Excavator Travel Motor Problems: Test Before You Replace The Motor

A 13-tonne crawler machine tracks straight out of the yard on a cold morning. Two hours later, on the same flat pad and the same tracks, it bends to the left. The operator reports that the left side is "getting weak". The workshop orders a replacement travel motor, fits it, and the machine still pulls left.

Nothing about that sequence is unusual. The symptom is real; the conclusion is a guess. At least five components on a twin-track machine can slow one track or push a machine off line, and four of them are cheaper to fix than a motor. What separates a diagnosis from a guess is a short list of measurements taken at the same moment: pressure at both motor ports, oil temperature, and case drain flow.

Short answer

Do the left/right swap test before ordering anything. On most tracked machines the two travel circuits are mirror images, so swapping a suspect component from one side to the other tells you whether the fault follows the part or stays with the circuit; the same left/right logic is used whenever a suspect travel drive is compared against the drive on the other side of the machine. Then confirm the result with two numbers that a pressure gauge alone cannot give you: flow versus shaft speed, and case drain flow at working temperature. A travel motor is a replacement candidate when the fault moves with it in the swap test, when its volumetric efficiency has fallen below the published family value by a clear margin, and when the case drain trend rises with temperature. If pressure differential at the motor ports is below specification, or if the brake release pressure is low, the motor is usually a symptom rather than the cause.

what is published, and what still needs your data sheet

Numbers in this article carry one of four labels. Published means the value comes from a current BLINCE product record or a manufacturer technical document. Measured means it comes from the machine in front of you, with the measuring point named. Calculated means the arithmetic is shown. Confirm by data sheet means the answer depends on the exact model code, drawing or test procedure and cannot be settled from a family table.

The BLINCE travel motor families publish three anchors that are useful during diagnosis. Rated pressure is 25 MPa and maximum pressure is 31.5 MPa across the low-speed high-torque families, from the small HMS02/HMSE02 group through the heavy HMCR05/HMCRE05 group. The published torque column at a 10 MPa pressure differential gives a direct arithmetic check on the motor's own displacement, which is the fastest way to confirm that the motor on the machine is the size the nameplate claims. Displacement, rated torque, rated speed and power rise together across the range. An HMS02-0 is published at 213 mL/rev and 848 N·m; an HMCR05-0 at 470 mL/rev and 1,510 N·m; an HMS50-2 at 4,997 mL/rev and 19,863 N·m. Those are family reference values, not a selection for your machine. Two published codes show how far apart the ends of that range sit: the HMS02/HMSE02 radial piston travel motor for compact drives, and the MCR05 series radial piston travel motor for heavier undercarriages.

Published by BLINCE product data (captured 2026-08-31): displacement, pressure, torque, speed and power ranges for the HMS02/HMSE02, HMS05/HMSE05, HMS08/HMSE08, HMCR03/HMCRE03, HMCR05/HMCRE05, HMCR10/HMCRE10, HMK18/HMKE18 and HMS50 series. The same records show a table-label irregularity in the small HMS02/HMSE02 group, where the "rated torque" row reads higher than the "maximum torque" row for two sizes. Where a family table contains an internal inconsistency like that, treat the individual torque cell as unconfirmed and use the displacement and pressure rows, which are consistent across every family, until the exact data sheet is in your hand. A published range is a starting point rather than an approval: the radial piston travel drive group shows how those families are arranged, and the comparison between a travel motor and a slew motor explains why two drives can look similar in a catalogue and still be built for different duty.

Confirm by data sheet: the exact permissible case drain pressure at the drain port, the required brake release pressure and release timing, the shaft, flange, port and spline interfaces of the selected code, and whether the machine uses a single-speed or a two-speed travel motor with symmetric or asymmetric distribution. The travel motor category groups the low-speed high-torque options that reach the undercarriage, while the wider hydraulic motor range shows where those drives sit next to orbital, gear and piston motors in the same catalogue, and the published displacement, torque and speed variables are what any selection check has to compare.

