Having a weak side on your zero-turn mower will be noticeable quickly. Feeling that one side is dragging or sluggish is common with zero-turn lawn mowers and can be diagnosed relatively simply once you know where to look. I’ve listed some of the common issues that cause this unbalanced feeling and how to diagnose them. So, let’s take a look at why your zero-turn mower pulls to one side and how to fix it.
Why a Zero Turn Mower Pulls to One Side (The Short Answer)
Zero-turn mowers, unlike other designs, use two independent systems to power the drive wheels. Either side of the drive system can fail, including the wheels. Attachments to the mower, such as clipping bags and trailers, can also throw off the balance and make one side drag.
It Feels Like My Zero Turn Mower is Weaker On One Side – Why?
If it feels like your zero-turn mower pulls to one side, then there’s an issue that needs to be fixed. Here’s my list of potential causes and how you can diagnose the problem you may be dealing with.
Tire Pressures Do Not Match
Now, you don’t need to have a flat tire to feel the effects of uneven tire pressure. Enough difference in the tire pressures can cause one side to drag. With independent control of the wheels in your hands, you will be very aware of how either side performs and responds to your movement. As a result, you’ll feel when the tire pressure doesn’t match.
Park your lawn mower on a level surface like your driveway, and grab a tire pressure gauge. Check on the side of the tire for the max PSI, and then compare it with your tire’s PSI. Do this for all the tires to see which one is causing the zero-turn mower to feel weak on one side.
Dragging Drum Brake
You’ll find that your zero-turn mower has two drum brakes, one on each wheel. These brakes are used with the parking brake feature of your mower. Things can go wrong between the drum itself and the engaging mechanism, causing the brake to drag or rub, giving the feeling that one side is struggling. The quickest way to tell if there’s a problem with the drum brake is to choke the front wheels, disengage the hydros, release the brake, and jack up the rear of the mower so that the wheels are off of the floor. Next, spin the wheels and check for any difference in resistance. The wheel that you felt was dragging should be harder to turn.
Air Lock in the Hydrostatic Motor
When you’re out using your mower, you may experience cavitation of the hydraulic fluid used in the hydrostatic system. This is where air forms in the fluid. Once this air accumulates, it can cause an air pocket in the hydro system. Now, this can occur in just one of the hydro motors of your mower and cause the lack of power to just one side.
To diagnose this, drive your mower on a flat surface at a low speed, and see how it feels as you increase it to a high speed. The effect becomes worse with increased power depending on how bad the air pocket or airlock is. So, if you feel it gets worse as you transition from a low to high speed, you can be pretty certain you have an airlock. Once the airlock gets too bad, the wheels won’t turn at all.
Tracking Out of Sync
The two motors are tracked through handlebar movement, alignment, limits, and the tracking rod connected to the hydrostatic motors. This basically means that both the left and right sides of the controls should mirror each other.
To check this, see how the handlebars line up and move together. So, with the engine off, pull the bars together and check if they line up, then push the bar forward fully and see how they line up. If you find that they are out of line, they’ll need to be adjusted.
You’ll also want to check under the mower if they line up. Connected between the handlebar and the hydro motor is a link rod. As you move the handlebars, the connection rod moves the plate into the hydro motor. Both plates should be positioned evenly. If the handlebars, rod, or plate are out of line, one side will feel weak while the other feels strong.
My final check is to drive the mower in a straight line regardless of the position of the handlebars. Once you’re moving along, glance at the handlebars and check how they line up, I’m guessing they’ll be totally out of line and need some serious adjustments.
Out of Balance
The problem with your zero-turn having a weak left side or right side could be down to the load it is carrying or dragging. I’ve seen all sorts of things being towed behind zero-turns, like garden rakes, blowers, and trailers. You name it, I’ve seen it.
Anything unbalanced on or behind your mower could cause one side to drag. The most straightforward test is disconnecting or dismounting any load attached to the mower and giving it a run down the lawn.
