The Mechanical Maniacs gained this armour at the end of Series 2. In the series finale they faced the threat of Unicron. Using various elements they had collected to rebuild Gamma they rigged their base, the Technodrome, to launch at the monster planet and explode within him. Since their technology was greater than that of the 80's - when Unicron was first made - their plan succeeded in destroying him (for a time). As one of the elements was a Transmetal Driver the resulting shockwave hit the Mechs and gave them Transmetal armour.