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Excavator Final Drive and Planetary Gearbox Guide: Symptoms, Seals and Repair Choices

The travel gearbox is buried in the track frame, works in mud, and fails expensively when ignored. How to read the symptoms, what a floating seal does, and when to rebuild rather than replace.

Category Guide  ·  September 26, 2026  ·  Guangzhou, China

Excavator Final Drive and Planetary Gearbox Guide: Symptoms, Seals and Repair Choices

The final drive — the planetary gearbox bolted to the travel motor inside the track frame — is the only part of an excavator that works buried in mud, soaked in slurry, and shock-loaded every single cycle. It is also the part most often discovered too late, because a leaking final drive gives no fault code and no warning lamp. Understanding how these gearboxes fail, and what to order when they do, saves buyers some of the most expensive mistakes in the parts trade. Corbay is the international export brand of Guangzhou Shenyue Machinery Technology Co., Ltd., Guangzhou, China. Complete final drives, gear sets and floating seals for Kobelco, Komatsu, Hitachi, Doosan, Hyundai and other makes are quoted from Guangzhou daily, and this guide is how we walk buyers through the category.

The Symptoms — What a Failing Final Drive Looks Like

Oil around the sprocket or inside the track frame.The classic first sign. The gearbox is losing its oil through a worn floating seal, and every hour of work after that is wear on unprotected gears.
Grinding or clicking while travelling.Metal noise that changes with travel speed usually means gear or bearing damage already in progress — check the oil for glitter and metal particles.
One side slower than the other, or travel drift.Can be the travel motor rather than the gearbox; our travel motor guide covers how to separate the two before ordering either.
The machine will not move while the motor whines.Often a stripped sun gear or sheared shaft — the gearbox has stopped transmitting torque entirely.

How the Planetary Gearbox Is Built — and Why It Matters When Ordering

Excavator final drives are planetary reductions: a hydraulic travel motor spins a sun gear, which drives planet gears inside a ring gear, in one or two reduction stages. Smaller machines commonly use a single-row layout; larger machines step up to two rows for the greater reduction ratio. The layout matters when ordering because gear sets, carriers and housings are matched to the exact ratio — two gearboxes that look nearly identical from outside can carry different tooth counts inside. The casting number on the gearbox housing and the nameplate on the travel motor are the authorities; the machine model alone is not. On Kobelco machines, for example, the SK200-8 uses the Nabtesco GM38VB travel motor (assemblies under YN15V00037F1/F2/F3), while the SK200-10 and SK220XD-10 take the GM38VC under YN15V00083F1 — two generations that look alike and do not interchange. Our GM38VB travel motor page and GM38VC page show how we document the difference, and swing-side reductions such as YN32W00025F1 / YN32W00022F2 / YN32W00019F1 follow the same identification logic — see the swing reduction assembly page.

Floating Seals — Small Parts That Decide the Gearbox's Life

The floating seal — a pair of hardened metal rings with rubber torics, running in a tapered seat — is what keeps slurry out and oil in where the housing meets the rotating hub. It is a consumable: grit embeds in the seal faces, wear opens a film path, and oil escapes. Replacing floating seals early, with quality seal sets, is the cheapest final-drive maintenance there is. Bearings matter just as much: rebuild sets are only worth fitting with named-brand bearings, because a failed bearing in a final drive takes the gear teeth with it. The machine makers' own parts documentation shows how original reduction-gear references are structured — and that structure is what we cross-check against the casting numbers you send.

Rebuild with Parts or Replace the Assembly?

Rebuild with parts when the housing is sound: gear sets, shafts, bearings, thrust washers and floating seals are quoted line by line, and the repair typically costs a fraction of a new assembly.
Replace the assembly when the housing is cracked or badly scored, when tooth damage has spread metal through the whole unit, or when the machine must return to work in days rather than weeks.
Never mix unmapped gear sets.Ratio-matched gears must be replaced as a matched set — fitting one new sun gear against worn planets destroys both.
Fix the cause of the leak — a rebuild without new floating seals and a check of the hub seat is a repeat failure on schedule.

What We Need to Quote a Final Drive

Send five things to the team at Guangzhou Shenyue Machinery Technology Co., Ltd.: the part number or nameplate photo from the travel motor or gearbox housing, the machine model and serial number, the symptoms, the quantity, and the destination port. Quotations normally come back within 24 hours, with complete assemblies, gear sets, bearings and floating seal sets quoted as separate lines so you choose the repair depth yourself — genuine, OEM-quality and aftermarket grades stated openly on every line.

Final Drives and Gearboxes — FAQ

Do you supply final drive parts for brands other than Kobelco?Yes — complete assemblies, gear sets, shafts, bearings and floating seals are quoted across Komatsu, Hitachi, Doosan, Hyundai and other makes, identified from the gearbox casting number and the travel motor nameplate rather than the badge on the machine.
How long should a floating seal last?Seal life depends on the working ground — clean sites get years, abrasive mud can consume a set far faster. Inspect for oil film at every track service and replace the seals at the first sign of weeping, while the gearbox internals are still protected.
How do I request a quotation and how fast will I get a reply?Send the nameplate or casting number photo, machine model and serial, symptoms, quantity and destination port via the contact page — Guangzhou Shenyue Machinery Technology Co., Ltd. normally replies within 24 hours with every grade and repair option on the line.

Send the Casting Number Before the Gearbox Strips

A final drive never fails at a convenient moment, and it never fails cheaply once the oil is gone. Send the casting number, the nameplate photo and the machine serial, and the team at Guangzhou Shenyue Machinery Technology Co., Ltd. will confirm what fits, quote the assembly and the rebuild option side by side, and get the parts moving.

View Travel Motors & Gearboxes Send a Nameplate Photo

Corbay Excavator Parts is the international export brand of Shenyue Machinery (Guangzhou Shenyue Machinery Technology Co., Ltd.), Guangzhou, China. Shenyue is an independent parts specialist and is not affiliated with, or an authorized dealer of, Kobelco Limited. Parts are supplied as genuine, OEM or clearly identified aftermarket items, and the grade is stated on every quotation.