We have developed a new, three dimensional vocal tract mechanical model for an anthropomorphic talking robot WT-7R (Waseda Talker No. 7 Refined), to improve the resonance of the vocal tract. The Waseda Talker robot series aims to reproduce the human speech mechanism with three-dimensional accuracy. The tongue of the previous model, WT-7 (Waseda Talker No. 7), was made of rigid links and covered with a thermoplastic rubber (Septon). This mechanism could deform the tongue shape and work as a part of the vocal tract, however, the cover thickness was not sufficient enough to prevent sound leakage, and did not have sufficient resonance. As a result, the produced sounds were unclear. To resolve this problem, the inner area of the tongue was filled with liquid. We experimented to select the filling liquid which is minimizes damage to the Septon cover and provides adequate resonance characteristics. The ethylene glycol was selected because it does little damage to the Septon and is relatively non-flammable. An oil seal and liquid gasket prevent leakage into the robot. WT-7 also has problems with its tongue link deformation range and open lip control range - these problems were also addressed. The improvements made the vowel production of WT-7R clearer than that of the previous robot, and the bandwidth of the formant peak in spectral analysis became sharper.