CAT 303.5 Rubber Tracks: Which Track Fits Your Model, Wear Signs And Replacement

The rubber tracks on a CAT 303.5 mini excavator carry the whole machine, and the 303.5 has been built in several generations that do not all take the same track. This guide covers how to identify the right replacement track for your 303.5, the wear and detracking signs to watch for, and what to check on the rest of the undercarriage before the new tracks go on.

What the rubber tracks do on a CAT 303.5

A mini excavator runs on a continuous rubber track on each side of the machine. Each track runs around a drive sprocket, which is bolted to the final drive, over the front idler and along the bottom rollers in the track frame. The sprocket teeth engage the metal links moulded inside the track, so the track pitch has to match the sprocket pitch exactly for the drive to work without skipping.

A TerraTrack rubber track is built from toughened steel links joined by continuous high tensile steel cords, encased in a heavy duty rubber carcass with a premium grade rubber compound and a unique tread design. The cords carry the load, the links take the drive from the sprocket and the rubber grips the ground.

Identifying the right track: which 303.5 do you have?

The 303.5 model name covers more than one machine. In our catalogue the 303.5 CR, 303.5C CR, 303.5D, 303.5D CR, 303.5E, 303.5E CR and 303.5E2 CR each have their own rubber track listing, and the Next Gen 303.5 CR with a CE9 or RE9 serial number prefix is listed separately again. The 303.5 CR and the 303.5E are listed against different TerraTrack part references, so the generation and the serial number prefix come first.

The second thing is the size on the track itself, written as width x pitch x links, so 300 x 52.5 x 80 means a 300mm wide track with a 52.5mm pitch and 80 links. Width alone never identifies a track, because tracks of the same width are made in several pitches. The full size, including any letter suffix, is the final check.

1. Note the exact model and the serial number prefix from the machine plate.
2. Read the size moulded into the inside face of the existing track.
3. If it is not legible, measure the pitch centre to centre between two adjacent metal links, in millimetres. It is not the gap between the links.
4. Count the links all the way around the track.
5. Check the arithmetic: pitch multiplied by links gives the inner circumference of the track.
6. Measure the width across the outside of the track.

Send us the model, serial number prefix and track size together and we will confirm the part before you order. Our guide to long pitch and short pitch rubber tracks explains why the pitch figure is the one most often misread.

TerraTrack or TerraTrack Plus for the 303.5

Both ranges are listed for the 303.5 family. TerraTrack is the standard range. TerraTrack Plus is the premium range, exclusive to Astrak, with toughened interlocking steel links, continuously wound anti-rust high tensile steel cords and an advanced abrasion-resistant rubber carcass. The interlocking links give it anti-detracking performance, worth having on a machine that works on slopes or turns on the spot all day. For the 303.5E, compare the TerraTrack track with the TerraTrack Plus track. Both carry the same 24-month warranty.

Wear and failure signs on CAT 303.5 tracks

Most rubber track problems announce themselves before the track fails.

• The track skips or jumps on the sprocket. Sharp and worn sprockets let the link slip or jump through the teeth, and that shock loading can damage the final drive motor. A sprocket cannot be measured against its own worn teeth, so compare it with an unused sprocket of the same type.
• The track runs slack, or suddenly looks far too tight. Both point at the track adjuster. Failed piston seals lose grease pressure and tension, and a broken spring rod makes the track look over-tight. Over-tension is a fault, not a safety margin. Our track tension guide covers how to check and adjust it.
• The track has come off. Tension, guidance or component wear is wrong, and often more than one at once. The documented causes are a failed track adjuster, worn sprockets or rollers, the wrong pitch, a packed undercarriage and operating habits that load one side of the machine, such as always turning the same way or working across a slope.
• Damage to the rubber itself. Cuts or missing rubber that expose the steel cords, and metal links that have broken away from the carcass, mean the track is at the end of its life.

A packed undercarriage accelerates all of this. Material packed between the rollers, links and sprocket teeth stops the components engaging correctly, so regular cleaning pays for itself in track life. Our article on why digger tracks come off covers each cause in turn.

Replacing the tracks: check the rest of the undercarriage first

New rubber tracks run on the sprocket, idler and bottom rollers already fitted. If any of those are worn, the new tracks wear faster and the detracking risk stays. Astrak supplies DuraTrack undercarriage parts and a Terrapart final drive for each 303.5 generation, so the whole track frame can be brought back to specification in one order. The parts below are the 303.5E CR listings; the other generations have their own.

Fitting a rubber track is a job for a fitter with the right equipment. Our approved plant fitters come to you anywhere within the UK through our onsite fitting service, and a free undercarriage inspection measures each component against its new dimensions. Wear on rollers and idlers is covered in its own guide.

What Astrak supplies for the CAT 303.5

For the CAT 303.5 family we list TerraTrack and TerraTrack Plus rubber tracks, DuraTrack sprockets, bottom rollers, top rollers and idler assemblies, and Terrapart final drives, each against the specific generation. The CAT rubber tracks, CAT sprockets and CAT final drives collections cover the other CAT models. Rubber tracks sold by Astrak UK carry a 24-month warranty. Tracks sold by Astrak US are covered by the Astrak US Product Warranty Policy.

See also the full rubber track range and our guide to rubber tracks or steel tracks.

Frequently asked questions

What size rubber tracks does a CAT 303.5 take?

Read the size moulded into the inside face of the existing track and quote it in full, as width x pitch x link count with any letter suffix. If it is not legible, measure the pitch centre to centre between two adjacent metal links, count the links and measure the width. Send that with the exact model, including the CR, C, D, E or E2 suffix, and the serial number prefix, and we will confirm the TerraTrack part.

Do all CAT 303.5 models use the same rubber tracks?

No. In our catalogue the 303.5 CR, 303.5C CR, 303.5D, 303.5D CR, 303.5E, 303.5E CR and 303.5E2 CR each have their own rubber track listing, and the Next Gen 303.5 CR with a CE9 or RE9 serial number prefix is listed separately. The 303.5 CR and the 303.5E are listed against different part references, so always tell us the generation and serial number prefix and confirm against the size on your existing track.

How many rubber tracks does a CAT 303.5 need?

Two, one per side. Our catalogue lists the quantity per machine as two for each CAT 303.5 rubber track and for the CAT 303.5 final drive.

Why do the tracks jump or come off my CAT 303.5?

Tracks come off when tension, guidance or component wear is wrong, and often more than one at once. The documented causes are a track adjuster that has lost tension, worn sprockets or rollers, the wrong pitch, a packed undercarriage and operating habits that load one side of the machine. Check the sprocket first when a track starts to skip.

CAT and Caterpillar are trademarks of Caterpillar Inc. Astrak Group develops and manufactures products intended to be compatible with machinery and equipment from various manufacturers. Unless indicated otherwise, Astrak parts are non-genuine replacement parts and Astrak Group has no relationship, commercial or otherwise, with the owners of the trademarks.