Why Excavator Travel Motors Fail in Pairs (And What Happens If You Replace Only One)

Few excavator failures create more confusion, arguments, and wasted money than final drive (travel motor) failures.

One side stops pulling.The other still “kind of works.”And the first instinct is always the same:

“Let’s just replace the bad one.”

That decision has killed more new travel motors than poor maintenance ever has.

This blog explains why travel motors fail in pairs, how load balancing and pressure differences accelerate damage, what case drain is really telling you, and why replacing only one motor often turns a repair into a repeat failure.

Understanding How Excavator Travel Motors Actually Work

Travel motors do not operate independently.

They are part of a closed mechanical and hydraulic relationship that includes:

• Two travel motors

• A shared pump circuit

• Cross-port reliefs

• Counterbalance and brake valves

• The undercarriage itself

When one side degrades, the other side doesn’t get a free pass.It gets overworked.

The Myth of the “Good Side”

One of the most dangerous phrases in excavator repair is:

“The other travel motor is still fine.”

What that usually means is:

• It hasn’t failed yet

• It’s compensating for the weak side

• It’s quietly accumulating damage

Travel motors don’t fail symmetrically in time — they fail symmetrically in cause.

Load Balancing: Why Both Motors Share the Pain

When an excavator travels, both motors are commanded to:

• Rotate at the same speed

• Produce similar torque

• Move the machine in a straight line

If one motor becomes weak due to:

• Internal leakage

• Worn rotating group

• Damaged valve block

…the system compensates automatically.

What Compensation Really Means

The hydraulic system:

• Increases pressure to maintain motion

• Forces the healthy motor to do more work

• Creates unequal torque distribution

The “good” motor now:

• Carries more load

• Sees higher pressure spikes

• Runs hotter

• Experiences accelerated wear

It doesn’t complain loudly.It just dies later.

Pressure Differences: The Silent Motor Killer

Excavator travel systems rely on balanced pressure between left and right circuits.

When one motor leaks internally:

• Pressure drops on that side

• Flow escapes through the worn motor

• The opposite motor sees increased resistance

This creates:

• Uneven pressure loading

• Repeated pressure spikes

• Shock loading through gears and pistons

Pressure imbalance is especially destructive during:

• Turning

• Counter-rotation

• Climbing

• Track correction under load

Why Travel Motors Hate Mismatches

Installing a new or rebuilt motor next to a worn one creates a mismatch problem.

What Mismatch Means in Real Life

A new motor:

• Has tight internal tolerances

• Minimal internal leakage

• Efficient torque conversion

A worn motor:

• Leaks internally

• Needs more flow to produce torque

• Bleeds pressure into heat

The system cannot satisfy both equally.

Result:

• The new motor is constantly forced to compensate

• Pressure climbs

• Case drain rises

• Heat builds rapidly

This is how new motors get murdered by old ones.

Case Drain Flow: The Most Ignored Warning Sign

Case drain is the clearest indicator of travel motor health.

What Case Drain Actually Measures

Case drain flow reflects:

• Internal leakage

• Wear between rotating components

• Seal condition

• Heat-related tolerance loss

A healthy travel motor:

• Has low, stable case drain

• Changes minimally with temperature

A failing motor:

• Shows rising case drain

• Spikes under load

• Increases rapidly when hot

What Happens When You Replace Only One Motor

Let’s walk through the most common real-world scenario.

Step 1: One Motor Fails Obviously

• Loss of pull on one side

• Track stalls under load

• Operator complains

Step 2: One Motor Is Replaced

• New or rebuilt motor installed

• Other side left untouched

• No system balancing performed

Step 3: Machine Feels “Better”

For a short time.

The new motor:

• Pulls harder

• Masks the worn motor’s weakness

• Absorbs pressure fluctuations

Step 4: Case Drain Climbs

On the new motor.

Because:

• It’s doing more work

• Pressure is uneven

• Heat increases internal leakage

Step 5: Second Failure

Usually within weeks or months.

And now:

• Two motors are bad

• The pump has been stressed

• The system is contaminated

All because the first decision was wrong.

Travel Motors Fail in Pairs Because Wear Is Shared

Even if only one side shows symptoms, both sides have usually experienced:

• The same hours

• The same oil

• The same contamination

• The same operating abuse

Differences in failure timing are normal.Differences in root cause are rare.

The Role of the Undercarriage (Often Ignored)

Undercarriage condition directly affects travel motor life.

Contributing Factors

• Uneven track tension

• Worn sprockets

• Binding rollers

• Misaligned frames

These issues:

• Increase rolling resistance

• Force one motor to work harder

• Accelerate paired failure patterns

Replacing one motor without addressing undercarriage load is pointless.

Pump Contribution: The Multiplier Effect

Travel motors don’t fail alone.

If one motor leaks internally:

• The pump compensates

• Flow demand increases

• Heat rises system-wide

This stresses:

• The opposite motor

• The pump

• The valve block

Paired failures are system failures, not component failures.

When Can You Replace Only One Travel Motor?

Rarely — but sometimes.

Single-motor replacement is only acceptable if:

• Case drain on the remaining motor is within OEM spec

• Both motors are pressure-tested

• Oil is clean

• Undercarriage is verified

• The failed motor was damaged by a known external event (e.g. impact)

Even then, it’s a risk — just a calculated one.

The Cost of Doing It Wrong

Replacing one motor instead of two may save money today.

But it often leads to:

• Second motor failure

• Repeat labour

• Pump damage

• Machine downtime

• Loss of trust

The most expensive repairs are the ones done twice.

Why Professionals Replace Travel Motors in Sets

Experienced mechanics and rebuilders know:

Balanced systems live longer.

Replacing travel motors in pairs:

• Restores pressure balance

• Equalises load sharing

• Reduces heat

• Protects the pump

• Extends overall system life

It’s not upselling.It’s system integrity.

Used Travel Motors: Why Matching Matters Even More

When buying used travel motors:

• Hours must be similar

• Condition must be comparable

• Case drain should be measured on both units

Mixing a “good used” motor with a tired one creates the same mismatch problem — just slower.

The Vikfin Position (Uncomfortable but Honest)

At Vikfin, we’d rather:

• Lose a single sale

• Than sell a part that causes a second failure

If one travel motor has failed:

• We strongly recommend evaluating both

• We will ask about case drain

• We will question imbalance

Because experience says what usually happens next.

Final Truth

Travel motors don’t fail alone.They fail together, even if one dies first.

Replacing only one doesn’t fix the system — it shifts the failure.

If you want reliability:

• Balance the load

• Match the components

• Respect the system

Because hydraulics always collect the debt — with interest.