Cat® Undercarriage Part Guide

The undercarriage is a crucial component that supports and moves Cat^® heavy machinery.

This Cat undercarriage parts selection guide covers must-know information about undercarriage components and how to pick them for your track-type machine.

Overview of Cat Undercarriage Parts

Choosing undercarriage parts starts with understanding essential components and their functions.

Bushings and Pins

A bushing is the casing used on rotating or sliding machinery components. Pins and bushings work together to reduce friction and wear on moving parts.

Bushings: Bushings are cylinders for pins to slot into, allowing a circular motion that lets the machine maneuver over challenging terrain. They seal lubricant while keeping debris out.
Pins: These heat-treated pins connect the track, acting as a hinge with the bushing. They transfer loads between links and bushings and provide a lubricant reservoir.

Equalizer Bars

Equalizer bars control movement at the front of track roller frames, keeping tracks in contact with the ground. They also allow the roller frames to sway and shift on uneven surfaces.

Guards

The track guiding guards position the tracks. They protect internal components from debris, moisture and corrosion.

Idlers

Idlers are wheel-type components found at the front of the undercarriage. They feature internal reinforced plates for extended durability. Idlers maintain track tension for a steadier ride and reduced track wear.

Rollers

Rollers guide the machine while providing track tension.

Carrier or top rollers: These distribute track chain weight. A cylinder with a center bearing pivots on an axle, reducing friction. Carrier rollers are also known as top or upper rollers.
Track or bottom rollers: Track rollers support the machine’s weight on the ground. They direct the track chain around the idlers and sprockets to drive the unit forward.

Sprockets

The sprockets connect with the chain via a toothed wheel to create motion. They send power from the engine to the link assemblies, driving the vehicle forward. Cat sprockets resist bending and breaking with advanced surface, depth and core hardness.

Track Adjusters

The track adjuster and recoil mechanism maintain track tension and control. A hydraulic cylinder moves the idler to maintain proper tension while absorbing shock.

Track Assemblies

Tracks keep heavy vehicles moving over rough terrain. Cat tracks come in two types that suit different needs.

Rubber: These tracks suit jobs that require minimal ground disturbance. They have lighter treads than steel and customization options for specific terrains. Rubber tracks increase traction and operator efficiency while minimizing wear.
Steel: Unlike rubber, steel tracks have separate links, making replacement easier. Steel is more durable than rubber for harsh terrain. These tracks are ideal for equipment that needs a low center of gravity.

Track Links

Track links are part of the link assembly that provides the rail on which track-type machines run. Grease-lubricated components inside track links reduce friction. Lubrication increases internal wear and reduces undercarriage noise. Heat-treating the links increases surface, core and depth hardness.

Track Shoes

Track shoes support the heavy machine’s weight and maintain traction. Their design handles rocky or uneven terrain stress without bending or breaking. Track shoes come in various styles and widths, suiting moderate- to heavy-duty applications. Attributes include:

Penetration
Turning resistance
Traction control
Bending

How to Choose Cat Undercarriage Components

You must select undercarriage components to match the application and terrain. A reputable Cat dealer can recommend the ideal undercarriage for your needs, based on these factors.

Machine weight: A machine’s weight dictates its undercarriage size. Components on a compact track loader may not be suitable for a different machine of the same size. Travel distance, ground conditions and machine speeds play a part.
Machine application: Hydraulic excavator undercarriages are best for speeds under 3.5 mph. A crawler tractor configuration works well for machines traveling over 3.5 mph.
Undercarriage life span: Operating environment, vehicle speeds and functions impact undercarriage longevity. Shovels, backhoes or drills should work over the idlers and not the sprockets.

Before investing in an undercarriage, ask the following questions:

What is the machine’s ideal ownership period?
What are the total usage hours per week?
What are the ground conditions?
Are your applications low-, moderate- or high-impact?
Will the machine carry specialized attachments?
What are the typical grades and slopes on the jobsite?

Cat Abrasion™ Undercarriage

Cat Abrasion™ replaces SystemOne™. It exceeds the heavy-duty extended-life undercarriage for performance and longevity. This option is available for D3-D6 dozers. It suits low-to-medium-impact applications and high-abrasion materials.

The Cat Abrasion™ undercarriage offers the lowest cost-per-hour performance with extended wear.

