Sudden stark terror etched on the faces of CATE BLANCHETT and ROONEY MARA shocked a camera crew filming the stars as they drove a classic 1950s Dodge down an icy Cincinnati road for their new flick “Carol” when, in a classic unscripted moment, the brakes failed – and both women shrieked!

Reports my on-set source: “Cate was driving and everything was fine until she tried to stop the car…and the brakes failed! She kept pumping the pedal as fast as she could, but nothing happened! The girls started screaming at the top of their lungs, speeding past the film crew, who’d pulled to the side of the road after they’d finished shooting!”

Desperate to stop the runaway car, Cate suddenly jerked the wheel hard right.

“It spun around on the icy street, but finally came to a halt as it slammed into a wooden fence. Everyone came running, expecting to find Cate and Rooney seriously injured – or worse – but as a camera guy started dialing 911, he heard Cate yelling, ‘We’re OKAY…! We’re good! The car isn’t good, but we’re fine!’”

Visibly shaken, she and Rooney were helped out of the sturdy old Dodge as the relieved director told them they’d filmed a perfect take – so the ladies got the rest of the day to recuperate.