[Kevin Sevcik]

Brake mode won't help unless they've removed the anti-backdrive pins from the window motors. Brake mode only engages when the motor is stopped, which is when the anti-backdrive pins also kick in. The fundamental issue is that the arm still isn't perfectly balanced and is still falling under its own weight. As long as that's the case, your arm is going to go down faster than up, because more torque is required to lift the arm. You're never going to completely even things out with surgical tubing either. If you arrange it and tension it to balance things when the arm's level, it's either going to pull too hard when you lower the arm below level or raise it above level. So if your arm works reasonably now, I recommend leaving well enough alone.

For the curious, the best bet for perfectly balancing it would be an actual counterweight on the arm, followed by a constant force spring mounted a reasonable distance from the pivot so the spring is always approximately vertical. But either is loads heavier and more complicated than some surgical tubing.