He installed a necker's knob to make steering easier.
necker's knob
idiomSynonym of Brodie knob.
Origin
disputed originFrom the humorous portrayal of the knob's purpose as being that it helps the driver to steer with one arm so as to leave the other arm free to provide romantic attention to a companion.
The driver attached a necker's knob to the steering wheel to help him maneuver the heavy truck through tight city streets.
While the vintage tractor lacked modern power steering, the addition of a worn necker's knob allowed the farmer to navigate the uneven fields with surprising precision.