An apparatus for spring-assisted pivoting a liftgate or door against gravity between a closed position and an open position includes a torsion bar spring system with springs arranged in parallel in a meander pattern and connected with one another in fixed rotative engagement. An outer bearing-torsion bar spring and another outer lever-torsion bar spring are each supported in a support bracket of a tracker. The lever-torsion bar spring is connected in fixed rotative engagement with a length-adjustable lever guided in a control cam of the tracker. A coupling rod configured for translatory movement engages with the length-adjustable lever for rotating a hinged lever associated with the liftgate or door. An adjusting device is connected with the bearing-torsion bar spring in fixed rotative engagement and can be variably locked relative to the support bracket. A method for producing such apparatus is also disclosed.