If an excavator's swing brake is dragging, it will cook the swing motor oil and cause the machine to slow down. But how do you tell if the brake is dragging if you don't have a pressure gauge to test the pilot release circuit? There is an incredibly simple, no-tools field test called the "Coast-Down Test."
First, make sure the machine is on flat, level ground with no personnel nearby. Start the machine and let the hydraulics warm up. Swing the house to the left or right at a moderate speed, then release the swing joystick abruptly. Watch the side of the cab or the boom to see how quickly the machine stops.
A healthy swing brake should allow the machine to coast slightly-maybe 15 to 20 degrees-before the brake springs engage and lock it solid. If the machine stops instantly the second you let go of the joystick, like it hit a brick wall, the brake discs are dragging. The friction is actively slowing the swing down before the brake even fully engages.
To confirm, do the "Hot Hand Test." After doing a few continuous 360-degree swings, shut the machine down and carefully touch the aluminum housing of the swing motor. If it is too hot to keep your hand on for more than a second, the brake is definitely dragging. A properly adjusted brake should only get warm, not scalding hot. If it fails either test, the brake pack needs to be pulled, inspected for glazed friction discs, and the pilot release pressure needs to be checked. Running a machine with a dragging swing brake will eventually weld the friction discs to the steel plates, locking the machine in a permanent straight-ahead position.
