air was filtered by bubbling it through a water tank. On dry days, mud would build up in the water tank after a few of hours of operation. The mud would then have to be flushed out and the tank refilled. Reliability and roll-overs The Fordson Model F was not without flaws it shared with other brands. These problems included practical limits to traction, especially under muddy, snowy, or icy conditions, and the habit of rearing over backwards if the plow encountered an obstruction. Many people complained that the traction would be better if the tractor were heavier, although Henry Ford always countered that merely adding weight was not a smart way to maximize traction. Ford began shipping Fordson tractors to Ford Motor Company Limited in Britain in 1917 to meet an order from the British government for 5,000. Between the time the order was accepted and when production started, Ford overhauled the design to solve several problems. The car-type radiator was enlarged to capacity to cure overheating problems. The additional weight also helped hold the front down. In early Fordsons, the drive worm was located at the top under the driver's seat. During heavy operation the heat became unbearable to the operator. The drive worm was relocated to solve this problem and also allowed larger rear wheels which improved traction. Several changes were also made to simplify manufacture. The Fordson used the Model T coil magneto system; and water and oil pumps were eliminated in favor of the simpler thermosiphon cooling and splash lubrication. Despite design and assembly improvements, Fordsons still required a high level of maintenance. A farmer near Atlanta in 1921 listed the cost of his Fordson repairs for the year as $1,246. He recorded problems in his diary, noting difficulty starting the engine, a broken wheel, engine failure and the rear end bursting throughout January, totaling costs of $1,301 for 620 hours of work. A Colorado farmer telephoned his dealer three times a day to complain about his Fordson. The most dangerous problem occurred when a towed implement became immoveable: the stoppage of the implement would cause a reaction through the transmission that would flip the tractor over backwards, sometimes killing the driver. This condition was caused by the low-geared worm drive, light weight and short length, so that there was insufficient downward load to counter the reaction torque. The cause is sometimes said to have