Motor Grader Final Drive Replacement Cost: Cat 12M, Komatsu GD655, John Deere 672G, and More

Motor grader final drives, often called tandem drives, are the paired planetary reduction units in each rear axle that convert hydraulic motor output into traction. On a production grader running highway, road base, or mine haul rework, the tandem drives take continuous load through every pass. When one starts failing, you notice it in pull, blade force, and the machine's ability to hold grade on a slope. Here is what repair and replacement actually costs on the machines most commonly seen in road and site work.

Motor Grader Final Drive (Tandem Drive) Replacement Cost

Replacing or rebuilding a final drive unit on a production motor grader runs $5,500 to $18,000 all in, depending on whether the job is a planetary section rebuild versus a full drive replacement, and whether the hydraulic travel motor also requires service.

Repair Scope	Parts Cost	Total with Labor
Planetary gear section rebuild (seals, bearings, gears)	$2,500-$6,000	$5,500-$10,500
Full tandem drive replacement (reman)	$5,000-$10,000	$9,000-$16,000
Full drive plus travel motor replacement	$7,000-$13,000	$12,000-$18,000

Labor runs 10 to 18 hours on most production graders. The tandem drive assembly is a heavy unit, and access varies significantly by model. On a Cat 12M or 140M, the work requires removing significant structure around the rear axle to reach the drive assembly. Komatsu GD655 and John Deere 672G tandem drives are generally better-accessed, with slightly lower labor hours on the R&R portion.

Get a machine-specific cost range before calling shops: EquipBook's free repair cost estimator covers final drive and tandem drive repairs on most production motor grader models.

Cost by Model

Machine	Planetary Rebuild	Full Drive Replacement
Cat 12M / 12M3	$6,500-$10,500	$11,000-$16,000
Cat 140M / 140M3	$7,000-$11,000	$12,000-$18,000
Komatsu GD655-5 / GD655-6	$5,500-$9,500	$9,500-$14,500
John Deere 672G / 670G	$5,500-$9,000	$9,000-$14,000
Volvo G940B / G960B	$6,000-$10,000	$10,000-$15,500

Cat dealer parts on 12M and 140M models carry a significant premium over independent suppliers. Reman tandem drive assemblies for Cat graders are available through independent rebuilders at 30 to 50 percent below dealer part prices. Komatsu and John Deere have strong independent reman markets for their GD and G-series graders through both dealer-authorized and independent channels.

Signs a Motor Grader Tandem Drive Is Failing

Motor grader tandem drives give clear warning before they fail completely. Catching the problem early prevents contamination of the travel motor, which adds $3,000 to $5,000 to the total repair cost.

• Machine pulls to one side under load. On a slope or when pushing against a heavy windrow, the machine drifts toward the weaker drive side. One tandem is losing output efficiency. On flat ground at light load, tracking may still feel normal.
• Loss of grading power in one condition. The machine handles light work fine but loses significant traction force when making heavy cuts or climbing a grade. This is consistent with one tandem drive losing pressure efficiency while the other still works normally.
• Noise from one rear axle section. A grinding or whining sound from the tandem housing, especially at low speed under load, indicates internal gear wear or bearing failure. On a grader in a quiet environment, the noise is usually apparent during slow, high-torque passes.
• Metal in the tandem drive oil. Most production graders have service access to the tandem drive oil at major service intervals. Metal contamination in the oil is the earliest warning of planetary gear wear, often visible before any operating symptom appears. This is the check that prevents the most expensive outcomes.
• Oil leak at the tandem drive housing or axle seal. A wet drive housing means a seal has failed. Running the drive with low or contaminated oil accelerates gear and bearing wear. A seal replacement at first detection is far cheaper than a full drive rebuild after running it dry.
• Vibration through the rear axle at working speed. A rhythmic vibration through the rear frame during normal grading passes, particularly when the drive is loaded, can indicate planetary ring gear wear or sun gear damage inside the tandem housing.

Planetary Rebuild vs. Full Drive Replacement

The decision between a planetary rebuild and a full tandem drive replacement depends on what the inspection finds once the housing is open.

A planetary rebuild works when the ring gear, sun gear, and planetary carrier are within spec and only the bearings, seals, and potentially a set of worn planetary gears need replacement. If the internal gear teeth are in good shape, a rebuild is the right call and costs significantly less than a replacement.

A full drive replacement is the call when the ring gear has visible pitting or spalling, the planetary carrier has bearing damage that scored the carrier itself, or the internal gear geometry is out of spec. At that point, rebuilding around damaged castings is a short-term fix that fails again.

The travel motor is a separate unit that drives the planetary section. If the tandem drive failure was caused by a failing travel motor sending pressure spikes or low-flow conditions into the planetary section, the motor should be inspected and serviced at the same time. A fresh planetary rebuild on a marginal travel motor fails earlier than it should.

Does the Repair Make Sense?

A 2017 Cat 12M in good working condition is worth $200,000 to $300,000. A $9,000 planetary rebuild is 3 to 4 percent of that value. On production graders under 14,000 hours with solid circle gear, good tires, and a machine that earns consistent revenue, a tandem drive repair almost always makes sense.

The math is harder on older graders at 18,000 to 22,000 hours where the circle drive gear shows wear, tires are marginal, and blade wear is overdue. Before approving a $12,000 to $16,000 full drive replacement on a high-hour machine, know what that grader is worth on the market today.

Get a free motor grader valuation at EquipBook in under 60 seconds. Then use the free repair cost estimator to price the tandem drive repair on your specific machine. Those two numbers together tell you whether to repair it, get a second opinion on scope, or start looking at replacement.

See also: motor grader hydraulic pump replacement cost and motor grader repair costs overview for circle gear, engine, and other major repair ranges on the same machines.