Cessna 421 pilot reported a loss of control to steer or stop the aircraft on the ground; due to a malfunction of the brakes and rudder steering; resulting in a taxiway excursion. The aircraft collided with a runway sign off the taxiway; collapsing the nose gear; and the pilot evacuated without injury.

Narrative

On Day 0 Aircraft X was release from maintenance for work done on the alternate air valve ; alternator; starter; and battery replacement. I the pilot in command and the sole person onboard was suppose to depart ZZZ destined for ZZZ1. At approximately XA:10 Aircraft X was started;initial routine checks her made to ensure flight control were free and correct which all seems to pass the test at the time. Upon taxiing out to hold short of runway XX where the final run up checks were going to be performed before departure the pilot tried to apply the right rudder pedal in combination with the right brake to make a slight right to align the aircraft with the hold short bars . In trying to do so it noticed an apparent loss in effectiveness and ability to steer right. In an attempt to stop the aircraft both brake pedals were applied which turn out to fail in the moment. To prevent extensive damage to the aircraft and myself i completely secured both engines as the direction of the airplane was headed straight for the runway marking signs which could not be prevented due to no brake or rudder. Being unable to steer the aircraft away from the objective the nose gear collided with the runway sign which resulted in the nose gear retracting and nose of the aircraft plowing into the grass. i proceeded to secure the aircraft by switching off all the electrical components and exiting the aircraft where further assist was called for. Extensive damage however was sustained to the nose landing gear and fortunately no injury sustained to the pilot in command.