General-Duty Undercarriage

These cost-effective undercarriages suit low-to-moderate-impact utility jobs. Rubber or steel tracks with increased flotation and low ground pressure offer stability. General-duty undercarriages provide a smoother, quieter ride.

This undercarriage is available for the following machines:

D6-D11 dozers
311-349 excavators
953-963 track loaders

Heavy-Duty Undercarriage

Heavier undercarriages suit moderate-to-high hard rock applications. Their life span is 20% longer than general-duty undercarriages. Steel tracks offer durability over even the rockiest terrain and resist cracking. Jobs benefiting from heavy-duty undercarriages include mining, demolition and pipe laying.

Machines with heavy-duty undercarriages include:

D9-D11 dozers
6015-6090 hydraulic mining shovels

Heavy-Duty Extended-Life

The HDXL undercarriage has a 20% to 40% extended life span compared to the heavy-duty undercarriage. DuraLink™ reduces idler scallop wear by adding material to the ends and center. This undercarriage is available for D9-D11 dozers.

Selecting Cat Undercarriage Parts

Cat designs general and heavy-duty components to be interchangeable. Universal parts minimize downtime and eliminate retrofitting.

Consider the following when buying undercarriage components.

Application

The maximum gross vehicle weight indicates its ideal application.

Light duty: Low GVW machines include pavers or mobile crushers. They have little to no travel and suit low-impact applications.
Medium duty: Machines such as blast hole drills have moderate movement and impact.
Heavy-duty: Crawler dozers or feller bunchers have high movement and impact.

Arrangement Type

Undercarriage frames may include a carbody or specific frame attachment design.

Base: The standard frame comes with complete left- and right-hand tracks only. The original equipment manufacturer provides the center section.
Bolt-on: A Cat upper structure bolted onto the track frames.
Carbody: A center frame welds to the track roller frames to allow the upper structure to pivot. Carbodies resist torsional bending and suit hydraulic excavators for medium-to-heavy-duty earth-moving applications.
Fixed: The upper structure mounts to this center-beam frame.
Oscillation: Roller track frames include pivot shafts and equalizer bars for rugged terrain.

Choose Bolt-On Sprockets

Some older machines have cast assembly and weld-on or bolt-on rims. Later models, including the 300 Series rxcavators, feature bolt-on one-piece sprockets. A weld-on adapter ring converts older sprocket segments to bolt-on. The benefits of bolt-on sprockets are:

Reduced misalignment risk.
Reversible segments improve sprocket longevity.
Replace sprockets without removing the track group.
Less maintenance and downtime replacing entire segments.

Check your machine’s manual for sprocket torque and bolt assembly specifications.

Select the Proper Track Shoe

Choose the narrowest track shoe that provides sufficient flotation to reduce wear. Wider shoes decrease the longevity of sprockets, track rollers and idler treads. Using the correct shoe width optimizes performance while lowering system cost.

Below are the track shoe types and features.

Single grouser shoes: These offer good penetration and traction but less maneuverability. Moderate-service single grousers work best in applications with low-to-medium impact and abrasion. Extreme-service shoes suit applications where moderate-service shoes bend or break. Super-extreme shoes offer maximum longevity in high-wear applications.
Multi-grouser shoes: Double or triple shoes provide less penetration with more maneuverability. Excavators and track-type loaders benefit from the reduced turning resistance for easier navigation.
Special shoes: Cat offers various specialized shoes that suit specific applications. Self-cleaning shoes separate, allowing debris from loose, muddy ground to fall out. Chopper shoes are ideal for demolition jobs needing compaction in demanding underfoot conditions. Steel mill flat shoes are low penetration and high wear for abrasive applications.
Track shoe supports: Hydraulic forestry excavators handle high-impact and extreme underfoot conditions. Roller-mounted track shoe supports reduce torsional loads to prevent link assembly damage.

Compare Track Rollers

The track roller shells wear along with the link. They don’t require maintenance during the original tread life. Two roller styles are available.

Single-flange: The rollers sit close to the sprocket. Low-sprocket loaders and tractors use single-flange rollers.
Double-flange: Some track-type tractors and loaders use double-flange rollers for improved track guidance.

Get Roller and Guiding Guards

Rocks and other debris may damage the track rollers, track and sprockets. Cat offers two roller guard options for your machine.

Full length: These include bolt-on wear strips. They cover the entire roller area with no room for guiding guards.
Partial length: Guiding guards protect the roller area.

