13 John Deere Hydrostatic Transmission Problems

John Deere Hydrostatic Transmission Problems

A hydrostatic transmission transfers energy using hydraulic fluid. It uses two hydraulic devices. The two are variable displacement pump connected to a motor through hydraulic lines.

John Deere hydrostatic transmission machinery boasts a high power acceleration rate and dynamic abilities.

John Deere has implemented the transmission system in both tractors and zero-turn mowers.

In hydrostatic transmission, the machine does not need gearing to transfer rotating mechanical energy from one power part to another. 

Manufacturers use hydrostatic transmission systems as alternatives to gearboxes for a fixed rearrangement of engine and pump components.

The hydraulic transmission acts as the gearbox by rotating the motor through passing fluids in small flexible metal hoses.

Here are the John Deere hydrostatic transmission problems;

13 John Deere Hydrostatic Transmission Problems and How To Fix Them

Are there problems in John Deere hydrostatic transmission systems? Certainly yes.

They are most often caused by malfunction of the components of the transmission system, a malfunctioning oil reservoir, a hydraulic pump, or a poor hydraulic line.

This comprehensive review covers the causes of the problems and the exact solutions to the problems.

1. Cavitation in John Deere hydrostatic transmission system

This is one of the many John Deere hydrostatic transmission problems caused by air in the hydraulic pumps.

When there is less transmission fluid and more air in the pump, the hydraulic transmission system does not produce enough power to turn the output shaft.

That’s because the air in the pump imbalances the liquid pressure. The liquid pressure is what creates the power to run the output shaft and, ultimately, the wheels of the machine.

Therefore, with the air in there, expect hydrostatic transmission problems.

John Deere hydrostatic transmission repair

We have designed a multiple-step solution to this problem and you can always refer to your John Deere operator’s manual if unsure…

  1. Park the mower on a level surface, switch off the engine, engage the park brake pedal and lift it using the jack stands.
  2. Depending on your John Deere model, fill the oil reservoir with the right oil capacity.
  3. You need to turn off the transmission by pulling out the lever out.
  4. With the transmission disconnected, turn on the engine.
  5. Disengage the clutch and brake pedal and keep the motion control levers neutral.
  6. Move the throttle control to the slow position.
  7. Purge the forward transmission system by pushing the motion control levers and pausing at the end of the push for a while.
  8. Purge the reverse transmission system by pulling the motion control levers and stopping at the end of the pull for a while.
  9. Repeat the push and pull three times as you pause at the end of each push and pull.
  10. Return the motion control levers to neutral, turn off the engine and engage the parking brake.
  11. Check the oil reservoir and ensure it’s holding the correct oil capacity.
  12. Engage the transmission, remove the jack stands, start the engine and disengage the brake pedal.
  13. Move the motion control levers forward for a distance of 6 feet, brake, and return to the original spot.
  14. Engage the motion levers to neutral and if you repeat the movement three times, you will be fine.

2. Hydraulic pumps failure

This is a common problem users face with a John Deere lawn mower. The hydraulic pumps are the core of these systems and their failure could emerge from different areas of the transmission system.

One cause of this problem is air getting into the hydraulic fluids chamber. Since the transmission system depends on fluid pressure to generate power, the air makes it impossible.

Using worn-out pumps and pump belts over long periods also causes this problem. The worn-out pumps will not generate enough power to run the machine optimally.

Running the lawn mower on worn-out parts will cause problems. Running on overused hydraulic oil will also cause this problem.

This is because the axle fluids and hydraulic oil deteriorate in quality with use and start causing problems to the system.

You change your hydraulic fluids after 50 hours of work, depending on your lawn mower model.

Overused front axle fluids may cause steering issues and cause problems for the lawn mower.


The solution to this problem is to replace the broken hydraulic pump. Also, make sure you have the right oil levels in your machine.

Check the hydraulic fluids’ viscosity and ensure it follows the operator’s manual. Use your operator’s manual to check how frequently you should change the fluids.

3. Low levels in the oil reservoir

The John Deere hydrostatic transmission system depends on oil to transfer power to the wheels.

Therefore, when you have low levels of hydraulic oil, power transmission problems arise. The problems range from overheating to general hydrostatic transmission problems.

When you have less oil in the oil reservoir, the hydrostatic transmission will not produce enough power to run the mower’s wheels.


The solution here is to have the correct level of oil in the reservoir. If the oil is at the correct level, your lawn equipment will produce power optimally.

4. Hydrostatic transmission slipping

The design of the hydraulic transmission system should not allow slippage.

Therefore, if you face this problem while operating your lawn mower, you must have common problems with the mechanical parts of your lawn mower.

A slipping belt or a faulty tensioner may cause this slippage problem. Also, broken solenoids or worn-out gear solenoids cause slippage problems.


You should check out the drive belt and replace it if worn or broken. Also, ensure the tensioner is in the best state.

In case the tensioner is faulty, replace it. If the lawn mower runs on broken solenoids, ensure you have replaced them.

5. Old hydraulic oil and steering fluids

When you use the same hydraulic oil and steering fluids over a long period without changing, the transmission system will not create enough power to run the lawn mower wheels.

