Variable length shaft and method for making the same

The present invention relates generally to mechanisms which allow for length adjustment of shafts or rods, and more particularly to mechanisms using a rheological fluid to perform the releasing and locking functions. Such mechanisms can be used in various applications, including headrests, steering columns and seats. A variable length shaft is provided including a housing defining an internal space. A shaft is connected to a plunger device disposed in said internal space. The internal space is filled with magneto-rheological fluid which is selectively provided with a magnetic field for solidifying the fluid to prevent movement of the plunger within the internal space. When the magnetic field is removed, the plunger device moves freely for allowing variation in the length of the variable length shaft system.