How to Fix a Zero Turn Mower that is Weaker on One Side
Now that you have figured out the potential causes for your zero-turn mower being weak on one side, let’s get down to fixing the problem. Here are my best solutions to evening up the power and getting the mower driving straight again.
Matching Up the Tire Pressure
Fixing the tire pressure is probably the easiest of fixes, but it’s probably the one that gets skipped the most. All you need to do is test the four tire pressures and inflate them to the recommended PSI. This is going to save a lot of uncomfortable driving and improve the cut of the lawn.
- Tire Pressure Gauge
- Tire Pump
Fixing the Drum Brakes
Start by getting your mower on a level surface and disconnecting the spark plug. Then, chock the front wheels so the mower can’t move and release the parking brake.
Loosen the Hub Nut
First, you’ll want to loosen the center nut of the wheel. This is the bolt that holds the wheel hub to the lawn mower. A socket wrench with a long extension should work fine. If you find that you have a cotter pin through the nut, then you’ll need to remove this first using a pair of pliers.
Jack Up the Mower
Next, jack up your zero-turn mower’s rear so that the rear wheels are an inch or two off the ground. Now you can use your wheel wrench and remove the nuts/bolts holding the wheel on.
Remove the Hub
Screw off the hub nut and remove the wheel’s hub. This could take some extra effort since there is a problem with the brake rubbing.
Inspect the Brake
Take a look and inspect the brake shoes. You should find two shoes, two springs, and an adjustment screw. If the shoes were dragging, then there’s going to be a problem with one part of the system.
But, on the other hand, if one of the parts failed or the brake was too tightly adjusted, then, unfortunately, the shoes are likely worn and unsalvagable.
Remove the Brakes
Remove the springs linking the shoes together using your pliers and set them to one side. With the spring removed, you should be able to lift the shoes out of position. Once again, put them to one side along with the attached adjustment screw.
Install the New Brake Shoes
Next, take your new brake shoes and position them on the lawn mower. You will probably find that each shoe is specific to one side. Then, reinstall the adjustment screw between the shoes, turning the adjustment screw so that the shoes fit closer to each other.
Install the Wheel Hub
Next, you can go ahead and install the wheel hub and nut. Tighten the nut the best you can so that the hub is firm.
Test for Rubbing
Give the wheel a spin and check for any resistance. If the brake was installed correctly, there should be no resistance, and the hub should spin freely.
Reassemble the Mower
Next, grab your wheel, place it back on the mower, and screw on the nuts/bolts. Tighten all the nuts/bolts using your wrench, then lower the mower. Finally, double-check everything is tight and install the cotter pin.
Adjusting the Brake
The last thing you’ll need to do is adjust the brake. On the back side of the hub, you’ll find a hole where you can adjust the shoe adjuster screw. Apply the brake and tighten the adjustment screw. This is going to take several adjustments until you get it right. Just remember not to over-tighten or you’ll be dealing with a dragging brake again.
- Wheel Chocks
- Wheel Wrench
- Socket Wrench with Extension
- Brake Shoe Kit
Air Lock in the Hydrostatic Motor
For this fix, you’ll need to lift the mower once again. Start by chocking the front wheels so the mower can’t move and jack up the back wheels off the ground a few inches.
Release the Hydro
You’ll find the hydro engagement rod on the rear of your zero-turn. Pull/push the rods on both drives to disengage the drives.
Start the Engine
Next, take a seat on your mower and start the engine and increase the throttle to max RPM.
Engage Forward Drive
Apply forward drive to the mower, reach maximum forward drive, and hold for several seconds. If the hydros were correctly disengaged, the wheels will not turn when you apply forward or reverse drive. If they do, switch off the mower and correctly disengage the hydros.
Engage Reverse Drive
After engaging forward drive, you’ll want to switch to reverse and hold for several seconds. Repeat the forward and reverse motion a few times. This will bleed the hydrostatic drive and remove the air from the motors. When finished, switch off the engine.