Sometimes the oil thickens and the thick oil does not reach the pump. When this happens, the hydraulic system becomes too cold to run and may require preheating before running the engine.

With time, old hydraulic oil also deteriorates in quality.


Poor-quality oil will not produce the pressure needed to run the machine’s wheels. Therefore, you need to change the oil.

6. Hydraulic system overheating

If the system is left to absorb too much cold, especially after a long winter, the hydraulic fluids become too thick.

When the fluids are too thick, it becomes challenging for it to get to the pump, causing the transmission system to overheat.


To prevent this issue, always check the temperature indicator on your dashboard and ensure it is not too cold.

If it is too cold, add some anticoagulant to prevent the fluids from thickening. If the system overheats even after adding the anticoagulant, you should seek help from your mechanic.

7. Transmission fluid leakage

The design of the John Deere transmissions is tight, closed and they’re almost leakage-proof systems.

If there is a slight leakage in the transmission system, overheating is inevitable. Any time a leak occurs, the sensors detect a low pressure.

After the sensors detect the pressure issue, your machine may flash out errors such as P0842.

Errors within the region of P0842 suggest that there is insufficient fluid or a leakage in the transmission, which alters the transmission fluid pressure.


Check out all the gaskets and seals in your system. If any of them is broken, replace them. You should also try to find any other parts that might leak the fluids and fix them.

See: John Deere l120 hydrostatic transmission problems

8. Cold hydraulic system malfunction failure

A cold John Deere lawn tractor transmission seriously threatens your system. First, the hydraulic fluid becomes thick and unable to reach the pump.

In the long run, the hydraulic system will not dissipate heat, overheat and damage the transmission.


You need to fill some anticoagulant in your transmission fluid to prevent it from becoming too thick.

Also, if the temperature sensor detects a low temperature too frequently, then you must visit your mechanic.

9. Faulty pump belt

The hydrostatic transmission depends on the drive belt for it to work. If the connection to the pump belt is loose or broken, the motor will not work.

You’ll experience this if your pump belt is old, broken or exposed to excess heat. The pump belt also generates a lot of friction during use and tears and wears out.


Check out the pump belt and replace it if it’s torn or worn out.

10. Hosepipe Issues

Of all John Deere hydrostatic transmission problems, this seems to be critical since the entire system depends on fluids passing through the small hose pipes to drive the motor.

The common problems with the pipe could be fluid leakage, and damaged hoses, mostly from swellings.


You should ensure that the hose pipes in the transmission system are flexible, leakage proof and free from any damage.

You should replace any damaged pipe. If you do not know how to replace it, Google the instructions.

11. Broken and rusted spring

The John Deere Hydrostatic transmission system has many small parts that jointly together allow it to function.

These parts do not work independently from each other and therefore, they generate a lot of friction when used over long periods. 

Springs are the most susceptible to breakdown. This is because they frequently come into contact with water, and rust eventually breaks.

Some of the other parts wear out. If any part of the transmission system breaks, the entire system fails.


The solution to this is identifying the broken part and replacing it. It could be a nut, spring, or a bolt. 

12. John Deere hydrostatic transmission will not engage

If your John Deere hydrostatic transmission isn’t engaging, there are a few possible causes and solutions:

  1. Low Fluid Level: Check the fluid level in the transmission reservoir and add fluid as needed.
  2. Contaminated Fluid: If the fluid appears dirty or has debris, drain and replace it with fresh fluid.
  3. Worn Drive Belt: Inspect the belt for wear or damage and replace if necessary.
  4. Faulty Control Linkage: Check the linkage for misalignment, damage, or disconnection, and make any needed adjustments or repairs.
  5. Mechanical Failure: Internal mechanical issues may require professional diagnosis and repair.
  6. Electrical Issues: Inspect electrical connections, fuses, and switches for faults or malfunctions.

