A site-preparation contractor reported that a Volvo EC220E crawler excavator had developed a progressive travel fault over a three-week period. When the operator commanded forward travel at full speed, the machine would drift noticeably to the left - requiring constant corrective steering input from the right-side travel lever to keep the machine tracking straight. The left-side travel also felt slightly weaker than the right during uphill travel with the boom raised. After roughly 20 minutes of continuous travel, the left-side travel motor's case was noticeably hotter than the right-side motor - hot enough that the operator could not rest a hand on the housing for more than a few seconds.
The technician first verified that the machine's track tension was correct on both sides and that both tracks showed even wear patterns - ruling out the simple causes that mimic a failed travel motor. He then connected the Volvo diagnostic tool and retrieved live data during a travel test cycle. The diagnostic tool showed the left travel motor's hydraulic supply pressure was 2 MPa lower than the right travel motor's pressure during high-demand travel, and the left travel motor's case-drain flow was noticeably higher than the right's - indicating excessive internal leakage past the left motor's internal components.
He understood the EC220E's travel architecture. Each track is driven by a dedicated "Travel Motor" - a hydraulic piston motor coupled to a planetary "Final Drive" gearbox whose output drives the sprocket. Hydraulic oil reaches the travel motors through the "Swing/Travel Rotary Manifold" - a rotary joint mounted at the machine's center that allows hydraulic oil to flow from the machine's upper structure to the travel motors while the upper structure slews. The rotary manifold contains seal rings that separate the individual hydraulic circuits passing through it. When a seal ring wears or fails, hydraulic oil can leak between adjacent circuits - producing cross-circuit leakage that can cause one travel motor to receive reduced flow while the other receives excess flow, producing the track pull the operator described.
He removed the swing/travel rotary manifold and disassembled it on a bench. The manifold's internal seal rings showed visible wear - the seal rings' outer surfaces had worn into oval profiles, and two of the rings showed visible cracking. The worn rings were allowing oil to leak between the left travel circuit and an adjacent low-pressure circuit - explaining the reduced supply pressure to the left travel motor and the asymmetric travel performance the operator described. He further inspected the left travel motor's "Case-Drain Line" - the line that returns the motor's internal leakage oil to the reservoir. The line showed a visible restriction at a kinked section where the hose had been bent during a previous repair, and the line's interior was partially clogged with degraded hydraulic oil residue. The restricted case-drain line had prevented the left motor's internal leakage oil from returning freely to the reservoir, elevating the motor's case pressure and compounding the motor's internal leakage - producing the overheating the operator described.
The root cause was traced to rotary manifold seal ring wear compounded by a restricted case-drain line. The manifold's seal rings had worn naturally over extended service (the machine had approximately 6,900 hours), and the worn rings had allowed cross-circuit leakage that produced the track pull. The kinked, partially clogged case-drain line had compounded the fault by elevating the left motor's case pressure, accelerating the motor's internal wear and producing the overheating.
The repair involved replacing the complete set of rotary manifold seal rings with new components, cleaning the rotary manifold's internal passages to remove any residual debris, and replacing the kinked case-drain hose with a new length of the correct specified hydraulic hose - routed to avoid the bend radius that had caused the original restriction. The hydraulic oil and return filter were replaced with fresh specified products, and the travel circuit was bled to remove trapped air. After reassembly, a loaded travel test showed the machine tracking straight with no drift, travel pressures balanced between the two sides, and the left travel motor's case temperature remaining within the normal operating range across a full 30-minute loaded travel cycle. Rotary manifold seal-ring inspection and case-drain hose condition checks were added to the machine's 1,000-hour preventive maintenance schedule.