What is actually in a travel circuit

A travel motor does not act alone. On the machines that generate most "travel motor problems" complaints, the drive path runs from one side of a tandem or two-pump arrangement, through a travel control section, through a centre joint (the rotary union that carries oil from the upper structure down to the undercarriage), into a brake valve, into the motor, and then into a planetary or direct final drive. Any one of those stages can slow a track, and the machine will look identical from the cab in every case. The radial piston architecture used by most low-speed travel drives and the general layout of hydraulic drives on construction machinery together explain why the centre joint and the final drive belong in the same diagnosis as the motor.

It helps to separate the circuit into two halves. Everything upstream of the motor — pump, relief, control spool, centre joint — decides how much flow arrives and at what pressure. Everything downstream — brake release, motor, final drive, track — decides how much of that flow reaches the ground as traction. Pay particular attention to the centre joint on a tracked machine. A worn rotary seal there produces exactly the internal-leakage signature that a worn motor produces, and it does so while staying invisible from both the cab and the engine bay. That is also why a gauge teed in at the wrong place misleads so easily; the test points that produce false readings are worth reviewing before any of the numbers below are trusted, and a motor under suspicion should be judged against the published case drain pressure limit rather than by appearance.

The practical purpose of the swap test below is to decide which half of that circuit owns the fault. For background on how the drive path is laid out on construction machines, the BLINCE overview of hydraulic drives on construction machinery is a useful orientation, and the travel motor category page shows how the low-speed high-torque drive options are grouped.

Five travel complaints and where each one usually starts

The wording of the complaint carries information. "It pulls left when hot" and "it never had power from new" are different faults with different histories, and treating them as one topic wastes parts and time.

Read the table as a routing tool, not as a diagnosis. Each row names the measurement that separates the candidates, and the last column names what still has to be confirmed before money moves.

The test that decides: swap the left and right travel circuits

Most tracked machines give you a free experiment. The left and right travel circuits are designed to be identical, so a component that is suspected of being worn can be exchanged with its counterpart on the other side. If the symptom moves with the component, the component owns the fault. If the symptom stays on the original track, the fault is in the circuit that feeds it, and the motor was never the problem.

Which parts can be swapped depends on the architecture, and the machine's own manual or service procedure controls the sequence and the safety measures. On machines with separately piped travel motors, hoses can sometimes be crossed between the two motors; on machines where the brake release and two-speed pilot lines are shared or electrically controlled, only the relief cartridges, or the control sections, may be movable. Where the choice is between a radial piston travel drive and another architecture, the comparison between a travel motor and a slew motor and the machine's own displacement, torque and speed requirements are the two questions to settle first. Two rules matter more than the method itself: the machine has to be blocked and supported before any hose is opened, and a tracked machine's travel circuit has to be depressurised by the approved procedure with the engine stopped. A swap test on a machine that steers by varying travel flow can also damage components if it is run with the tracks on the ground, so the approved test conditions come from the machine documentation. A workshop shortcut is not a substitute for them.

Run the test at the same oil temperature in both directions, and record the result as a difference between the two sides rather than as a single value: for example, the left motor gains 6 % more speed after the swap while the right loses 6 %. A one-sided change of that shape is far more convincing than any single gauge reading.

Calculation 1: flow versus speed shows how much of the oil is leaking inside

A travel motor converts flow into rotation. The conversion is described by displacement, and the shortcut version of the relationship is:

Q (L/min) = D (mL/rev) × n (r/min) ÷ 1000

Take a machine fitted with a 470 mL/rev travel motor, which is the displacement of the HMCR05-0 code in the BLINCE heavy travel motor family, and suppose the operator keeps full travel engaged until the track reaches a steady 125 r/min measured at the motor shaft or at the final drive with the reduction ratio divided out.

Step 1 — theoretical flow.

Q_th = 470 × 125 ÷ 1000 = 58.75 L/min

Step 2 — measured flow. Suppose an inline flow meter in the supply line to that motor shows 70 L/min at the same oil temperature and the same track speed. That measurement is Measured; the arithmetic that follows is Calculated.

Step 3 — volumetric efficiency.

η_v = Q_th ÷ Q_measured = 58.75 ÷ 70 = 0.84 → 84 %

Step 4 — interpretation. About 16 % of the oil going into the motor is not producing rotation. Some of that loss is normal, because every motor leaks a little across its clearances, and the amount rises as oil gets thinner with heat. The BLINCE travel motor records publish a volumetric efficiency of 92 % or better for these families, so a measured 84 % at normal working temperature is 8 points below the family claim, and the missing flow has to go somewhere. It leaves through the case drain — the plumbing rule behind that port is explained in why motors need a case drain and many pumps do not — or it returns across the worn faces of the gerotor set and the distributor, which is one of the failure modes reviewed in the guide to what fails first in a low-speed high-torque motor.

