Vermeer LM42 Trencher: Maintenance, Troubleshooting, and Practical Insights

[MikePhua]

Overview of the Vermeer LM42 Trencher
The Vermeer LM42 is a compact, ride-on vibratory plow and trencher combination designed for utility installation, particularly in tight residential or light commercial environments. With a chain trencher attachment and an option for a plow blade, it serves applications like fiber optic cable installation, irrigation lines, and light electrical conduit burial.
Its durable construction and reliable hydrostatic drive have made it popular among contractors. However, like any mechanical system, especially one with hydraulic and mechanical drivetrain integration, the LM42 requires careful maintenance and occasional troubleshooting.
Basic Specifications and System Layout
The Vermeer LM42 features:

• Engine: Typically equipped with a Deutz or Kohler diesel engine, delivering 42–50 HP, air-cooled
  
• Drive: Dual hydrostatic ground drive motors powering rear wheels independently
  
• Trencher Boom: Capable of depths up to 42 inches with various chain configurations
  
• Hydraulics: Dedicated pumps for drive, trencher chain, and optional backfill blade or plow
  
• Controls: Lever-operated mechanical controls or pilot valves depending on model year
  

The machine's simple footprint makes it ideal for one-person operation, but understanding the intricacies of its drivetrain and hydraulic routing is essential for keeping it productive.
Common Maintenance Areas
The LM42, like other trenchers, sees most of its wear in the drive chain, boom bearings, and hydraulic system. Regular maintenance not only reduces breakdowns but also preserves resale value.
Key maintenance items include:

• Trencher Chain
  • Daily inspection for wear and slack
    
  • Lubricate or replace worn pivot links
    
  • Check teeth sharpness and replace missing or chipped ones
    
  • Inspect drive sprocket for rounding or uneven wear
    
• Boom Bearings
  • Grease regularly using high-load lithium-based grease
    
  • Inspect for play or wobble in the trencher boom assembly
    
  • Replace seals if grease leaks out or water intrusion is suspected
    
• Hydraulic System
  • Change hydraulic filters every 250 hours or as specified
    
  • Inspect hoses for rub-throughs and fittings for seepage
    
  • Use only recommended hydraulic oil; avoid mixing types
    
  • Check pressure relief valves if functions become sluggish
    
• Wheel Motors and Hubs
  • Check for leaking seals around drive motors
    
  • Monitor for weak pulling or loss of power on slopes, a sign of internal bypass
    
  • Inspect wheel bearings and lubricate as required
    

One user noted that regular replacement of the chain tensioner spring prevented damage to the boom housing—an inexpensive part that prevents expensive downtime when left ignored.
Hydrostatic Drive and Troubleshooting Power Loss
The hydrostatic drive is often misunderstood but is critical for maneuvering the LM42, especially on inclines or in wet soil. The system uses variable-displacement pumps feeding fluid directly into wheel motors, with power proportionate to flow and pressure.
If the machine becomes sluggish, common causes include:

• Weak charge pump: This small pump primes the main system. Low pressure here means cavitation and weak movement.
  
• Worn wheel motors: Internal wear causes pressure to bypass internally—results in weak pulling or unresponsive turning.
  
• Contaminated hydraulic fluid: Debris in the fluid wears down pump and motor components, reducing efficiency.
  
• Loose control linkages: Mechanical linkage from operator controls to hydro pump may become worn or loose, reducing stroke range.
  

A common diagnostic method is to measure case drain flow from each wheel motor. Excess flow indicates internal leakage—usually requiring motor replacement.
Starting Issues and Electrical Considerations
Some LM42 models have quirky electrical systems, especially in early 2000s units with minimal shielding or protection against moisture ingress.
Symptoms of electrical problems include:

• Starter motor not engaging
  
• Glow plug system failing to activate (on diesel models)
  
• Safety switches disabling engine crank unexpectedly
  

To troubleshoot:

• Inspect seat safety switch and parking brake switch, as both must be satisfied for engine start
  
• Check starter solenoid and ignition switch continuity using a voltmeter
  
• Verify battery voltage and connections; look for corrosion at terminals
  
• Inspect fuse block and relays under dash for signs of water damage
  

An operator once traced a no-crank issue to a broken ground wire hidden under the engine pan, corroded after years of exposure to road salt during winter trenching jobs.
Replacing Drive Chains and Understanding Wear Patterns
Trencher chains are sacrificial components—meant to be replaced periodically. Uneven soil types, rock content, and operator technique all affect wear rate.
Signs of a worn chain include:

• Skipping or “bucking” when under load
  
• Poor trench profile—too wide or uneven depth
  
• Shiny contact points and slack between links
  
• Chain slap when boom is retracted
  

When replacing the chain:

• Use OEM or high-quality aftermarket links matched to soil conditions (cup teeth for soft, shark/rock teeth for mixed)
  
• Inspect drive sprocket and tail roller for pitting or deformation
  
• Tighten chain to manufacturer-specified slack when cold, as heat expands metal
  

A seasoned utility crew in Arizona reported that switching from generic chains to tungsten-carbide-tipped teeth extended chain life by nearly 40%, especially in caliche-laden soil.
Operational Tips and Field Efficiency

• Set chain speed based on soil—faster isn’t always better. In clay or wet ground, slower RPMs allow for cleaner cuts.
  
• Use down pressure strategically—excess force stalls the chain or overtaxes hydraulics. Let the chain “chew.”
  
• Clear spoil regularly—clogged augers or backfill plates reduce efficiency and may cause overheating.
  
• Adjust boom angle for grade—level boom for shallow lines; pitch down slightly for deeper trenches.
  

In one documented case, an operator digging fiber lines on a suburban project found that trenching in 12” increments with passes between trees reduced lateral root damage and minimized machine stress.
Conclusion: The LM42 as a Reliable Mid-Sized Workhorse
The Vermeer LM42 has earned its reputation as a dependable, efficient tool for small- to mid-scale trenching and utility work. Its straightforward design, when maintained properly, provides years of service.
However, ignoring basic hydraulic maintenance, trenching technique, or wear component monitoring can lead to cascading failures. In environments with varying soil and climate conditions, proactive maintenance isn’t just smart—it’s essential.
As one field tech noted after restoring a heavily used LM42: “It’s a simple machine, but it talks to you. If something feels off—chain skips, steering fades, a strange rattle—it’s telling you what’s wrong. You just have to listen.”