releasethehandbrake (third-person singular simple presentreleases the handbrake, present participlereleasing the handbrake, simple past and past participlereleased the handbrake)
(figurative) To let go; to stop an internally imposed restraint.
2020 October 14, Phil McNulty, “England 0-1 Denmark: 'Harry Maguire looked devoid of confidence in Nations League loss'”, in BBC Sport:
As the game went on, Southgate still seemed very reluctant to release the handbrake, even taking the fact England were down to 10 men into account.
Used other than figuratively or idiomatically:seerelease,handbrake.