Gearboxes in Formula 1 are not just for changing gears, but also a vital parts of the structure of the whole car which has multiple purposes like attachment point for suspension elements.
Transmission housing today are usually made of titanium and its alloys and carbon fiber and team use hybrid structures like the Mercedes W07 pictured above..
Mercedes’ transmission housing is made of titanium alloy to achieve the necessary strength, but places within carbon case to achieve desired lenght and flexibility which achieves the desired length and flexibility in suspension attachment points configuration.
Gearboxes have been for many years continue ‘spine’ on F1 car fastened behind the engine and thus contributes to the strength of the entire system. Mercedes in 2014. went a step further with their championship winning W05 Hybrid and introduced the carbon fiber shell that is not considered as gearbox and can be changed as as often as necessary, not every six race as is the case with the gearbox itself.
Also, carbon armor helps protect transmission from shocks and vibrations and can be separately replaced without penalty.
Gearboxes, their casings and shields serve to prolong the cars to the desired length (to achieve desired wheelbase), as well as being pickup points for the rear suspension, rear wing and rear crash structure.
Also, note that the rear end of gearbox structure is pointing upwards in order to free up as much space as possible for a large diffuser which can produce more downforce.
Inside the metal case of the transmission is special oil, different than the anyl other oil located in the car, the oil pump and the cooling pipes connected with the oil cooler.