Not sure which final drive fits your excavator? Measuring your existing final drive, travel motor or track motor is one of the most reliable ways to help identify the correct replacement, particularly when the original part number is missing or unreadable.
Whether you're replacing a final drive on a mini excavator, a 20-tonne machine or a compact track loader, getting the measurements right can save time, prevent ordering mistakes and reduce costly machine downtime.
At Pro Construction Parts, we specialise in supplying OEM and aftermarket final drives for excavators and construction machinery worldwide.
In this guide, we'll explain exactly what to measure, how to measure it and what information our team needs to help identify a suitable replacement.
Why Is It Important to Measure Your Final Drive?
Two final drives can look almost identical but have different mounting dimensions, hydraulic connections or internal specifications.
Even machines with the same model number may use different final drive assemblies depending on their production year, serial number or configuration.
An incorrectly matched final drive could result in:
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Mounting holes that don't align with the machine
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A drive sprocket that doesn't fit correctly
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Hydraulic ports in the wrong positions
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Incorrect hydraulic motor specifications
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Different travel speeds or gearbox reduction ratios
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Additional installation costs and unnecessary downtime
Important: Measurements are an essential part of identifying a replacement, but physical dimensions alone do not guarantee compatibility. The hydraulic motor specification, gearbox ratio and machine configuration must also be considered.
What Tools Do You Need?
Before starting, gather the following:
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Tape measure or vernier calipers
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Pen and paper to record dimensions
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Mobile phone or camera
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Access to the machine's make, model and serial number
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Existing final drive part number, if available
For accurate measurements, we recommend recording dimensions in millimetres (mm).
Always ensure the machine is safely isolated and supported before inspecting the final drive. Never work beneath an unsupported machine or track assembly.
Step 1: Measure the Sprocket Mounting Flange
The sprocket mounting flange is the circular section of the final drive where the drive sprocket attaches.
This is one of the most important areas to measure.
Record the following:
A. Number of sprocket mounting holes
Count the total number of bolt holes around the sprocket mounting flange.
B. Sprocket mounting PCD (Pitch Circle Diameter)
The PCD is the diameter of the imaginary circle passing through the centres of the mounting holes.
On a flange with an even number of equally spaced holes, you can usually measure directly between the centres of two opposite holes.
For other bolt patterns, the PCD may need to be calculated.
C. Sprocket bolt hole diameter
Measure the diameter of an individual mounting hole. Where threaded holes are present, identify the thread specification rather than relying on the visible hole diameter alone.
D. Sprocket flange outside diameter
Measure the overall external diameter of the mounting flange.
These measurements help determine whether the replacement final drive will correctly connect to the existing drive sprocket.
Step 2: Measure the Track Frame Mounting Flange
The track frame mounting flange is the section of the final drive that attaches to the excavator's undercarriage.
Like the sprocket flange, this section must match the machine's mounting arrangement.
Record:
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Number of mounting holes: Count the holes used to secure the drive to the track frame.
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Mounting PCD: Measure the pitch circle diameter of the mounting hole pattern.
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Bolt hole diameter: Record the hole size or thread specification, as applicable.
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Mounting flange outside diameter: Measure the overall diameter of the flange.
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Mounting register diameter: Where present, measure the locating shoulder or spigot that centres the drive in the track frame.
The mounting register is particularly important because it helps position the drive correctly and may not be obvious from photographs.
Step 3: Measure the Overall Height and Length
Next, measure the overall dimensions of the final drive assembly.
Depending on the design, the assembly may consist of a hydraulic travel motor attached to a planetary reduction gearbox.
Record:
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Overall axial length of the complete assembly
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Gearbox housing diameter
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Distance between the mounting faces
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Any protruding sections that may affect installation clearance
These measurements help confirm that the replacement unit will physically fit within the undercarriage.
Top tip: Take a photograph of the complete final drive from the side with a tape measure visible. This can be extremely useful when identifying an unfamiliar unit.
Step 4: Identify the Hydraulic Ports
The hydraulic connections are another essential part of final drive identification.
Most excavator travel motors have hydraulic connections for travel operation, while some also have separate case drain and speed-change connections.
Depending on the design, you may find:
Main hydraulic feed ports (A and B)
These supply hydraulic oil to operate the travel motor in either direction.
Case drain port
This allows internal leakage oil from the hydraulic motor case to return to the hydraulic system.
Two-speed or speed-change port
On applicable motors, this controls the travel motor's speed-changing mechanism.
Brake-related connections
Certain designs may have additional connections associated with brake control.
Record the number of ports, their locations, sizes and fitting types.
Do not assume the function of a port based on its size or position alone. Port arrangements vary between manufacturers, and incorrect hydraulic connections can cause serious damage.
If you're unsure, take clear photographs of the hydraulic connection block and send them to our team.
