Track Idler Worn or Leaking? Rebuild, Replace and Match It Right

Front idler weeping oil, wobbling or knocking once a turn? A leak left too long usually damages the inside. Check for leaks and play, measure the wear, then decide whether it stays, and match any replacement to the exact machine.

PartsForMachines lists over 1,000 track idlers and idler assemblies, front and rear, for mini diggers, excavators, dozers and compact track loaders.

How Do I Know My Track Idler Is Worn Out?

Look for oil around the hub, play as it turns and a worn running surface, then measure it to be sure. Oil at the seals means a seal has failed. Watch the idler as the track runs slowly: any wobble or slack points to worn bushes.

Wear on the surface the chain runs on is hard to judge by eye, so measure it and compare the figure with the wear limit for your machine. If it knocks at the same point every turn, make these checks straight away.

Idler Leaking Oil: Can I Top It Up, or Is It Finished?

Topping up won’t cure it, and an idler that has leaked for long is usually damaged inside and due for replacement. Track idlers are normally sealed and filled with oil for life, so a leak means a seal has failed and the oil will keep escaping.

As the oil runs low, friction heats the inside and the damage builds. Check the hub and seal area at every service to catch a weep early. If it has already lost much of its oil, a complete replacement, such as the ID42690 idler assembly for the Terex TC29, is usually the sounder fix.

Can a Mini Digger Idler Be Rebuilt, or Must I Replace It?

On a mini digger or compact track loader, replacement is the usual answer once the idler is worn past its limit or damaged inside. These small idlers are sealed for life, so a new assembly is usually the practical fix.

Most of our range is listed as idler assemblies, such as the ID26392 idler assembly for the JCB 8032. Before you write off the old one, measure it: if it is within its wear limit, dry and free of play, it can stay in service.

Will a New Idler Fit? How Do I Match It to My Machine?

Match it by the exact machine and version first, then by the end and mounting it fits. One model can take different idlers by serial number, track or arm. The ID32874 idler assembly, for example, is listed only for the Komatsu PC20R-8 with serial numbers starting F. Several JCB JS excavators are listed with both a standard idler and a 240mm side-arm version.

Have an original part number from the old idler or parts book? Search our site for it: over 150 of our idlers are listed by the OEM number they replace.

What Should I Check Before I Order?

• the make, model and full version from the machine plate, including suffixes such as LGP or XL (the Caterpillar D5M has a separate idler for each)
• the track it runs: some models take a different idler by chain pitch, such as the 135-pitch and 154-pitch versions for the Caterpillar 307B
• which end and mounting: front or rear on a compact track loader, standard or side-arm on some excavators
• any part number on the old idler or in the parts book
• the part type you are taking off: most of the range is idler assemblies, but some are listed as front idlers, rear idlers or simply idlers

Browse the Idler range, or contact the PartsForMachines team by WhatsApp, telephone or email with the machine model, serial plate and photos of the old idler.

Product options, delivery options and returns terms are shown on each product page. A 30-day return policy applies to eligible items.

Frequently Asked Questions

Does a track idler need oil changes or greasing?

Normally neither. Most idlers are sealed and lubricated for life, so they need no routine oil changes. If yours has a fill or level plug, follow the machine’s manual for the lubricant.

Is there a bearing inside a track idler?

It can have bushes, bearings or both, sealed in with the oil. Either way, slack or wobble in the wheel means they are wearing, so rock the idler and check it whenever the track is off.

What does a track idler actually do?

The front idler guides the track chain round the end of the frame, and its flanges help keep the track in line and on the undercarriage. The track adjuster pushes it away from the sprocket to keep the track tight.

Can I check idler wear without taking the track off?

Usually, yes. Use a depth gauge to measure from the top of the idler down to the surface the chain’s rails ride on, then compare the figure with the wear limit or percent-worn chart for your undercarriage.

Can a track idler crack?

It can: a loose track working in harsh ground has been known to fracture one. Look over the rim and the centre for cracks whenever you inspect the undercarriage, and if you find one, get advice on repair or replacement.

Front or rear idler: which does my track loader need?

Many compact track loaders take a different idler at each end, listed as front and rear, as on the Case TR270. Order the end you’re replacing, by machine or original number: the ID10812 front idler, for example, replaces Caterpillar 304-1878.

Will a used idler do for an older dozer?

It can, as long as it is inside its wear limit, dry at the seals and tight on its bushes. Match the exact version too: dozer idlers are often listed separately for LGP and XL machines, as with the D5M.

How do I get the front idler out of a mini digger?

Follow your model’s workshop manual, as the steps vary. In outline, slacken the track at the adjuster and lift it clear of the idler. Note how the idler sits in the frame before drawing it out, so the new one goes back the same way.