Hydrostatic Drive


The hydrostatic transmission is a closed-loop circuit, where the fluid exiting from the drive motor outlet is returned to the hydrostatic pump without being sent to the tank. In this circuit, the input drive is the hydrostatic pump connected to the prime mover, and the output drive is the drive motor which is connected to the load. John Deere LT166 LT155 OEM Tuff Torq Hydrostatic Hydro Drive Transmission. John Deere Hydrostatic Transmission LX277AWS LX279AWS LX280AWS AM123276 K62B. Hydro-Gear ZC-DPBB-2M5A-2WPX OEM Left Hydrostatic Hydro Transmission -M5.

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Combustion engines, like those found in most cars, transfer power to the vehicle’s axle, which turns the wheels. Hydrostatic transmissions found in most modern tractors and zero-turn mowers, work by transferring power from the engine to hydraulic pumps which use liquid pressure to move the wheels. There’s no need for gears, and changing speed is smooth and efficient.

With any transmission, things can go wrong. The first step is to read your Operator’s Manual. There are many different types of equipment with hydrostatic transmissions, and we can only offer general advice. Your tractor operator’s manual will have information specific to your make and model, and will offer helpful information about where to find filters and other parts that might require servicing are located on your tractor or lawn equipment.

Where to find more information:

Hydrostatic Drive Motors

Hydrostatic transmissions include mechanical parts such as a differential and a drive axle, plus rubber or metal hoses the liquid is pushed through. Failure of any mechanical component, a broken hose, or clogged filter will cause tractor hydrostatic transmission problems. But the most common issue will be the oil itself.

In the transmission section of your operator’s manual, you’ll find a section that covers oil viscosity. Here’s an example from a John Deere manual. Note that, while temperature affects viscosity, the right oil has enough range to operate in any reasonable weather.

Here are some basic troubleshooting tips to fix your hydrostatic transmission lawn tractor problem fast!

1. Zero-Turn Mowers: Purge Your Hydraulic Drive System

Zero turn hydrostatic transmission problems can start with air in the system, a condition known as cavitation. When the pump is full of air instead of oil, it can’t generate the pressure needed to provide power. This is pretty common in zero-turn mower transmissions. After your mower has been stored for the winter, it’s a good idea to purge the transmission before use. It’s also a good first step if your motor is sluggish or slow.

NOTE: If your mower or tractor has a transmission that must be removed for service, be sure to purge after it is serviced and before you use it.

Hydrostatic drive bypass control
  1. Park the mower on level ground, set the parking brake, and put the rear on jackstands.
  2. Make sure the oil reservoir is properly filled according to specs.
  3. Disengage the transmission (check your operators manual to see how this is done).
  4. Sit in the operators seat and start the engine.
  5. With the engine running, move throttle control to slow position. Position the motion control levers in neutral (N) and disengage clutch/brake pedal.
  6. Push motion control levers forward all the way and hold for five seconds.
  7. Pull motion control levers to full reverse position and hold for five seconds.
  8. Repeat steps 6 and 7 three times. This purges any air from the hydraulic transmission system.
  9. Put the control levers in neutral (N). Shut the engine off and set the parking brake.
  10. Check the oil and top off if necessary.
  11. Engage transmission.
  12. Remove from jackstands, start the engine, and disengage the brake.
  13. Move control levers forward and roll about 5 feet. Then slowly reverse about the same distance. Return the levers to neutral and repeat this steps three times.

You’re done! The air is purged from your system and your zero-turn mower is ready for action.

2. Check The System

If your system is purged and you still have a problem, it’s time to do a little basic troubleshooting. Start with a complete visual check of the hydraulic system.

Hydrostatic Drive Problems

  • Check the oil level and add oil if needed.
  • Inspect the hoses and connections for damage or signs of leaks.
  • Clean pump cooling fins with a rag, brush, or compressed air, and check for damage.

3. Change Your Hydraulic and Steering Fluids

Sluggish operation is often due to old or overused fluids. If there are no signs of fluid leaks or damage, it may be time to change your hydraulic and steering fluids.

4. Hire An Expert Troubleshooter

If you need help troubleshooting your tractor’s hydraulic system, call your dealer. Their service department should be able to ask the right questions, give suggestions, and you can make an appointment for service if necessary.