Choose between the following guiding guard types:

End guiding guard: The end guard guides track entering or leaving the sprocket and idler. It prevents sprocket link gouging.
Segmented guiding guard: This center guard maintains track position while reducing link scuffing.
Full-length guiding guard: Total roller coverage maintains track alignment.

Guiding guards feature bolt-on wear strips for easy replacement.

Check the Working Pressure

The working pressure psi indicates the maximum pump relief valve pressure. Confirm a machine’s psi to decide whether general or heavy-duty undercarriage and components are more appropriate.

Light-duty applications: Low-to-moderate-impact excavators have a working pressure of 3,550 psi. An example of a light-duty machine is the Cat 303-305 CR Mini Hydraulic Excavator. Suitable applications include construction, trench digging and demolition work.
Heavy-duty applications: Machines like the Cat Class 330-375 excavators deliver 5,000 psi. They suit high-impact heavy construction and industrial projects.

Contact a certified Cat dealership to recommend parts for your specific applications.

Maintaining Cat Undercarriage Parts

Every Cat undercarriage works as a comprehensive system. Routine maintenance lowers operating costs while optimizing performance. Schedule an annual maintenance appointment with your Cat dealer. They can identify wear rates to determine the best servicing options.

Factors Affecting Undercarriage Wear

The terrain, job and material type affect the wear rate on undercarriage components. The machine’s function causes wear in the following areas.

Dozing and pushloading: Front-shifted weight increases wear on rollers and idlers.
Ripping and drawbar: Rollers, idlers and sprockets wear faster with back weight distribution.
Loading: Weight shifting from back to front impacts roller longevity.
Excavating: Components on the side of the digging wear down quicker.

Excavator Maintenance

Use these tips to keep excavator undercarriages in top condition.

Idlers: Ensure the machine moves forward to dig and work over the idler. Digging to the side or the rear increases idler wear.
Track shoes: Check for loose or missing bolts. The track shoes’ trailing and leading edges support each other. If one shoe bends, it will affect its neighbor. Repair or replace the damaged shoe before the problem escalates.
Track guards and guides: Replace damaged or bent guard guides. These keep the track aligned and can cause problems if they are not in top shape.
Sprockets: Check for oil leaks on the sprockets and final drive. Inspect the teeth for damage and tighten any loose bolts. Ensure the machine operates going forward with the sprockets in the back. Reversing increases wear.
Tracks: Examine the tracks for wear or material packed in the treads. Loosen debris by swinging the track above the ground and rolling it or clean it with a shovel.
Track tension: A too-tight track will wear down faster. Consult your manual for the correct tension based on the underfoot conditions.
Master drive: Inspect the machine rear for missing cotter pins that secure the bolts.
Idle machine: Unused machines risk seizing. Start it up every few months and exercise the track.

Dozer Maintenance

Inspect these components daily to get the optimum performance from a dozer.

Rollers: Check the top and bottom rollers for leaks or cracks in the shell. Ensure they’re free of debris — the carrier roller can stop spinning if materials get into it.
Idlers: Ensure correct shimming and check for wear.
Sprockets: Look for cracks, damage or chips and tighten bolts.
Track shoes: Examine the condition of the shoes. Look for missing bolts or lost hardware.
Guide guards: Confirm normal wear and that the guards don’t wear up into the bogey.
Tracks: Check proper track tension and limit high operating speeds to minimize wear.

Operation Tips

These tips will help prolong Cat undercarriage life:

Use the narrowest track shoe possible while ensuring sufficient flotation.
Switch the turning direction to minimize faster wear on one side of the undercarriage.
Reduce high operation speeds and avoid reversing unless necessary.
Pay attention to track spin, which increases wear and reduces component production.

Check your manual or contact a Cat dealer for more maintenance information.

Purchase Cat Undercarriage Parts From Gregory Poole Equipment Company

A Cat undercarriage system is the hub that keeps your machine performing at its best. It is an invaluable component accounting for 50% of fleet repair budgets. Gregory Poole is your trusted partner for undercarriage service and repair. As a certified dealer, we live and breathe all things Cat. We offer mobile repair services in the field to minimize downtime. Repair services range from track link rebuilding to frame realignment. If the undercarriage part you need is out of stock, we’ll source it in 24 hours.

Browse our locations to find a service provider near you, or call us at 800-451-7278 today.