The early models had "Speed Trims" were electric actuators that tilted both Rotors forward as Air Speed increased from 60 knots in order to level the fuselage and reduce drag. As the airspeed decreased the actuators reversed that input.
If the Speed Trims stayed extended....and the aircraft slowed it put excess strain on the Aft Vertical Shaft that connected the Aft Transmission to the Aft Rotor Head.
There were Manual Switches for use in that case that allowed the Pilots to manually retract the Speed Trims.