Step 5 — the action this changes. Before condemning the motor, repeat the measurement on the opposite track at the same temperature. Two tracks at 91 % and 84 % point at the low side. Two tracks at 85 % and 84 % point upstream, because a single worn pump or a restricted centre joint can starve both motors equally. In general engineering practice, efficiency differences between two otherwise identical circuits are more reliable evidence than an absolute number, because the absolute number depends on a test condition that a family table rarely defines exactly; when the two tracks agree but travel is still weak, the ordinary causes and test methods for a slow or weak motor and the placement of the test points are the next two things to re-check.

Calculation 2: pressure differential tells you whether the motor is being asked to do work it cannot deliver

Hydraulic motors develop torque from the difference between the pressure at the inlet port and the pressure at the outlet port. The usable form of that relationship, with pressure in bar and displacement in cm³/rev, is:

T (N·m) = Δp (bar) × D (cm³/rev) ÷ 62.8

The same BLINCE family table gives you a way to check the arithmetic against published data, which is a useful habit before you trust either number on the machine. For the HMCR05-0 code at a 10 MPa pressure differential, which is 100 bar:

T = 100 × 470 ÷ 62.8 = 748.4 N·m

The published theoretical torque for that code at the same 10 MPa differential is 747 N·m. The 0.2 % difference is rounding, and it confirms that the published displacement and the published torque column describe the same motor.

Now run the same arithmetic on a loaded machine. Suppose the travel circuit holds 250 bar at the motor inlet and 220 bar at the outlet during a steady climb, giving a pressure differential of 30 bar. At 470 mL/rev:

T = 30 × 470 ÷ 62.8 = 224.5 N·m

That is a small fraction of the 1,510 N·m the family publishes as continuous torque at 25 MPa, and it is the correct answer to a different question than the one the symptom asks. A motor that cannot climb is not short of torque capacity; it is short of pressure differential. The useful comparison is between the differential the machine should be able to produce at the relief setting and the differential it actually produces, measured at both ports at the same moment. Measuring only the inlet pressure tells you what the relief valve is doing, not what the motor is receiving. The 470 mL/rev displacement used above belongs to the MCR05 series radial piston travel motor, and the same torque relationship applies across the radial piston travel drive range whenever displacement and pressure differential are known.

This is where a proper test point pays for itself. A gauge teed into the supply line near the valve block reads the relief setting, while a gauge at the motor inlet reads the pressure after line and centre-joint losses. The BLINCE guide to pressure gauge placement and false readings explains why the two readings diverge, and the wider framework for a motor that runs slow or weak carries the same logic through pump, valve and motor causes. Matching a replacement motor to the load is a separate exercise from diagnosing the one on the machine, and the published sizing variables are what a quotation has to be checked against once the diagnosis is done.

Case drain flow: the leakage trend that matters more than the number

Case drain flow is the oil that escapes past the internal clearances of the motor and leaves through the drain port instead of doing work. It is the most direct wear indicator available on a machine in service, and it is also the easiest one to misread, because a normal motor and a worn motor both produce a measurable drain flow that rises as oil temperature rises.

Three conditions turn a case-drain reading into evidence. The oil temperature must be recorded at the same moment, because a motor that drains 3 L/min at 40 °C and 9 L/min at 70 °C is telling a different story from one that drains 9 L/min at both. The drain line must be open and unrestricted, because a partly blocked drain hose raises drain pressure — the port itself exists for exactly this reason, as the comparison between motors and pumps explains — and pushes oil past the shaft seal instead of through the drain. And the drain pressure at the port must stay inside the limit published for the specific motor. That limit is model-specific, and no family table can substitute for it.

What you are looking for is the shape of the change. A drain flow that is stable across a warm-up cycle, similar on both tracks, and consistent across repeated tests points away from wear. A drain flow that climbs with temperature and sits clearly higher on one side than the other matches the same motor that lost volumetric efficiency in Calculation 1, and the two measurements together are a much stronger case for replacement than either one alone. If that pattern holds, compare it with the general symptom list for a motor that runs slow or weak and with the failure sequence reported for low-speed high-torque motors before the evidence is treated as complete.

