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What Is a Hydrostatic Transmission?

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  • Written By: Lori Kilchermann
  • Edited By: Jacob Harkins
  • Last Modified Date: 07 April 2014
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    Conjecture Corporation
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A hydrostatic transmission is a one that is operated by hydraulics. There are no provisions for a clutch or a need for changing gears with this kind of transmission. To change speeds with this type of transmission, 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. 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.

There are distinct advantages and disadvantages in the use of a hydrostatic transmission. Ease of operation is an advantage. By eliminating the clutch pedal, the machine becomes much less complicated to operate. The vehicle's speed and power can be easily controlled with the speed and direction lever instead of the throttle. The engine can also be used to control the descent down a hill or grade by using speed and direction rather than the brakes.

The hydrostatic transmission also has its share of faults. First, the hydrostatic transmission increases the odds of becoming stuck. The power application often directs far too much torque to the wheels in a soft terrain situation, making them prone to spinning and becoming stuck. Also, the tire speed is not as effectively managed as by a throttle, creating a control issue that typically results in the operator losing the fight between gravity and soft surfaces.

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This type of drive system is also more costly than a typical clutch and gear operated transmission. The hydraulic fluid alone that is used in a hydrostatic drive vehicle is more expensive than a clutch unit in a traditional transmission. Maintenance and service is far more costly with a hydrostatic drive transmission, making the use of a traditional clutch much more attractive to many buyers.

For most hydrostatic transmission owners, the thought of going back to a traditional transmission is not one worth discussing. The ease of use of the hydrostatic transmission makes short work of many tasks and allows the operator to perform a job more comfortably than 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.

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Discuss this Article

anon936812
Post 3

I would like to know if a "Hydrostatic transmission" would work for a golf cart application?

Wisedly33
Post 2

@Lostnfound: Actually, most of the vehicles that have hydrostatic transmissions are heavy duty vehicles like tractors, rather than passenger vehicles. The thinking is that this kind of transmission is not very efficient on the street at high speeds. Not sure why, but I'm no engineer!

Lostnfound
Post 1

I know I've heard the term "hydrostatic" when referring to a transmission, but I didn't really know what it meant. I figured with the "hydro," it had something to do with hydraulics, but beyond that, I didn't know what it was. I sure didn’t know the difference between a regular transmission and this kind.

I would be interested in knowing what kinds of cars have these transmissions. I'm sure they're way out of my price range, but I'd still be interested in seeing which cars carried them. I suspect they all have European labels on them and are probably manufactured by hand in a small, rural factory.

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