A wheel loader was brought in with a terrifying symptom. It had zero drive power. The engine ran perfectly, the transmission shifted into gear, but the machine would barely move, as if the parking brake was on. The operator confirmed the parking brake switch was off.
We put a flow meter on the transmission and found the torque converter was stalling out at a very low RPM, indicating a massive mechanical load on the drivetrain. We jacked the front axle off the ground. The wheels would not spin by hand. The brakes were locked on, hydraulically or mechanically.
This machine used enclosed, wet disc brakes. They are applied by heavy spring pressure and released by hydraulic pressure. We removed the brake housing and found the root cause. The brake housing had a weep plug on the bottom that had never been cleared. Water from pressure washing and deep mud had seeped into the housing and filled the cavity around the spring pack. Over the winter, the water rusted the heavy coil springs solidly to their mounting plates. The springs were completely seized in the "applied" position. When the operator activated the brake release hydraulic pressure, the piston pushed against the springs, but the springs couldn't compress because they were rusted solid. The brakes remained clamped. We had to physically cut the springs out with a grinder, clean the rust, and install a new spring pack to free the machine.