The brake release circuit: the quiet cause of drag, heat and slow travel

Travel motors that hold a machine on a slope usually do it with a spring-applied, pressure-released brake. The spring holds the brake closed; hydraulic pressure from the release circuit pushes it open. When everything is correct, the brake is fully open before the machine moves. When release pressure is low, or when a seal in the release piston has failed, the brake disc drags even though the operator has commanded travel.

The signature of a dragging brake overlaps almost completely with the signature of a worn motor: the machine is slow, the hydraulic oil and the motor housing run hot, and the case drain flow can rise because the extra load raises temperature. The test that separates them is a pressure measurement at the release port against the pressure published for that motor, taken at the moment travel is commanded, using the test-point rules that apply to any pressure check. Heat that appears on both tracks, with no pressure difference between them, is a cooling and duty question rather than a drive question, and the cooler sizing method applies to it. If the release pressure is correct and the brake still drags, the release piston or the brake itself has to come apart.

The same logic applies to the counterbalance and holding functions. A motor that runs away under load, or that allows a load to creep down, is describing a holding-circuit problem rather than a loss of motor torque, and the fix is in the valve and brake arrangement. The BLINCE analysis of a winch motor that runs away under load walks through counterbalance, brake release and anti-cavitation behaviour in that order, and the same sequence applies when a travel drive will not hold on a ramp. On drives where the brake is built into the travel motor assembly, the release function and the drive function share one housing, so both have to be checked together rather than as separate items.

Heat, oil condition and contamination

Oil temperature is not a diagnostic detail; it is part of the measurement. Internal leakage, hydraulic-mechanical losses and a dragging brake all convert energy into heat, and heat thins the oil, which increases leakage again. A test run that starts cold and finishes hot can produce two different verdicts on an unchanged motor, which is why every comparison in this article is specified at one temperature.

Oil condition changes the arithmetic as well. Water, air and hard particles all reduce the film thickness the motor's internal clearances depend on, and the particles left behind by a failed motor travel through the whole circuit. Fitting a replacement motor into a circuit that still carries debris from the failed one is one of the most expensive sequences in mobile hydraulics, because the second failure is usually charged to the same motor. The BLINCE contamination control guide covers cleanliness targets and the checks that follow a component failure, and the oil cooler sizing guide covers the case where temperature rises because the heat has nowhere to go rather than because a component is failing.

Repair or replace: the tradeoffs that decide the order

Once the fault is confirmed to be inside the motor, three routes open, and they are not interchangeable.

Start with the least expensive option that can actually cure the fault. An external reseal addresses oil escaping from the shaft seal or a joint face, and it addresses nothing else. The reason a leaking shaft seal and a rising drain flow can be two different faults is set out in the guide to shaft seal leakage and repeat motor failure. If the leakage is internal, or if the drive splines and the gerotor set are worn, a reseal returns a leaking but still worn motor to service, and the second failure generally arrives sooner than the first — which is why the guide to what fails first in a low-speed high-torque motor is worth reading before the seal kit is ordered. A reseal is the right answer when the motor has low running hours, the case drain trend is flat, efficiency is at family expectation, and the leak is visible and external.

Replacing the motor is the route most buyers reach for first, and it carries the most hidden risk. Performance figures are easy to compare; interfaces are not. Flange pattern, output shaft or spline, port positions and thread forms, two-speed distribution, brake release pressure and timing, and any speed or temperature sensor the machine's controller expects all have to match. The BLINCE HMS02/HMSE02 radial piston travel motor and the heavier MCR05 series radial piston travel motor are published as low-speed high-torque travel drives with 25 MPa rated and 31.5 MPa maximum pressure; whether a specific code is a drop-in for your machine depends on the drawing comparison, not on the family name. If the machine is a wheeled drive, or needs more travel speed than a radial piston unit provides, the travel motor and slew motor comparison helps separate the architectures before the part number conversation starts.

