What Is a Power Shift Transmission on a Tractor?

Transmissions vary in terms of cost, durability, and applications. Different designs transfer engine power to the wheels in various ways.

A more recent advance is the power shift transmission, which allows you to change gears on the run, under various loads. Traditional manual and hydrostatic transmissions still have their place, but power shift transmissions are an ideal choice for the right applications.

Types of Tractor Transmissions

Tractor transmissions range all the way from traditional geared speed to power shift designs. They vary in cost, and are engineered for the wide variety of circumstances under which different sized tractors must perform. Learn what these different Kubota tractor transmission types mean.

Geared speed

The low-cost constant mesh design requires you to stop the tractor to shift gears. A synchromesh transmission operates much like a manual on a passenger vehicle – it allows you to shift gears on the go.

Power shuttle

About 20 years ago, the power shuttle transmission arrived. It replaces the traditional foot clutch with a forward-reverse lever on the steering column that operates a wet clutch. It’s useful when there’s a great deal of forward-reverse shifting, such as with loader work.

Hydrostatic

Hydrostatic transmissions are commonly used in riding lawn mowers and low-power tractors. Hydraulic oil under high pressure spins the shaft that drives the wheels. The pedal-operated design typically offers 2-3 ranges with speed regulated by RPMs.

CVT

Belt-driven continuously variable transmissions (CVTs) efficiently transfer power to the wheels using an infinite number of speeds. CVTs are good for tilling and other activities that require ground engagement.

What is a Power Shift Transmission on a Tractor?

The tractor power shift transmission is an ideal choice for several applications. With a full power shift transmission you can shift through all gears without clutching. A semi-power shift is a transmission that can be shifted two or more speeds without clutching, although it must still be clutched to shift ranges.

How does a power shift transmission work? Typically, a power shift transmission makes use of multi-plate wet clutch packs. Each clutch pack is composed of a stack of clutch discs that can be pushed together via a hydraulically driven piston. A spring or springs release the piston when the hydraulic pressure is off. Some clutch packs use the hydraulic pressure and springs in reverse, with the springs applying the pressure and the hydraulics releasing the pressure.

Power shift transmission operation is like a collar shift transmission, except clutch packs are employed rather than collars. The clutch packs lock the desired gear onto the transmission’s rotating shaft. You do not need to use the clutch for directional changes as well as some gear changes.

To shift gears, hydraulic pressure is applied via an electric solenoid or mechanical valve. The power shift concept is very versatile because it is possible to design the transmission with many speeds by using multiple clutch packs for every speed.

Power Shift Transmission Operation

The transmission operates within a range. For example, some designs offer four speed ranges (slow to fast) selected through the use of a lever. A semi-power shift design makes use of a clutch to move from one range to another.

Within these ranges is a choice of four to six speeds. For example, a 4-range transmission with a 6-speed power shift would offer 24 speeds. When the speeds also operate in reverse, you have a 24×24 power shift transmission.

With a power shift transmission, the operator selects the RPMs and appropriate gear for the job. When the load on the tractor increases and RPMs drop, the operator manually changes gears.

The power shift transmission is popular for use with front-end loader work and other tasks performed under load. Geared speed, hydrostatic and CVT transmissions all still have their place, depending on your budget and applications.

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Bobby Ford Tractor and Equipment is your Greater Houston Area Kubota dealer. For professional and knowledgeable sales and service, please contact us online today. Or, visit us to check out our complete line of Kubota Tractors.