Hitachi EX300-5–EX370HD-5: rock equipment, modes and drift

EX350 reinforcement and EX370 running gear

The EX350H and EX350LCH front assemblies have thicker plates than the EX300 attachment. Arm-bottom protection, reinforced linkage and bucket wear plates address rock contact; these are physical differences to inspect, beyond the extra operating weight. Their heavier counterweight supports that front equipment.

An EX300 wearing a rock bucket does not thereby acquire the H-series structure.

The EX370HD goes further: Hitachi describes an EX400-class undercarriage, reinforced track guards and a pressurized cab with an integrated headguard. Front cab guards and a full track guard were optional. Check which guards remain on a used machine.

High-power operation is conditional. The brochure's DIN schedule raises output from 169 to 177 kW when heavy work demands it, then returns to standard output during light swing or dumping. Economy mode reduces engine speed.

Grading mode deliberately slows arm-in and quickens arm-out, while attachment mode matches oil delivery to the tool. Slow arm-in during grading therefore needs a mode check before it is treated as evidence of a worn pump.

Separate an initial boom dip from continuing drift

Hitachi's troubleshooting drawing distinguishes low-flow behavior at the start of an operation from continuing cylinder leakage. With a malfunctioning load-check valve, oil from the boom cylinder's bottom chamber can return into the circuit before pump delivery builds. The boom may retract briefly.

That sequence matters: a dip as another function begins is a different observation from a boom that continues descending after the controls return to neutral.

The same manual note describes excessive piston-to-barrel clearance. At low initial pump flow, leakage through that clearance can also cause temporary retraction; continuing drift increases as the gap grows. A visible external hose leak is therefore not the only possible explanation.

Record whether the movement is momentary or sustained and which control operation precedes it; the illustrated alternatives need hydraulic diagnosis, not an assumed cylinder replacement.

A separate travel flowchart checks the travel-pressure signal and its wiring, a solenoid circuit, and travel-motor swash-angle response before reaching a motor or reduction-gear conclusion. Machine-controller feedback and the measured pressure are compared together. A travel complaint alone does not identify a failed final drive.

Support the attachment and follow the complete manual's isolation procedure before any pressure testing.