Circuit repairs are the route that rarely gets the attention it deserves. Centre-joint seals, relief cartridges, control spools and brake release pistons all cost less than a motor, and every one of them can produce a travel symptom that looks like motor wear. This route only becomes visible through the swap test and the pressure measurements, which is why those two steps come before any order.

What to measure on the machine before you order a motor

Measurements taken once, cold, prove very little. Build the picture from a warm machine under load, and write each value next to its oil temperature and its measuring point.

Pressure side: inlet and outlet pressure at both travel motors, recorded simultaneously under the same load; the pressure differential that results; the relief setting measured at the valve block; and the pressure drop between the valve block and the motor inlet, which is where centre-joint and line losses appear.

Flow side: supply flow to the motor with an inline flow meter, or case drain flow collected over a timed interval with a measuring container, on both tracks, at the same temperature. Shaft or final-drive speed at the same moment, divided by the reduction ratio if the measurement is taken at the sprocket.

Brake and control side: release pressure at the release port, release timing, two-speed pilot pressure where fitted, and the machine's own static holding test where the manual provides one.

Condition side: oil temperature trend, oil level, filter condition, water or air entrainment, and a sample for cleanliness analysis. Any debris found in the filter or the case drain line belongs in the container too, because the material and the particle shape point at the failed surface.

Documentation side: the complete model code of the existing motor, the machine model and serial number, and photographs of the nameplate, the mounting flange, the shaft or spline, and every port.

Common mistakes, and what each one costs

Raising the relief pressure to cure weak travel is the habit in this list that costs the most, and the one that appears most often. It looks reasonable because the pressure gauge is the only instrument on many machines, and a higher setting does restore a little force — briefly. The pressure that the relief valve passes is pressure that is no longer producing rotation, so the system runs hotter, thinner oil leaks past the same clearances faster, and the motor reaches the end of its life sooner. The check that should come first is the pressure differential at the motor, not the setting at the relief, together with the general test sequence for a weak hydraulic motor.

Replacing the motor without a swap test is the second. The test costs a few hours and usually a set of new seals; the mistake costs a motor, a second haulage, and a machine that still pulls left, which is exactly the sequence in the opening paragraph of this article.

Comparing two tracks at different temperatures, or on a slope, or with different track tension, is a third. A track that is tighter than its partner consumes more power, and a machine tested on a side slope loads the two tracks unequally by design. Flat, even ground and matched tension are part of the test setup, not a detail after it.

Judging on a single case-drain number is the fourth. Without a temperature record, a second track for comparison, and a check that the drain line is open, a drain measurement can support almost any conclusion the person reading it already holds.

Reusing the oil after a motor failure is the fifth, and its consequence is visible in the next failure rather than this one. The debris that a failed gerotor set or bearing produces does not settle out of the system by itself.

Finally, ordering from a family name rather than a drawing is a mistake that only appears at installation. A published family covers displacement, pressure, speed, torque and power ranges; it does not promise that a flange, shaft, port pattern or two-speed distribution matches a specific machine. The BLINCE motor sizing guide covers the selection variables, and the low-speed high-torque motor review of what fails first explains why the interface detail, not the headline torque figure, decides whether a replacement works.

Who should stop before ordering anything

Do not order a replacement travel motor on the strength of a symptom description, a family table, or a single pressure reading. Stop and gather evidence when the complete model code cannot be read or confirmed, when the machine's travel circuit diagram is unavailable and the pipework has been modified, or when the failure occurred in a holding or braking function rather than in driven travel.

Pause the purchase and let a qualified person take over when the machine works on a slope, lifts or carries a suspended load, or performs a function where a travel drive failure creates a personnel hazard; when the machine is under warranty or a service agreement that a non-approved part may void; or when the travel function is electronically controlled, with proportional valves, travel speed sensors, slip control or an anti-stall strategy that will not accept a mechanically different motor. In all of those cases the machine manual, the approved data sheet and the manufacturer's own test procedure control, and this article's measurements are inputs to that process rather than a substitute for it.

There is one more honest boundary. If travel is weak while the machine is also operating another function, or if the symptom only appears on a gradient with a bucket load, the fault may sit in the load-sharing or flow-sharing behaviour of the whole system rather than in either travel circuit. In that situation, one more pressure measurement taken during combined operation is worth more than any further work on the motor itself.

