Track derailment, commonly known as “throwing a track” or “breaking the chain,” is a frequent headache for excavator operators working in harsh environments. Whether it’s mud, stones, or general wear and tear, a derailed track brings productivity to a halt. In this post, we’ll explore the primary causes of track derailment in crawler excavators and share practical solutions—including how to reinstall a track efficiently.
Track derailment happens when the track slips out of the guiding path formed by the idler, carrier roller, track roller, and sprocket—collectively known as the “four wheels and one track.” While operator technique plays a role, repeated derailment often points to underlying mechanical issues.
Here are the three most common causes:
-
1. Misalignment of the “Four Wheels and One Track”
If the idler, sprocket, carrier rollers, and track rollers are not aligned on the same plane, the track is prone to slipping off. This typically indicates wear or damage to the idler or other components. In such cases, replacing the idler—or other worn parts—is necessary to restore proper alignment.
-
2. Excessive Track Slack
Track tension is controlled by the tensioning cylinder, which is adjusted by injecting grease with a grease gun. When the track is too loose, derailment becomes likely.
However, if the track cannot be tightened even after adding grease, the problem may be worn-out pin and bushing assemblies on the chain rails. Once the pin bushings are worn through, simply adjusting tension won’t help. While some shops offer “pin pressing” services to replace individual bushings, many today opt to replace the entire chain rail assembly for reliability and longevity.
-
3. Worn-Out Track Guard (Carrier Guard)
Unlike bulldozers, which feature full-length track guards running from the sprocket to the idler, most excavators only have small guard plates—usually located near the center track roller and the idler. Once these guards wear down, the track rail can easily slip off the rollers, leading to derailment.
If the guard is bent, cracked, or heavily worn, repairing or replacing it is the only effective fix.
There’s no universal method for reinstalling a thrown track, but the general approach remains consistent: relieve track tension and carefully maneuver the track back into place using the excavator’s bucket and travel functions.
-
Step 1: Release Track Tension
Start by loosening the grease valve on the tensioning cylinder to fully release track tension. This creates the slack needed to guide the track back onto the rollers.
-
Step 2: Position the Track
If the track has slipped outward, the bucket can often be used to push or lift it back toward the rollers. If the track has slipped inward (toward the machine center), the bucket may not reach. In that case, use a wire rope or sling to pull a section of the track onto the idler or sprocket before engaging the travel motor.
-
Step 3: Seat the Track on the Sprocket and Idler
Once the track is aligned with both the drive sprocket and idler wheel, the hardest part is complete. The remaining sections—especially around the track rollers—can often be set by lifting the track with the bucket and rotating it slowly.
-
Step 4: Handle the Carrier Roller Section
If the bucket can’t reach the carrier roller area, a simple trick can help: lift the track with the bucket, place a sturdy wooden beam under the track near the carrier roller, and slowly lower the track. The beam will push the track upward, guiding it into place over the carrier roller.
Track derailment is more than an inconvenience—it’s a sign that something in your undercarriage needs attention. Whether it’s misaligned components, worn chain rails, or damaged track guards, early diagnosis can save hours of downtime and costly repairs.
Keeping your undercarriage in good working order—and knowing how to handle a thrown track when it happens—will keep your excavator productive, even in the toughest conditions.
Need reliable undercarriage parts? Contact us today for high-quality track components designed to withstand the toughest jobsites.