Lower the Mower & Re-Engage
Lower the jack to get the mower back on the ground and apply the brake. Next, engage the hydros using the engagement rods and remove the chocks.
Check Hydro Fluid Level
Check your hydro fluid levels if you are able to do so. If you notice your level is low, top off with hydro fluid. Some hydros are sealed and don’t allow you to add fluid. If that’s the case with your mower, then you’ll need to skip this part.
Test the Mower
Finally, take the mower for a test run. Bleeding the hydros can take a couple of attempts, so you may need to repeat the process to get out the last little bit of air. I suggest taking your time and not rushing since you’ll just have to jack up the mower again.
- Wheel Chocks
- Hydro Fluid
Tracking and Alignment Out of Sync
Tracking needs to be carried out in two stages; bar alignment and drive tracking. I like to start by aligning my bars first since this means tracking to bars that I know are straight.
Center the Drive Bars
First, pull the bar into the center and check if they line up. If one is further forwards than the other, then you need to adjust the bolts connecting the bar to the pivot arm. By following down the handlebar, you’ll come to the bolts that attach the bar to the pivot. Loosen the bolts on one side using your socket wrench and align the bars. Once the bar is aligned, tighten up the bolts.
Adjusting the Forward Movement.
Next, push the bars all the way forward and check to see if they are still aligned. At the bottom of the bar, where it passes into the mower, you’ll notice that an adjustable bolt stops the bar. Adjusting this bolt on either side will limit the movement of the bar in the forward direction. If your bars don’t line up, adjust the bolt to either increase or decrease the distance the bar can travel.
Adjusting the Reverse Movement
In the same way you adjusted the forward movement, you’ll need to adjust the backward movement. Push the bars into the full reverse position and check for alignment. Then, make the adjustments you need by adjusting the rear bolt.
Test the Mower
Once the bars align in forward, center, and reverse, you can test the mower. You’ll most likely find that these adjustments have fixed the issue. However, if you still find that your zero-turn mower is weak on one side and the mower won’t drive straight, then you’ll need to move on to tracking.
Locating the Tracking Adjustment
Tracking is the process of aligning the drives so that equal movement provided to the bar is transferred to the drives. Under the mower, you’ll find the link rod connecting the bar to the drive. As it connects to the drive, you’ll notice that the adjuster plate is sandwiched between two bolts. Moving these bolts either up or down the rod will increase or decrease the drive speed. What you need to do is match the speed between each drive wheel.
Picking a Side
It doesn’t matter if the zero-turns left side is weak versus the right side. You need to either increase the slow side or decrease the fast side. If you have an extreme case of bad tracking, you’ll want to increase the slow side halfway and decrease the fast side halfway. This will eliminate the risk of increasing and decreasing the mower’s overall max speed. I usually increase the slow side if it’s just a little off.
Adjust the Link Rod
Once you have picked which side to tackle, you’ll need to adjust the two nuts either up or down the link rod. Mowers work differently, so if you don’t know which way to adjust the nuts, then just give one way a try. Loosen off the rear bolt with a few turns, then adjust the front bolt to re-sandwich the adjuster plate nice and tight. Once done, give the mower a test run. You’ll quickly see how your adjustment worked. You’ll not likely get it right the first time, so repeat the process until you get the mower running straight with equal power on both sides, with equal input from the bars.
- Socket Wrench
- Wrench Set
Out of Balance
Balancing the mower is a quick fix. Remove all of your attachments and test out the mower. If you find that the problem is solved, you know the attachment was the issue. It may be a case that you are overloading the mower and putting it under too much strain. Alternatively, the extra weight is exaggerating an underlying problem.
My concern is if there is a problem with attachments specifically designed for your mower by the same manufacturer, such as a grass collection system. I’ve found that grass can collect on one side of the collection bags and unbalance the mower. This can feel like one side of the mower is weak.
A trick is to monitor the collection bag as it fills up. At the point in which you feel the mower change, inspect what’s happening with the collection bags. You could find a problem with clipping distribution. This could mean it’s time for a repair or a call to the supplier.