weak on one side. If the splines are disengaged, you can adjust them and fix a one-sided mower malfunction. At times, replacing blades can also help the functioning of the mower. 

Typically, routine mower maintenance can require replacement spindles to ensure the mower’s blades work properly. You can also purchase splines at mower repair shops if the splines require replacement to help the blade move and stay in place. 

For this solution, you should find a good brand of reliable parts to ensure the shaft splines fit tightly on the blade. To replace the spindles, find the right size and remove the mower deck belt and spindle assembly cover. Follow the spindle’s spline and adjust with the new spindles. 

Adjust tracking and alignment 

If the tracking or alignment is out of sync in a zero-turn mower, the mower’s function and stability are affected. To adjust the alignment and ensure your mower is aligned, start by centering the drive bars. 

Make sure the bolts are firmly connecting the bar to the pivot arm. If bolts are loosened, adjust and straighten the bar. Then, use a socket wrench tool to tighten the bolts with the bar aligned in place. 

At times, you may need to adjust the forward or backward movement of the bar. In these cases, follow the steps to adjust the rear bolts and test the bar by moving in the desired direction. If this does not work, move on to adjust the tracking by adjusting loose bolts affecting the link rod on the affected side. 


Zero-turn mowers can be affected by different issues such as brake mishaps, misalignments, stripped splines, or other issues. Uneven or uninflated tires are commonly a problem when it comes to zero turn mowers, and air pressure may be the solution in these cases.  

Depending on the cause of your mower’s weak side, routinely checking your tires and replacing necessary parts such as a drum brake, splines, or deck belt can help you avoid uneven performance while mowing. Overall, your mower may need regular maintenance and replacement parts to resolve one-sided problems.

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