We want to share important information that will give you excellent insights into the various tractor transmission types and their history.
And as a quick aside --- we are here to help you purchase a new tractor, parts, and implements when the time is right.
Let’s dive into the details.
Introduction
Most older farm tractors use a manual transmission with several gear ratios --- typically three to six --- sometimes multiplied into two or three ranges.
This arrangement provides a set of discrete ratios that combined with the varying of the throttle, allows final-drive speeds from less than one up to about 25 miles per hour (40 km/h).
Operating Speeds
The lower speeds are used for working the land and the highest speeds are used on the road.
Slow, controllable speeds are necessary for most of the operations performed with a tractor.
They help give the operator a degree of control in certain situations --- such as field work. When traveling on public roads, the slow operating speeds can cause problems, such as long queues or tailbacks. These can delay or annoy motorists in cars and trucks. These motorists are responsible for being duly careful around farm tractors and sharing the road with them, but many shirk this responsibility. So various ways to minimize the interaction or minimize the speed differential are employed where feasible.
Some countries (for example the Netherlands) employ a road sign on some roads that means "no farm tractors." Some modern tractors, such as the JCB Fastrac, are now capable of much higher road speeds of around 50 mph (80 km/h).
Designs
Older tractors usually have unsynchronized transmission designs.
They often require the operator to stop the tractor to shift between gears. This mode of use is inherently unsuited to some of the work tractors do today. Luckily, it has been circumvented in various ways over the years.
Shifting
For existing unsynchronized tractors, the methods of circumvention are double clutching or power-shifting --- as both require the operator to rely on their skill to speed-match the gears while shifting.
They are undesirable from a risk-mitigation standpoint because of what can go wrong if the operator makes a mistake. Transmission damage is possible. Loss of vehicle control can occur if the tractor is towing a heavy load either uphill or downhill.
The operator's manuals for most of these tractors state that an operator must always stop before shifting. They do not mention the alternatives. That mode of use is inherently unsuited to some of the work tractors do --- so better options were pursued for newer tractor designs.
CVTs (Continuously Variable Transmissions)
Unsynchronized transmission designs were replaced with synchronization or with continuously variable transmissions (CVTs).
Either a synchronized manual transmission with enough available gear ratios (often achieved with dual ranges, high and low) or a CVT will allow the engine speed to be matched to the desired final-drive speed while keeping engine speed within the appropriate speed (as measured in rotations per minute or rpm) range for power generation (the working range) (whereas throttling back to achieve the desired final-drive speed is a trade-off that leaves the working range).
Modern Age
The problems, solutions, and developments described here also describe the history of transmission evolution in semi-trailer trucks.
One major difference is the fleet turnover. Most of the old road tractors have been scrapped and many of the old farm tractors are still in use.
Therefore --- old transmission designs and operations are primarily just of historical interest in trucking --- whereas in farming it still affects daily life.
Hopefully, this brief article has helped you better understand the evolution of tractor transmissions.
If you need any further help or have any questions about transmissions, tractors, implements, or anything else equipment-related, please contact your dealer, local mechanic, or call us at 602-734-9944. Please ask about our current new and used tractor supply.
If you are looking for old, vintage, classic, or new tractor parts, send us a part request.
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