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Kubota 121-3 Replacement Tension Idler

Kubota 121-3 Idler RD118-21300
Kubota 121-3 Replacement Tension Idler
Buy aftermarket front idlers for your Kubota 121-3 mini excavators online at Rubbertrax to save time and money. Save online and skip the trip to the dealer. This idler ships for free when you check out online.
SKU: RD118-21300
Weight: 77 lbs
Make: Kubota
Shipping: Fast and Free!
Price: $518.00

Rubber tracks and wear parts are sold individually unless specified in the details. We offer free shipping across the USA when you order online and ship to a commercial address. *Some restrictions apply.

RD118-21300 Tension Idler Assembly

This is the aftermarket replacement front tension idler for the following Kubota mini excavators:

  • Kubota KX 121-3
  • Kubota KX 121-3SS
  • Kubota KX 121-3ST 
  • Kubota KX 040-4

This idler is a complete assembly with mounting brackets.

The idler must be replaced when significant wear is present to keep the track tensioned properly. If you run on worn idlers the track will lose tension and many other problems will occur such as de-tracking. Keep your track tensioned properly by greasing the tension idler into place and check the tension daily and evaluate the wear on the sprockets and idlers. Uneven wear will result in premature track damage. You will see the best results and longest lifespan of the undercarriage if you maintain the tension and replace worn parts at the same time.


This part is commonly referred to as a tension wheel or tension pulley, but it does not come with the actual spring tensioner. The idler comes fully assembled as seen in the picture.

Alternate Part Numbers

  • Kubota Dealer Part Number: RD118-21300, RD148-21300, RD158-21302

Alternate Models

This idler assembly (RD118-21300) is known to fit:

  • Kubota KX 121-3
  • Kubota KX 121-3SS
  • Kubota KX 121-3ST
  • Kubota KX 040-4

Quality Kubota Parts

These single flange idler assemblies are made to original specifications and produced with high quality seals to lock dirt and debris out and lock the lubrication in for long lasting service for your machine. We guarantee fit.

Kubota KX 121-3 Undercarriage Parts

Here is the complete line of undercarriage parts for the Kubota KX 121-3 including the rubber track, drive sprocket, bottom rollers, top rollers, and tension idler.

Kubota 121-3 Sprocket RD118-14433 Kubota Top Carrier Roller RD411-22900Kubota Bottom Roller RD118-21700 Kubota Tension Idler RD118-21300