The best scenarios to have when your zero turn seams weak on one side are a low tire, bad steering dampers, a hung-up brake, air trapped in the hydraulic system, or the load is unbalanced.
You may need to change your hydraulic oil and filter or you may have a more serious and costly issue like a transmission pump and wheel motor failure.
Reasons a Zero Turn is Weak on One Side
1. Low Tire Pressure
Begin identifying your problem by checking the tire pressures. A low tire can cause the mower to pull to one side giving the appearance that one side of the mower is a little weaker than the other.
The tire pressures must be equal on both sides. A low tire pressure will not only affect movement but it will also leave you with an uneven cut.
2. Bad Steering Dampers
The steering dampers are little gas shocks attached to each steering lever to help with smooth control when using the levers.
When a damper fails, you may feel a jerky movement when operating your zero-turn. As you move the steering lever forward, the mower may feel weak and not as responsive on the side with the bad damper.
Locate the damper to make sure it is securely in place. Tighten any hardware if it appears loose. Replace the damper if it is bad.
3. Brake Hung Up / Wheel Not Freely Moving
Depending on the type of brake system your mower uses, you may have a wheel that is not freely moving because a brake component is not working.
The best way to find out if the wheel is meeting resistance is to raise the rear of the mower off the ground using jack stands to securely hold it in place.
Then disengage the transmission using the bypass levers so the wheels move freely. Spin each wheel to check for resistance. Repair or replace the items causing the resistance.
4. Tracking Needs Adjustment
One side may seem weak when your mower keeps pulling to one side. This may be due to one tire moving faster than the other.
In order to fix this, you will need to adjust the speed adjustment bolt to change the rotation speed of the tire so both tires move at the same speed. This can vary a little with each zero-turn so consult your operator’s manual for instructions.
5. Low, Bad, or Old Hydraulic Oil
Using fresh hydraulic oil and performing routine oil and filter changes are required is crucial to keeping your transmission system working at its best.
A low oil level or old oil may not provide sufficient lubrication and cause one side to feel not as strong as the other because of the weak hydraulics.
Make sure the hydraulic oil level is at the FULL COLD level on the overflow tanks. Add fresh oil until it reaches that level. It’s also good to check for leaks if you have a low oil level.
Change your hydraulic oil and oil filter if you are past the service interval recommended by the manufacturer.
Note: Some entry-level zero-turn mowers will have non-serviceable transmissions also known as sealed transmissions. The fluid cannot be changed in these types of transmissions. Contact your local dealership for assistance with these transmissions.
6. Air Trapped in the Hydrostatic Transmission
After changing the hydraulic fluid, you must bleed all of the air out of the system. Air in the system can prevent one side of your mower from working and feel like it’s losing power on one side.
Air can be removed from the system on most zero-turn mowers by placing the mower on a flat surface.
Secure the front wheels using wheel chocks to prevent the mower from rolling forward. Raise the rear drive tires off of the ground and allow them to spin forward and backward until you don’t hear excessive noise and the wheels move at normal speeds.
Refer to your operator’s manual for detailed steps to remove air from your model’s hydraulic system.
7. Bad Pump or Wheel Motor
The hydrostatic transmission on a zero turn is two separate systems that consist of a pump and wheel motor for each side of the mower. This allows each wheel to operate independently from the other.
One wheel is able to move forward while the other wheel is able to move backward allowing it to turn at a zero radius. When you move the control lever forward or backward, the hydraulic flow increases to the motor which increases how fast your move.
When the pump begins to leak or the wheel motor fails, the best thing to do is replace it. This is going to be an expensive part to replace.
Some may recommend purchasing a pump rebuild kit, but in my experience, this may work for a little while but the pump will most likely end up needing to be replaced.
8. Load is Unbalanced
Mounting a grass catcher, pulling a trailer, or attaching another item to your zero-turn can cause it to pull to one side making it appear one side of the mower is weaker than the other.
Make sure the weight of the load is centered on the mower.