Even the most experienced driver might climb into a tractor cab for the first time and find the array of knobs, switches and levers confusing. They’d also be forgiven for spotting extra pedals on the floor and wondering what on earth they’re all for. Whenever someone gets on a tractor for the first time, they’re first question is often why do tractors have two brake pedals?
Why do tractors have two brake pedals?
The short answer to the question ‘Why do tractors have two brake pedals?’ is this: they’re independent brakes. When you press the brake pedal in your car, all the brakes connected to that pedal operate evenly on every wheel. This means the braking force acting on every wheel is the same. If a vehicle ever needed different amounts of braking to be applied to different wheels, it would need to be equipped with independent brakes.
So what are independent brakes?
Independent brakes allow the driver to apply different amounts of braking to different wheels. Tractors usually have brakes only on their rear wheels, which are also the main driving wheels. As there is one brake on each wheel, there are two brakes, which is why tractors have two brake pedals.
When would a tractor driver need to use independent brakes?
The earliest examples of independent brakes on tractors were called steering brakes. For example, when the driver pressed the left brake pedal, they’d apply the brakes only to the left wheel. The right wheel will continue to drive as normal, which forces the tractor to veer to the left.
Normally the tractor driver will just use the steering wheel if they simply want to turn left. However if they’re making a tight manoeuvre and are already at full lock, the independent brake can help the tractor turn extremely tightly. It’s best practice to use this option scarcely. As braking hard will probably lock the wheel, the tractor will either be wearing excess rubber off of the tires or tearing into the surface of softer ground.
When you have to steer with the rear wheels
Even experienced tractor drivers will take or for granted that moving the steering wheel will turn the tractor. However if the front wheels don’t have good traction, the steering wheel isn’t an awful lot of help. This often happens when the weight of an implement carried on the back of the tractor, and therefore behind the rear axle, lifts the front of the tractor.
With a heavy link box and a few sheep behind the rear wheels, the front of this Fordson Dexta will lift easily.
This was a common occurrence with early two-wheel drive tractors. They were so light in the front-end that they’d often lift, leaving the driver with only the independent brakes to control the steering. Nowadays, tractors are usually four wheel drive and have bigger more powerful engines. This means more metal and more weight in front of the back axle. Front weights are also widely used to add traction to the front axle, so it’s far less common to use the brakes for regular steering.
Surprising uses for independent brakes
The whole point of tractors is traction. They often rely on four-wheel drive for extra grip on soft ground. For many years, tractors have also been equipped with diff lock to stop the open differential from letting the rear wheels receive different amounts of drive. Vehicles are equipped with differentials so that the wheels can move at different speeds.
This is essential for turning because it means that the wheel on the outside of the turn can rotate more than in the inside wheel. It needs to rotate more because it travels a greater distance than the inside wheel. Conversely the inside wheel needs to travel a shorter distance and therefore slower. Without the differential, the inside wheel’s tyre would wear excessively and also send stress back into the drive system.
The issue with differentials is when one of the driving wheels loses grip. The differential allows this wheel to spin because it’s easier for the vehicle to send drive to the wheel that’s not gripping. Diff lock forces the drive to go to both wheels equally, meaning the wheel that has grip helps the vehicle move.
Tractors have always had differentials, but they haven’t always had diff lock. Many early two-wheel drive tractors lacked diff lock and often lacked traction too. When one of the wheels started spinning on one of these tractors, like the Fordson Dexta above, the driver could gently apply the independent brake to the wheel that’s spinning to get moving again.
It sounds counter intuitive at first, but remember that the wheel is spinning because it’s easier for the diff to send drive to the slipping wheel than to the other wheel. Therefore by applying the brake to the spinning wheel, this puts load on the differential which makes it send drive to both wheels more evenly. The result is the gripping wheel gets moving again and the tractor moves. Modern traction control units work in a not dissimilar way.
Have tractors always had two brake pedals?
Tractors haven’t always had two brake pedals but they certainly have for a very long time. The earliest example was the Ferguson Brown Model A, which was equipped with so-called ‘steering brakes’. It took just a few more years for the twin-pedals we’re now used to to became commonplace. By the 1950s, twin brake pedals were the norm and many earlier tractors were equipped with independent brakes in this way.
By the 1950s, it was normal for tractors to be equipped with twin brake pedals, like this 1958 Allis Chalmers D272.
Why do tractors have two brake pedals when some don’t have independent brakes?
Taking the tractors that were simply too early as read, there are still rare exceptions where tractors don’t have independent brakes at all. The most high profile examples would be the JCB Fastrac models, which have just one brake pedal. These differ in many ways from conventional tractors, particularly with their features that make them well-suited to road work.
Later models are equipped with anti-lock brakes on all four wheels and can achieve relatively high top speeds. As steering with brakes is a bad idea on the road, the Fastracs aren’t equipped with two brake pedals. Instead, the Fastrac has four wheel steering options to help with manoeuvrability. To ensure tractors with independent brakes are safe at road speeds, the twin pedals are equipped with a bolt or lock so that touching either pedal moves both pedals equally.
Summary: Why do tractors have two brake pedals?
- Tractors have two brake pedals because they are equipped with independent brakes
- Tractors typically have two brakes, one left and one right on the rear wheels, each controlled by one of the two brake pedals
- Independent brakes can be used to steer, either for making the tractor turn more tightly or to turn when the front wheels don’t have a good connection to the ground
- Independent brakes were also used to help regain traction before tractors were more widely equipped with both diff lock and four-wheel drive
- Independent brakes are linked together when travelling on the road to stop dangerous changes of direction when breaking at road speeds. Some models designed with road work in mind like the JCB Fastrac don’t have independent brakes
So next time someone asks you ‘Why do tractors have two brake pedals?’, you can tell them why! For more blog posts about tractors, take a look at my Farm Museum posts.