Hydrostatic transmission troubleshooting

Cavitation in John Deere hydrostatic transmission systemAir in the hydraulic pumps causing imbalanced pressure– Park the mower on a level surface, engage the park brake, and lift using jack stands.
– Fill the oil reservoir with the correct capacity. – Turn off the transmission.
– Start the engine with clutch and brake pedals disengaged.
– Purge the forward and reverse transmission systems.
– Return the motion control levers to neutral, turn off the engine, and engage the parking brake. – Check the oil reservoir level. – Engage the transmission, remove the jack stands, start the engine, and disengage the brake pedal. – Move the motion control levers forward and return to the original spot. – Repeat the movement three times.
Hydraulic pumps failureAir in the hydraulic fluids, worn-out pumps or pump belts, overused hydraulic oil– Replace the broken hydraulic pump. – Ensure correct oil levels. – Change hydraulic fluids according to the operator’s manual.
Low levels in the oil reservoirInsufficient hydraulic oilMaintain the correct oil level in the reservoir.
Hydrostatic transmission slippingSlipping belt, faulty tensioner, broken or worn-out solenoids– Check and replace the drive belt if necessary. – Ensure the tensioner is in good condition. – Replace broken solenoids.
Old hydraulic oil and steering fluidsUse of the same oil over a long period without changing, oil thickening or deteriorationChange the hydraulic oil and steering fluids regularly according to the operator’s manual.
Hydraulic system overheatingCold fluids becoming too thickIdentify and replace broken parts like nuts, springs, or bolts.
Transmission fluid leakageLeaking gaskets, seals, or damaged partsInspect and replace any broken gaskets, seals, or parts.
Cold hydraulic system malfunction failureThickening of hydraulic fluid due to cold temperaturesAdd anticoagulant to the transmission fluid. Consult a mechanic if low temperature issues persist.
Faulty pump beltLoose or broken connection to the pump beltCheck the pump belt and replace if necessary.
Hosepipe issuesFluid leakage, damaged or swollen hosesEnsure hose pipes are flexible, leak-proof, and undamaged. Replace any damaged hose pipes.
Broken and rusted springFriction and rust causing breakdownIdentify and replace broken parts, such as nuts, springs, or bolts.
John Deere hydrostatic transmission will not engageLow fluid level, contaminated fluid, worn drive belt, faulty control linkage, mechanical failure, electrical issues– Check fluid level and add as needed. – Drain and replace contaminated fluid.
– Inspect and replace worn drive belt.
– Check control linkage for misalignment or damage and make necessary adjustments or repairs. – Seek professional diagnosis and repair for mechanical failures. – Inspect electrical connections, fuses, and switches for faults or malfunctions.

How to tell if the hydrostatic transmission is bad

To determine if your hydrostatic transmission is bad, look for signs such as power loss, difficulty shifting gears, unusual noises, or leaking fluid.

If the machine doesn’t move despite engaging the transmission, it may indicate a problem. Additionally, jerky movements or inconsistent speed are indicators of a faulty transmission.

If you notice these symptoms, it’s advisable to consult a professional for diagnosis and repair. Regular maintenance and fluid checks can help prevent transmission issues.

Hydrostatic transmission lawn tractor maintenance

Maintaining your hydrostatic transmission lawn tractor doesn’t have to be a drag. Here are some witty tips to keep your ride smooth:

  1. Fluid Check Dance: Regularly check the transmission fluid level and make it a dance routine. Fluid too low? Time to raise the bar! Just remember, proper fluid levels keep your tractor grooving.
  2. Belt Serenade: Serenade your drive belt with some TLC. If it’s worn or damaged, give it the boot and replace it. A happy belt means a happy transmission, and who doesn’t love a harmonious ride?
  3. Grease Jam Session: Grease those joints like a pro musician. Lubricate all the crucial points to keep things moving smoothly. A well-greased tractor is like a jazz band—no squeaky notes allowed.
  4. Filter Comedy Show: Don’t forget to clean or replace the filters. Clogged filters can choke your transmission’s performance, and we all know a lawn tractor with stage fright isn’t entertaining.
  5. Belt Tightrope Challenge: Adjust the tension on your drive belt. It should be snug but not too tight.
  6. Cleanliness Cabaret: Give your tractor a glamorous makeover with regular cleaning. Show off that shiny paint job and keep dirt and debris from sneaking into the transmission.


What causes hydrostatic transmissions to fail?

Hydrostatic systems include mechanical components like a differential, a steering shaft, rubber and metal troughs through which the liquid moves to the desired parts. Failure of the engine hose, clogged filters, or any component can cause problems.

Do you need to change hydrostatic transmission fluid?

Usually, hydraulic fluid replacement isn’t necessary unless the drive unit also needs internal maintenance service. Also, you need to consider that this solution depends on the model of your machine, as some require more frequent change than others.

How long do hydrostatic transmissions last?

Hydraulic fluids must be changed according to the manufacturer’s service plan. With proper servicing according to our recommended servicing plan, HST transmissions should last approximately 500 hours.

Why do John Deere models have a transmission problem?

Lawnmowers equipped with hydrostatic transmission work differently. Power transfer occurs between engines and pumps. These pumps use fluid pressures when running machines. The operation of this tractor has a unique design from other lawnmowers.

Because it uses critical technology, it’s common to have transmission problems. For example, when air enters your air system, it might begin acting bizarrely. Problems with transmission systems are there because of debris or air in the system. Any foreign object in the system will cause a problem.

Why won’t my hydrostatic mower move?

The failure of the driving belt is one reason the hydraulic mower cannot move. The hydrostatic pumps depend entirely upon the transmission of electrical power by belts. You should check the belt to see that its tension is correct. You should immediately replace a worn-out belt to avoid more damage to the machine.

Final Thoughts John Deere transmission problems

The hydrostatic transmission transfers power from the motor to hydraulic pumps to run the wheels.

It’s increasingly becoming popular; it’s now used in zero-turn mowers and tractors like John Deere’s.

Like all machine parts, the hydrostatic transmission is prone to problems and we’ve discussed the common John Deere hydrostatic system problems and shared a few tips on how to solve them.

Most of the problems are easy to fix, making hydrostatic transmissions a good choice