A gearbox having an integral wet brake assembly is provided to replace the prior gearbox assembly of an underground mining machine. The brake housing is configured and contoured to be nestingly received upon the gearbox housing and without intrusion upon the output drive flanges. The brake housing includes concentric parking and service brake pistons adapted to engage and disengage a brake disc stack provided within a cavity machined into an end plate of the gear box assembly. An intermediate shaft of the gearbox is provided with a hub to engage the rotary discs of the brake disc stack. The parking brake is normally engaged by a spring and released by hydraulic pressure, while the service brake is normally released by a spring and engaged by hydraulic pressure.