A mucking loader that suddenly becomes slow and weak can ruin your entire tunneling or mining shift. Instead of powerful digging, the machine barely moves the bucket. This common problem frustrates operators and kills productivity.

If your mucking loader struggles to lift or dig, don’t immediately blame the engine. In most cases, the real culprit hides in the hydraulic system. Below, we break down the three main reasons for slow, weak digging and show you how to fix each one.

Why Your Mucking Loader Loses Digging Power
When the engine runs normally but the machine moves slowly and cannot dig effectively, the hydraulic system is likely failing. Three components cause 90% of these issues:

1. Worn Hydraulic Pump (Most Common)
The hydraulic pump is the heart of your mucking loader. Over time, internal parts like the cylinder block, pistons, and valve plate wear down. This creates internal leakage – oil slips past worn gaps instead of flowing to the cylinders and motors.

Typical symptoms:

The machine works fine when cold but gets weaker as it warms up.

All actions (lift, swing, travel) are slow together.

Metallic noise from the pump area.

Fix: Measure pump pressure and flow. If pressure drops below specifications, rebuild or replace the pump. Always change the hydraulic oil and filter after pump repair.

2. Faulty Main Control Valve (Multi-Way Valve)
The main control valve directs oil to different cylinders. If its safety valve (relief valve) setting drifts too low, or if the spool and valve body wear, high-pressure oil leaks back to the tank.

Typical symptoms:

One specific action (e.g., bucket curl) is weak while others work better.

The engine does not lug down even under heavy load.

Oil temperature rises faster than normal.

Fix: Test the relief valve pressure with a gauge. Adjust it to factory specifications. If wear is severe, replace the valve spool or the entire multi-way valve assembly.

3. Weak Pilot Pump (Gear Pump)
Many mucking loaders use a small gear pump (pilot pump) to generate control pressure for the main valve. When this gear pump wears out, it cannot produce enough pilot pressure to fully open the main valve spools.

Typical symptoms:

Lever movements feel light or unresponsive.

The machine reacts slowly even when you move the joystick fully.

Pilot pressure measured at the test port is below 3.5 MPa (500 psi).

Fix: Replace the pilot gear pump. This is a low-cost part compared to the main pump.

How to Diagnose the Problem in 3 Steps
Before buying any parts, run this quick on-site check:

Check hydraulic oil level and color. Low oil or milky (water-contaminated) oil causes weakness.

Measure pump pressure. Install a pressure gauge at the main pump outlet. Compare readings with the manual.

Observe warm-up behavior. If the machine works well cold but weakens hot, internal leakage is almost certain.

Preventive Maintenance to Avoid Slow Digging
Most slow-and-weak failures come from neglect. Follow these rules:

Change hydraulic oil and filter every 1,000 hours or once a year.

Use the correct viscosity oil (typically ISO VG 46 or 68 for mucking loaders).

Keep the tank breather clean – dust ingress kills pumps quickly.

Do not overspeed the engine when digging; high RPM without load accelerates pump wear.

When to Call a Specialist

If you have done the basic checks (oil level, filter, pressure test) and the mucking loader remains slow and weak, internal wear has progressed too far. Continuing to use the machine will damage other components, including cylinders and travel motors. Contact your dealer or a hydraulic repair shop before the next shift.