Track tension is one of the cheapest things to get right on an excavator and one of the most expensive to get wrong. Run the track too loose and it wears fast and can jump the sprocket. Run it too tight and every pin, bush, roller and idler carries a load it was never designed for. The part holding that balance is the track adjuster, and most operators never think about it until it fails.
Check track tension regularly and whenever ground conditions change. Tension is set by pumping grease into the track adjuster through its grease nipple, and released by carefully unscrewing the grease valve. A track that will not hold tension, or suddenly looks far too tight, usually means the adjuster itself has failed. We stock track adjusters for nearly 300 excavator models, ready for immediate delivery.
Why track tension matters
The track chain connects the drive from the final drive to the ground. For that to work, the chain has to sit correctly on the sprocket, the rollers and the idler. Correct adjustment is one of the basic habits that extends the life of the whole undercarriage, alongside keeping it clean and minimising time in reverse, because excavator chains are designed to wear less when travelling forwards.
A loose chain snakes and slaps as the machine travels. It is one of the recognised causes of a chain jumping on the sprocket, together with worn sprockets and worn track rollers, and on a rubber-tracked machine incorrect tension is a leading reason tracks come off altogether.
An over-tight chain is quieter but no kinder. It loads the pins, bushes, idler and rollers continuously, and gouged rail corners on the links are a known warning sign that tension needs adjusting. Mud and stone packed into the undercarriage has the same effect, tightening the track without anyone touching the adjuster, which is why cleaning out the frames is part of tension control.
What a track adjuster is and how it works
The track adjuster, also called a recoil spring assembly or track tensioner, is a mechanical part that fits in the undercarriage frame between a bulkhead and the idler. Its function is to keep the track correctly tensioned. Grease pressure in the cylinder pushes the idler forward, which takes up the slack in the chain and guides the links as they run.
| Component | What it does |
|---|---|
| Tensioning piston | A grease-filled ram. Pumping grease in extends it and tensions the track; draining grease releases it. |
| Spring pack | Absorbs impact as the machine travels, letting the idler recoil when the track hits an obstruction. |
| Yoke | A fork-shaped casting that bolts to the idler side arms and transfers the tension to the idler. |
The adjuster and the idler work as a pair. The adjuster pushes, the idler carries and guides the chain. That relationship matters again when it comes to replacement, as covered below. For a tour of every component around them, see our guide to excavator undercarriage parts.
How to check and adjust track tension
Checking
Park on firm, level ground and clean any packed mud and stone out of the undercarriage first, because packing gives a false reading. Measure the sag in the track against the figure in your operator's manual. The correct figure varies by machine and by track type, so the manual is the reference, and softer ground generally calls for a slightly slacker setting than hard standing. If you would rather have it measured properly, our free track inspection service records wear across every undercarriage component, including chain stretch, and reports what needs attention.
Tensioning
Tension is set by pumping grease through the grease nipple on the adjuster with a grease gun. The grease extends the piston, the piston pushes the idler forward and the slack comes out of the chain. Add grease gradually, travel the machine back and forth, and measure again rather than guessing.
Releasing
Tension is released by unscrewing the grease valve. The grease in the cylinder is under pressure, so unscrew the valve carefully and let the grease drain until the pressure is fully relieved. Never remove the valve before that pressure is gone. If you are not confident doing this, leave it to a trained fitter. Our onsite fitting teams handle track and undercarriage work daily.
The four ways a track adjuster fails
- The yoke cracks. The cast yoke can crack when the undercarriage takes excessive impact.
- The rod breaks. The rod holding the spring can break, causing over-tension. The giveaway is a track that suddenly looks far too tight.
- The spring cracks. A cracked spring often goes unnoticed until the idler is changed and the assembly is stripped.
- The piston seals fail. Failed seals let the grease escape, so the track will not hold tension no matter how often it is pumped up.
If your machine shows any of these symptoms, stop pumping grease at the problem and get the assembly inspected. A failed adjuster passes shock and slack straight into the chain, rollers and sprockets and shortens the life of all of them.
Replacing a track adjuster
Track adjusters are replaced as complete assemblies. The most important rule is to look at the idler at the same time, because a worn idler can cause a new track adjuster to fail prematurely. That is also why the two warranty terms differ, and why the most economical time to fit a new adjuster is when the idlers are being replaced anyway.
Astrak track adjusters are available from stock for immediate delivery for nearly 300 excavator models, including Case, CAT, Daewoo, Doosan, Hitachi, Hyundai, JCB, Kobelco, Komatsu, New Holland, Takeuchi and Volvo machines.
Every DuraTrack track adjuster assembly is inspected thoroughly throughout the manufacturing process to ensure proper fitment and performance. Warranty: 12 months when purchased and fitted along with a new idler, 6 months when fitted without one. Order by 4:30pm for next working day UK delivery.
Browse the track adjuster range, matching idlers, or the full undercarriage range. If you are unsure which assembly fits your machine, send us the make, model and serial number and we will confirm it.
Frequently asked questions
How do I check track tension on an excavator?
Park on firm, level ground, clean packed mud and stone out of the undercarriage, then measure the sag in the track against the figure in your operator's manual. The correct figure varies by machine and track type. Astrak also offers a free track inspection service that measures wear across every undercarriage component, including chain stretch.
How do you adjust track tension on an excavator?
Tension is set by pumping grease through the grease nipple on the track adjuster with a grease gun. The grease extends the tensioning piston, which pushes the idler forward and takes the slack out of the chain. Add grease gradually and re-measure rather than guessing.
How do you release track tension on an excavator?
Tension is released by unscrewing the grease valve on the track adjuster. The grease is under pressure, so unscrew the valve carefully and let the grease drain until the pressure is fully relieved before the valve is removed. If in doubt, leave it to a trained fitter.
What is a track adjuster?
A track adjuster, also called a recoil spring assembly or track tensioner, is a mechanical part that fits in the undercarriage frame between a bulkhead and the idler. Its job is to keep the track correctly tensioned. It has three integral parts: a grease-filled tensioning piston, a spring pack that absorbs impact, and a yoke that bolts to the idler.
Why does my excavator track suddenly look too tight?
A track that looks far too tight is a classic sign that the rod holding the spring inside the track adjuster has broken, causing over-tension. Do not keep working the machine on it. Get the assembly inspected and replaced.
How long is the warranty on an Astrak track adjuster?
12 months if purchased and fitted along with a new idler, or 6 months if fitted without a new idler. The reason is that a worn idler could cause a new track adjuster to fail prematurely.
Get a quote for your track adjuster
Send us the machine make, model and serial number and we will confirm the correct track adjuster assembly, whether your idlers are due at the same time, and current availability.
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.
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