A wheel loader was brought in with a maddening symptom. It operated perfectly fine on flat ground, but the moment the operator drove down a slight incline-like into a gravel pit-the hydraulic pump would let out a loud, agonizing whine, the boom would lose all power, and the steering would go completely stiff. As soon as the machine was leveled out, the hydraulics worked flawlessly.
The shop assumed the pump was cavitating due to a restricted suction line and replaced the main pump. It didn't fix the issue. We inspected the suction hose and found no collapses. The problem was hidden inside the 80-gallon hydraulic reservoir.
Modern hydraulic tanks have internal baffles-metal plates that run vertically inside the tank. Their job is to slow the oil down, force it to travel a longer path to cool, and prevent the aerated return oil from being immediately sucked back into the pump. We drained the tank and removed the top inspection plate. The internal baffle had cracked its welds and broken completely loose.
When the loader was on flat ground, the baffle rested harmlessly at the bottom of the tank. But when the machine drove down an incline, the oil surged forward, carrying the heavy steel baffle with it. The baffle slid forward and slammed directly against the internal suction strainer, completely blocking the pump's access to the oil. The pump starved instantly, causing the whine and the loss of function. When the machine leveled out, the oil settled and the baffle slid back, opening the suction port. We rewelded the baffle to the tank wall with heavy gussets, and the phantom cavitation vanished.
