Abstract: A very heavy vehicle may tend to run away on a steep gradient and as a result the engine is liable to be overspeeded with consequential risk of damage especially to its valve mechanism. The invention aims to prevent overspeeding by providing a servo mechanism operable automatically above a predetermined engine speed to apply an exhaust brake. The servo mechanism preferably comprises a centrifugal clutch normally held disengaged by springs and disposed on a shaft driven by the engine. Angular movement of the driven member of the clutch due to its engagement by engine speed in excess of the predetermined value is limited to, say, 60.degree. by a stop, and said member is mechanically linked to the operating means of the exhaust brake.

Abstract: Epicyclic gearing comprises a sun gear journalled on a shaft and meshing with a plurality of planet pinions which mesh also with a rotationally fixed annular gear, the pinions being journalled in a planet carrier having a floating driving connection with a sleeve rigidly secured on the shaft by splines and a lock-nut, the floating connection including respective sets of external gear teeth on the sleeve and the lock-nut and two sets of internal gear teeth on the planet carrier which mesh with the respective sets of external gear teeth, and the tip diameter of one set of teeth on the planet carrier being greater than the tip diameter of the teeth on the lock-nut.