Komatsu D155 Vibration Problems: Complete Diagnosis and Repair Guide

Vibration on a D155 Is Never Normal — Here Is How to Find the Cause

The Komatsu D155AX-5 (and all D155 series dozers) weighs approximately 39 tonnes and is powered by a SAA6D140E-5 engine producing 354 HP. At this scale, any vibration that is perceptible to the operator represents a significant amount of mechanical energy being transmitted through the machine's structure. Dismissing vibration as "normal for a big dozer" is a costly mistake — it always indicates a component that is either worn, misaligned, or operating outside its design parameters.

This guide systematically covers the six most common causes of abnormal vibration on D155-series dozers, ranked from most to least likely. For each cause, we explain the diagnostic method, the expected findings, and the corrective action.

Cause 1: Worn Engine Mount Cushion Dampers (Most Common)

The 8A31-54-1130 and 8A31-54-1140 rubber cushion dampers are the primary vibration isolation elements between the D155's engine and the main frame. These are the first components to inspect when vibration symptoms appear, because they degrade gradually and are the most common root cause of operator-perceptible vibration on D155 machines over 4,000 hours.

Diagnostic Method:

• Visually inspect all accessible cushion damper surfaces for cracking, chunking, oil contamination, or compression set
• Measure the free height of each cushion and compare to the original dimension (consult Komatsu shop manual Section 13)
• With the engine running at idle, observe the engine for excessive movement relative to the frame
• Check for shiny contact marks on frame surfaces near the engine — evidence of engine-to-frame contact during operation

Corrective Action: Replace the 8A31-54-1130 primary mount and 8A31-54-1140 secondary mount simultaneously. Never replace only one mount — uneven isolation causes worse vibration than uniformly worn mounts.

Cause 2: Cab Mount Deterioration

The D155AX-5 operator cab is mounted on its own set of rubber isolation mounts, separate from the engine mounts. Even if the engine mounts are in good condition, worn cab mounts can amplify the vibration experienced by the operator.

Diagnostic Method: With the engine off, push firmly on one corner of the cab and release. The cab should return smoothly to its resting position without bouncing. If the cab bounces more than once or does not return to center, the cab mounts are worn. Also inspect visually for rubber cracking and compression set.

Corrective Action: Replace all cab mounts as a set. This is a separate operation from engine mount replacement and addresses a different vibration path.

Cause 3: Track Tension Imbalance

Incorrect or uneven track tension is a frequently overlooked cause of vibration on crawler dozers. Tracks that are too tight create excessive load on the final drives and idlers, while tracks that are too loose slap against the track frame during operation. Uneven tension between left and right tracks causes the machine to vibrate asymmetrically.

Diagnostic Method: Measure track sag at the midpoint between the carrier rollers per Komatsu's specification (typically 30-50 mm for the D155, but verify against your shop manual). Compare left and right sides — they should be within 5 mm of each other.

Corrective Action: Adjust track tension using the grease-filled tensioner cylinder to bring both tracks within specification. If the tracks cannot be tensioned properly, check for worn links, bushings, or a leaking tensioner.

Cause 4: Hydraulic Pump Cavitation or Worn Bearings

The D155's hydraulic pumps can produce vibration symptoms that mimic engine mount failure. Pump cavitation (caused by restricted suction lines, low hydraulic oil level, or aerated oil) creates high-frequency vibration and an audible whine. Worn pump bearings create lower-frequency vibration that increases with engine speed.

Diagnostic Method: Isolate the source by running the engine at idle with the hydraulic system in neutral (no implement load). If vibration is present at idle, the source is the engine or mounts. If vibration only appears when hydraulic functions are activated, the source is the hydraulic system.

Cause 5: Engine Internal Imbalance

In rare cases, internal engine issues — worn crankshaft vibration damper (harmonic balancer), misfiring cylinders, or injector problems — can cause vibration that is transmitted through even good engine mounts. These causes are less common than mount degradation but should be investigated if mount replacement does not resolve the vibration.

Diagnostic Method: Check for diagnostic trouble codes on the Komatsu EMMS (Engine Monitor and Management System). Run an engine cylinder cutout test to identify misfiring cylinders. Inspect the crankshaft vibration damper for rubber separation or wobble.

Cause 6: Fan Drive or Belt Misalignment

A worn or unbalanced cooling fan, a misaligned fan drive pulley, or a deteriorated drive belt can create localized vibration that the operator may perceive as a whole-machine issue. This vibration typically has a higher frequency than engine mount-related vibration and may change pitch with engine RPM.

Diagnostic Method: Visually inspect the fan blades for damage, cracks, or missing balance weights. Check belt condition and tension. With the engine off, spin the fan by hand and check for bearing roughness in the fan drive assembly.

Order D155 Replacement Cushion Dampers

If your D155 vibration diagnosis points to worn engine mounts, we supply the complete range of replacement cushion dampers:

All parts are ISO 9001:2015 certified and in stock for immediate worldwide shipment. Contact us with your machine serial number for verified fitment confirmation.

Frequently Asked Questions