Step 5: Check the Final Drive Part Number
Before relying entirely on measurements, inspect the original final drive for an identification plate or stamped number.
Common final drive and travel motor manufacturers include:
The manufacturer's identification plate may contain a model code, serial number or assembly reference.
Even if the plate is damaged or partially unreadable, send us a photograph. The remaining characters may help identify the original unit.
Step 6: Confirm the Machine Make, Model and Serial Number
Alongside the final drive measurements, we'll need details of the machine.
For example:
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Make: Hitachi
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Model: ZX135US-5
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Machine serial number: As shown on the identification plate
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Required part: Complete final drive assembly
The serial number is especially useful because manufacturers sometimes change components during a model's production life.
A machine model alone is not always sufficient to identify the correct replacement.
Final Drive Measurement Checklist
Use the following checklist before contacting our team.
| Measurement | What to record |
|---|---|
| Sprocket mounting holes | Quantity |
| Sprocket mounting PCD | mm |
| Sprocket bolt hole size | mm / thread |
| Sprocket flange diameter | mm |
| Track frame mounting holes | Quantity |
| Track frame mounting PCD | mm |
| Track frame bolt hole size | mm / thread |
| Track frame flange diameter | mm |
| Mounting register diameter | mm |
| Overall assembly length | mm |
| Gearbox housing diameter | mm |
| Hydraulic connections | Quantity, sizes and positions |
| Original part number | If available |
| Machine make and model | Full model designation |
| Machine serial number | Full serial number |
You may not need every measurement for every machine. However, providing as much information as possible will help us identify the correct replacement more efficiently.
Can You Identify a Final Drive Without a Part Number?
Yes. In many cases, a final drive can be identified without its original part number.
Our team can use a combination of:
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Machine make and model
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Machine serial number
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Mounting dimensions
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Hydraulic port arrangement
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Photographs of the original assembly
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Existing motor or gearbox identification markings
For older excavators, imported machinery or machines with previously replaced components, this information can be particularly valuable.
However, some applications require further confirmation of hydraulic specifications and gearbox reduction ratios before a suitable replacement can be established.
Does a Replacement Final Drive Need to Be Exactly the Same Size?
Not necessarily.
OEM and aftermarket final drives can have differences in external housing design while still being suitable for the same machine.
The critical factors are correct mounting compatibility, sprocket alignment, hydraulic specifications, travel performance and any required braking functions.
For example, a replacement gearbox housing may have a slightly different outside diameter without affecting its installation or operation.
However, a different housing diameter does not automatically mean the internal gear ratio is different.
The gearbox reduction ratio must be verified independently.
Never assume that two final drives are interchangeable simply because their mounting dimensions match.
Common Mistakes When Measuring a Final Drive
Measuring the outside of the bolt holes instead of the centres
The PCD is measured through the centres of the bolt holes, not across their outer edges.
Confusing the sprocket flange with the track frame flange
These are separate mounting points and often have different dimensions.
Ignoring the hydraulic port arrangement
A final drive may physically fit but have incompatible hydraulic connections or motor specifications.
Assuming all machines of the same model use identical drives
Production changes and different machine configurations can affect compatibility.
Ordering based only on appearance
Two final drives can look nearly identical externally while having different internal specifications.
Frequently Asked Questions
How do I measure the PCD on a final drive?
For an even number of equally spaced mounting holes, measure from the centre of one hole to the centre of the directly opposite hole. For odd-numbered patterns, use an appropriate PCD calculation or measuring method.
Can I replace just the travel motor instead of the complete final drive?
In some cases, yes. If the hydraulic motor has failed but the planetary gearbox remains serviceable, replacing the motor alone may be possible. Compatibility must be confirmed before ordering.
Can I replace just the travel gearbox?
Yes, certain final drive assemblies allow the planetary reduction gearbox to be replaced separately. The original motor and gearbox interface must be compatible.
Are left-hand and right-hand final drives interchangeable?
Some machines use identical assemblies on both sides, while others have different configurations or installation requirements. Always confirm the correct application before ordering.
Can an aftermarket final drive replace an OEM unit?
Yes, provided the aftermarket unit has been correctly matched to the machine's mechanical and hydraulic specifications.
What if my final drive is still installed on the excavator?
You may be able to identify it using the machine serial number, existing part number and photographs. If measurements are required, some may only be accessible after removal. Never remove guards, hydraulic lines or mounting hardware without following the correct service procedures.
Need Help Identifying Your Final Drive?
At Pro Construction Parts, we supply OEM and aftermarket final drives, travel motors and travel gearboxes for a wide range of excavators and construction machinery.
We support customers across the USA, UK, Canada and international markets, with stock held in multiple locations.
Whether you have a part number, a complete set of measurements or simply a few photographs, our team can help you identify a suitable replacement.
Send us your machine details and final drive measurements for a quote.
