Why Do Digger Tracks Come Off? Causes, Fixes And Prevention

A thrown track stops the machine where it stands. Getting it refitted is the immediate job. Finding out why it came off is what stops it happening again, and this guide covers the documented causes and the checks that identify them.

Tension: the first thing to check

The track adjuster fits in the undercarriage frame between a bulkhead and the idler, and its function is to keep the track correctly tensioned. It has three integral parts: a tensioning piston, which is a grease-filled ram, a spring pack that absorbs impact, and a fork-shaped yoke that bolts to the idler side-arms or blocks. Tension is set by pumping grease in through a nipple and released by carefully unscrewing the grease valve.

Four failure modes matter here, and two of them directly loosen the track:

• Piston seals fail, so the adjuster no longer holds grease pressure and tension is lost. A slack track can come off.
• The spring cracks, which often goes unnoticed until the idler is changed.
• The rod holding the spring breaks, and the track suddenly looks far too tight. Over-tension is also a fault.
• The cast yoke cracks under excessive impact.

Our guide to track adjusters covers the range, and remember the pairing rule: adjusters carry 12 months' warranty fitted with a new idler, 6 months without.

Worn parts that throw tracks

A chain that jumps on its sprockets is close to coming off. The documented causes are specific: worn sprockets, a broken track adjuster spring, offset sprockets fitted the wrong way round, the wrong pitch, or worn track rollers. Track guards help keep the chain in line while the worn component is identified and replaced.

There is a second cost to ignoring it. Sharp and worn sprockets can result in the link slipping or jumping through the sprockets, and that shock loading damages the final drive motor. A worn sprocket costs far less to replace than the final drive it damages.

Wear on sprockets, rollers and idlers is measured as a percentage against new dimensions in a track inspection, which is the reliable way to find the component responsible.

Habits and ground conditions

Some contributors are operational rather than mechanical, because anything that accelerates or concentrates wear brings the mechanical causes forward:

• A packed undercarriage. Material packed between rollers, links and sprocket teeth stops the components engaging correctly and accelerates wear. Regular cleaning helps, as do centre punched shoes, and roller guards should only be used when necessary.
• Always turning the same direction, an operating habit that wears the undercarriage unevenly.
• Terrain loading. Side hill working loads the downhill side components, crown running loads the inboard components and depressions load the outboard components, so wear concentrates on those components.

Rubber tracks and anti-detracking design

On rubber-tracked machines the same fundamentals apply, tension, guidance and wear, but track construction matters too. TerraTrack Plus is built from toughened steel links joined by continuously wound anti-rust high tensile steel cords, encased in an advanced abrasion-resistant rubber carcass. Its interlocking link design is engineered specifically for anti-detracking performance, and every TerraTrack Plus and TerraTrack rubber track carries a full 24-month warranty.

Fitting the correct size matters as much as the track itself. Pitch differences between otherwise similar tracks are covered in our guide to long pitch and short pitch rubber tracks.

Getting the track back on

Refitting a thrown track is a job for a fitter with the right equipment. Utilising a nationwide network of approved plant fitters, our fitters will come to you anywhere within the UK through our onsite fitting service. Once the machine is moving again, book a free track inspection so the component that threw the track is found and replaced before it happens again.

Frequently asked questions

Why do digger tracks come off?

Because tension, guidance or component wear is wrong, and often more than one at once. Common causes are a failed track adjuster losing tension, worn sprockets or track rollers, offset sprockets fitted the wrong way round, the wrong pitch, a packed undercarriage and side hill working.

Why do the tracks keep coming off my mini digger?

Repeated detracking almost always has an underlying cause: lost tension from a failed adjuster, worn sprockets letting the track slip and jump, worn rollers or the wrong track fitted. A track inspection measures each component against new dimensions and identifies which one is responsible.

What should I do when a track comes off?

Stop the machine and get a fitter to refit it with the right equipment. Our nationwide network of approved plant fitters comes to you anywhere within the UK. Then find the cause: if nothing changes, the track will come off again.

Can a track be too tight?

Yes. A broken rod in the track adjuster spring pack makes the track look far too tight, so over-tension is a failure symptom, not a safety margin. Tension is set by pumping grease in through the nipple and released by carefully unscrewing the grease valve.

Do worn sprockets damage anything else?

Yes. Sharp and worn sprockets can let the link slip or jump through the sprockets, and that shock loading damages the final drive motor. Replacing a worn sprocket costs far less than replacing the drive behind it.

Astrak Group develops and manufactures products intended to be compatible with machinery and equipment from various manufacturers. Unless indicated otherwise, Astrak Group has no relationship, commercial or otherwise, with the owners of the trademarks.