Hydrostatic drive system kits

Call or visit us:

Blairsville, GA: 706-745-2148


Jasper, GA: 678-454-2900

Hydrostatic drive motors

Some things are beyond DIY. When it’s time to call in an expert, don’t hesitate. Your tractor represents a significant investment in terms of both money and delay. It’s one of those farm equipment essentials you simply can’t do without. When it needs to be fixed fast and done right, call an expert!

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Image source: Z915E ZTrak Zero-Turn mower with hydrostatic drive train, deere.com

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Hydrostatic transmission is a category of engine mechanics, and basically describes a system in which power is generated and transmitted by pressurizing and releasing fluid through specialized pumps. It’s also sometimes called “continuously variable transmission,” and it works by converting energy harnessed from the movement fluid through hydraulic pumps to the drive train of a vehicle. This sort of transmission can technically be used to power almost any type of machine, though it’s most commonly seen in heavy-duty machinery like tractors and backhoes. The transmission has the ability to provide a lot of power very quickly, but it isn’t usually very efficient when it comes to acceleration and maintaining high speeds. As such, it isn’t usually a good choice for passenger cars or trucks that spend most of their time on the highways.

How it Works

Motor vehicle engines usually come in several different types, and in most cases they’re named based at least in part of how they work. Passenger cars, for instance, are typically marketed with either “automatic” or “standard” transmissions, and both are terms that describe how the technology works — which is to say, whether the engine gears will shift automatically in response to driver speed, or whether they require driver engagement. Describing an engine as having a hydrostatic transmission is usually a statement about how the engine actually operates internally. In these cases, fluid is transferred from a piston pump to the motor through a series of tubes, and the energy generated in the process is what actually powers the vehicle.

There are no provisions for a clutch or a need for changing gears with this kind of transmission. To change speeds the operator simply moves the speed selector in the direction that represents the desired reaction. Typically, the farther forward the speed selector is pushed, the faster forward the tractor or vehicle will go, while pulling the lever to the rear while in motion will allow the vehicle to slow down. From a stopped position, pulling the lever backward places the vehicle in reverse.

Hydrostatic Driveline

Most Common Applications

This sort of transmission works really well for machinery that needs to have a lot of power without a lot of movement. Most machines that use it also have big enough engine boxes to hold its typically large size; it’s common in land-moving equipment and industrial machinery, particularly tractors, excavators, and forklifts. Anything that needs a lot of power and energy in short bursts can usually benefit from this sort of energy arrangement, though it’s not usually a good choice for vehicles that need speed. This includes cars, trucks, and equipment that needs to move in traffic.

Hydrostatic Drive Motor

Why People Want It

Ease of operation is one of the biggest advantages to hydrostatic transmission. By eliminating the clutch pedal, the machine becomes much less complicated to operate. The vehicle's speed and power can be easily controlled with levers instead of a throttle, too, and the engine can also be used to control the descent down a hill or grade by using speed and direction rather than brakes.

This sort of transmission also makes certain jobs more efficient, and may allow the operator to get work done more comfortably than with the tiresome pushing of the clutch and the changing of gears. Once acclimated to the hydrostatic drive, most operators are able to manipulate the machinery with one hand without ever touching the throttle or the braking system until finished with the task.

Drawbacks and Disadvantages

The hydrostatic transmission model isn’t without its faults, though. The mechanics involved in transferring power from the hydraulic shafts to the to gearbox increases the odds of something becoming stuck. The power application often directs far too much torque to the wheels in a soft terrain situation, making them prone to spinning; also, in most cases, the tire speed is not as effectively managed as by a throttle. This can create a control issue that typically results in the operator losing the fight between gravity and soft surfaces.

Hydrostatic Drive Problems

Hydrostatic drive car

Expense might also be a factor. Hydraulically powered drive systems tend to be more costly than more typical clutch and gear models. The fluid alone is often pricey to buy, and maintenance and service tends to be a lot more expensive, too. For these reasons, some people choose traditional clutch transmission systems for their machinery, particularly if it’s something that’s only used sometimes or for limited projects.