312 CL Track Adjuster Failure

[MikePhua]

A Caterpillar 312 CL excavator presenting a stuck track adjuster that stubbornly refuses grease provides an excellent case study in diagnosing and resolving this common undercarriage issue. This account walks through background, mechanical anatomy, problem-solving tips, and safety considerations—all in a fresh narrative style.
Excavator Background
The Caterpillar 312 CL, introduced in the late 1990s, is a mid-size tracked excavator celebrated for balancing productivity and maneuverability. It sports a robust Cat C4.4 diesel engine delivering around 93 hp, paired with a durable undercarriage engineered for daily excavation, grading, and trenching duties. Over its production run, Cat built tens of thousands of these machines globally—widely adopted across construction and utility sectors for their reliability and parts commonality.
Track Adjuster Anatomy
The track adjuster is a grease-filled cylinder with an internal spring or hydraulic mechanism that maintains track tension. Key parts include:

• Piston rod – extends outward to tension the track.
  
• Grease valve/zerk – injection port for lubrication.
  
• Pressure relief bolt – used to bleed excess grease or relieve pressure.
  
• Seals – retain grease and block contaminants.
  

These components ensure proper tension, reduce track wear, and prevent derailing.
Symptom and Diagnosis
In the scenario, attempts to inject grease cause the grease coupler to pop off after just a few pumps. Even with a new fitting and cordless grease gun set to high pressure, lubricant fails to enter the adjuster, indicating an internal seizure—not a faulty fitting.
Pushing the idler inward slightly only loosened the track further, but didn't enable grease uptake. Expert consensus suggests that when grease won't go in, the adjuster is mechanically seized—either corroded inside or blocked by debris. The spring-mechanism may have collapsed, seals failed, or rod corrosion prevented movement.
Steps Toward a Solution

• Remove the grease nipple completely and attempt to push the idler fully inward—using either the dipper arm or a block to rotate the track. This physical movement can free the adjuster enough to accept grease.
  
• Loosen the pressure relief valve—a 5/8-inch bolt beneath the grease zerk—to vent trapped grease and release tension.
  
• If grease still won’t enter, the assembly may need removal. The official procedure for the serial range involves splitting the track, sliding out the front idler along with the recoil mechanism, and pulling the adjuster out. In some cases, removing a track roller allows adjuster removal through an access hole in the carriage without track splitting.
  
• In field fixes, some operators resort to powering grease through with a high-pressure manual grease gun. They may even use an air-over-hydraulic jack or heat the area to break rust.
  

Terminology Explained

• Seized adjuster: Internal rust or debris causes failure to move, preventing grease intake.
  
• Zerk (grease nipple): Injection point for lubrication; can clog or spin in place.
  
• Pressure relief valve: Allows controlled release of grease pressure; assists in adjustment.
  
• Track sag: Excess slack between idler and carrier rollers; over-tight or loose tracks accelerate wear.
  

Maintenance and Preventive Tips

• Use a quality lever-type grease gun—the higher pressure can often work better than battery-powered units.
  
• Replace grease nipples whenever clogged or spinning. They’re inexpensive and simple to swap.
  
• Adjust track tension periodically and monitor for proper sag—typically measured from track frame to bottom grouser pad. Too tight or loose accelerates wear.
  
• Keep the adjuster protected from moisture and corrosion by regular cleaning of the area and re-greasing before storage or periods of inactivity.
  

A Field Anecdote
One machine owner reached a point where the grease coupler popped off every time he pumped—without insertion. After freeing the seized adjuster with a pry and then easing it back with grease pressure, track tension slowly returned. He joked that the machine “just needed a stern talk with the bucket.”
Safety Considerations
Track adjusters often face high internal pressure and potent springs. Always safely release pressure before disassembly to avoid injury. Lock out the machine, relieve residual pressure via the relief port, and wear PPE before working near moving parts or splitting tracks.

Summary
Track adjuster failure on a Cat 312 CL typically stems from internal seizure. Start simple—remove the nipple, loosen relief valve, free the idler, and attempt re-greasing. If that fails, follow removal procedures or consult for replacement. Preventative maintenance—cleanliness, fit-and-replace nipples, and correct tension checks—yields long undercarriage life. Let me know if you’d like to expand with a maintenance schedule or track-tension reference guide!