The Mason Bogie was still, though, plagued by one of the biggest problems of the Fairlie - the jointed steam pipes to the driven truck leaked far too much steam. Mason eventually changed to a different scheme, in which the pivot point for the leading truck became a hollow ball joint through which the live steam for the cylinders passed. Mason also developed a sliding seal for the exhaust from the moving cylinder saddle into the smoke box. Although better, Mason's improvements took up much valuable space in between the driving wheels, forcing Mason to use an outside valve gear, generally the Walschaerts valve gear. Additionally, the reversing shaft had to be mounted atop the boiler, with a long lifting link dropping down to the radius rod, a feature unique to Mason Bogies (this was necessary because the lifting link would swing to the side as the truck pivoted, lifting the radius rod and changing the valve setting. Lengthening the link, and thus increasing the radius of its swing, minimized the amount of change.).