Data to send for a travel motor review or quotation

If the measurements point at the motor, group the information so that a supplier can check interfaces and duty in one pass rather than asking for the same field twice.

Machine and drive: machine make, model and serial number; the function the drive performs; single-speed or two-speed; wheeled or tracked; whether the machine works on gradients.

Existing motor: complete model code from the nameplate; displacement; rated and maximum pressure as marked; brake type; output form; and the reduction ratio of the final drive if it is a separate unit.

Measured performance: inlet and outlet pressure at the motor under load, with the oil temperature at the time of measurement; pressure differential; case drain flow with its temperature; supply flow and motor speed where a flow meter was available; brake release pressure; relief setting.

Interfaces: photographs of the nameplate, mounting flange, output shaft or spline, and every port and connector; the port thread standard; the position of the drain port; the presence of speed, temperature or pressure sensors.

Circuit and condition: travel circuit diagram or a marked photograph of the pipework; oil grade and viscosity; system cleanliness or a recent oil analysis; what was replaced before, and what happened afterwards.

Evidence: the swap-test result, the case-drain containers or readings from both sides, and any debris recovered from the filter or drain line.

FAQ

How do I know if my excavator travel motor is worn out?

The strongest evidence is the combination of three signs taken at working temperature: the fault follows the motor when the left and right travel circuits are swapped, the flow-versus-speed calculation shows volumetric efficiency clearly below the published family value, and the case drain flow is higher on that motor and climbs with temperature. Any one of them alone is suggestive, and none of them is conclusive.

Can I just replace the seal kit instead of the whole motor?

Yes, if the leak is external, the case drain trend is flat, the efficiency calculation is at expectation and the hours are low. A seal kit cannot restore a worn gerotor set, distributor face or drive spline, so on a high-hour motor the reseal often becomes a short delay rather than a repair.

Why does my machine track straight when cold and pull to one side when hot?

Because leakage depends on viscosity. Cold oil is thick and leaks less; warm oil is thin and passes the worn clearances faster. That is also why a cold test can pass a worn motor, and why every comparison in this procedure has to be made at a recorded oil temperature.

What case drain flow is normal?

There is no universal number. The limit belongs to the specific motor and comes with its data sheet, and the practical evidence is the trend at temperature plus the comparison between two identical circuits. A drain line that is restricted, or a drain pressure above the published limit, distorts the reading before the motor does.

Can a low relief setting cause weak travel and a hot motor?

A relief setting below the circuit's design pressure reduces the pressure differential available at the motor, so travel becomes weak, and the flow that the relief passes becomes heat. In that case the motor is working with what the valve gives it. Confirm the relief setting and the pressure differential at the motor ports before deciding anything about the motor.

What do you need to quote a replacement travel motor?

The complete model code of the existing motor, machine make and model, displacement and marked pressures, the mounting flange, shaft or spline and port arrangement, the brake type, and whether the drive is single-speed or two-speed. Measurements and photographs shorten the review; without the interface detail, a quotation is only a preliminary one.

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✉️ Email: sales16@blince.com

Website: https://blince.com/

Disclaimer

This article is a general engineering guide. Final component selection should be based on machine drawings, measured hydraulic data, working conditions, safety requirements, and confirmation from a qualified hydraulic engineer or supplier.

Blince Hydraulic Team

Blince Hydraulic is an industry-leading company dedicated to precision-engineered fluid power manufacturing and custom hydraulic solutions. Backed by decades of deep field expertise in industrial machinery and thousands of successful global deployments, our engineering team focuses entirely on high-performance hydraulic component manufacturing, including specialized orbital motors, high-pressure travel drives motor, and robust directional control valves. Our production infrastructure utilizes state-of-the-art multi-axis CNC machining systems and is fully ISO 9001 certified to guarantee repeatable volumetric accuracy across every single manufacturing run.

We deliver fast, highly dependable, and cost-efficient hydraulic solutions to heavy industry distributors, machinery OEMs, and maintenance crews across more than 150 countries. Whether your active project calls for a small-volume batch of customized shaft profiles or a large-scale production run of severe-duty cast iron gear pump, we configure our flexible production schedules to meet your target lead times with total pricing predictability. Partnering with Blince means securing maximum system efficiency, elite material quality, and uncompromised fluid power professionalism.

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