Vehicle Bearings: Wheel Hub, Gearbox, Differential for Trucks & Buses — Codes & Maintenance

Vehicle bearings for trucks, buses, and special-purpose vehicles are a category of bearings engineered to withstand heavy loads, severe vibration, and continuous operation over long distances. A bearing failure on a commercial vehicle forces an unscheduled roadside stop — disrupting delivery schedules, creating traffic safety hazards, and inflicting costs that far exceed the price of the bearing itself.

Commercial trucks in Vietnam cover 150,000–300,000 km per year on roads of uneven quality — from National Highway 1A to subsiding provincial routes. Bearings must endure impact loading, heat from braking, and dust-and-water ingress. This article provides a detailed analysis of bearing codes by installation position, selection tables by vehicle weight class, and maintenance intervals by km — drawing on technical catalogs from SKF, FAG (Schaeffler), NTN, Timken, and real-world field data from Vietnamese transport fleets.

This article is a focused deep-dive within the Construction Equipment Bearings pillar, which covers bearings across all heavy equipment categories.

Five bearing groups on commercial vehicles

Trucks, buses, and special-purpose vehicles use bearings at five main groups of positions: wheel hubs, gearbox, rear-axle differential, drive shaft, and auxiliary systems (clutch, alternator, water pump). Each position demands a different bearing type — the wrong code leads to premature failure; the correct code extends service life by tens of thousands of kilometers.

1. Wheel hub bearings

The wheel hub is the highest-loaded position — the full weight of the vehicle and cargo bears down on the bearing through the axle spindle. Per ISO 492, truck wheel hub bearings must handle dynamic load ratings (C) ranging from 80 kN (light trucks) to over 350 kN (25-ton vehicles).

Bearing type: tapered roller bearings — 302xx, 322xx, and 332xx series depending on vehicle weight class. Tapered rollers handle simultaneous radial and axial loads during cornering — especially critical on mountain passes.

Wheel hub bearing codes by vehicle weight class:

Light trucks (1–3.5 ton) use the medium-sized 302xx series. Medium trucks (5–8 ton) step up to the 322xx series with a larger contact angle for better axial load capacity. Heavy trucks (18–25 ton) use the 332xx series — three-row rollers delivering superior load capacity but requiring larger hub assemblies.

Mounting configuration: non-driven front axle hubs use two tapered roller bearings mounted in opposition — the larger inner bearing carries the primary load, the smaller outer bearing provides secondary support. Axial clearance is set with a lock nut and lock washer.

Target axial clearance by weight class:

• 1–3.5 ton: 0.03–0.08 mm
• 5–8 ton: 0.05–0.10 mm
• 10–25 ton: 0.08–0.15 mm

Over-tightening creates bearing preload — increasing temperature, accelerating grease degradation, and reducing service life by 50–70%. Under-tightening causes wheel wobble and uneven raceway wear.

2. Gearbox bearings

A truck gearbox contains 15–25 bearings distributed across the input shaft, output shaft, countershaft, and reverse idler shaft. Each shaft uses a different bearing combination.

Bearing layout in a typical 6-speed gearbox (8–15 ton trucks):

The input shaft receives torque from the clutch — carrying radial and axial loads during gear engagement:

• Front end: cylindrical roller bearing NU2210 or NJ2210 — handles radial load while permitting thermal expansion
• Rear end: tapered roller bearing 32208 — handles combined loading and provides axial location

The output shaft transmits power to the differential — heavier loading than the input shaft in low gears:

• Front end: tapered roller bearing 32210 or 32211
• Rear end: tapered roller bearing 32212 — larger size to handle peak torque

The countershaft rotates continuously while the vehicle is moving — high radial load, minimal axial load:

• Both ends: cylindrical roller bearings NJ2212 or NU2212

Gearbox bearings run in oil — lubricated by the transmission fluid (GL-4 or GL-5). Service life depends directly on oil quality and change intervals. Contaminated oil contains metal particles from gear wear that abrade the bearing rolling surfaces.

Symptoms of gearbox bearing failure:

• Increased noise in a specific gear (bearing on the corresponding shaft is failing)
• Difficulty engaging gears or gear pop-out (excessive shaft play from worn bearings)
• High-speed vibration (shaft imbalance from bearing deterioration)

3. Differential bearings

The differential distributes torque from the drive shaft to both rear wheels — bearings here carry extremely heavy loads, especially during launch and hill climbing.

Differential bearing codes by vehicle weight:

The pinion bearings carry the highest load — particularly the front pinion bearing nearest the bevel gear. SKF recommends CL7C precision-class tapered rollers for heavy truck pinions (per SKF Heavy Truck Bearing Catalog).

Bevel gear backlash depends on pinion bearing position — when replacing bearings, backlash must be re-measured (0.15–0.25 mm) and adjusted using shims.

4. Drive shaft bearings

The drive shaft connects the gearbox to the differential. On long-wheelbase trucks, 2–3 drive shaft sections are joined by universal joints (cross joints) and supported by center bearings (carrier bearings).

Center bearing: uses deep groove ball bearings from the 6300 series — most commonly 6307, 6308, or 6309 depending on shaft diameter. The bearing is housed in a rubber mount that provides light self-alignment to compensate for minor misalignment.

Signs of center bearing failure: whole-body vibration at 60–80 km/h, humming from beneath the vehicle, cracked or sagging rubber mount.

Universal joint (cross joint): uses needle roller bearings in sealed cups. When failed, produces a "clunking" sound during launch or direction changes — replace the entire cross joint assembly.

5. Auxiliary systems

• Clutch release bearing: thrust bearing handling axial load when the clutch pedal is depressed. Common codes: 986813, 996713 (OEM-specific)
• Alternator: 6202, 6203 — small bearings, high speed
• Water pump: dedicated double-row bearing WB1630082, or 6204 + 6205 on older vehicles

Bearing code cross-reference by truck brand

Light trucks 1–3.5 ton

Medium trucks 5–8 ton

Heavy trucks 10–25 ton

See How to read bearing codes for a guide to understanding each character in a bearing designation.

Gearbox bearing layout — detailed description

A mechanical 6-speed truck gearbox (the type common on Hyundai HD, Hino FC/FG, and Isuzu FRR/FVR models) has a three-shaft architecture:

Input shaft — connected to the clutch disc, spinning at engine speed:

• Front end (clutch side): deep groove ball bearing 6210 or 6211 — provides axial location and handles light thrust loads
• Rear end (inside the gearbox): cylindrical roller bearing NU2210 — carries radial load while allowing axial sliding during thermal expansion

Countershaft — rotates continuously, transmitting power between gear pairs:

• Both ends: cylindrical roller bearings NJ2212 — high radial load, medium speed
• Some gearboxes use tapered roller bearings 32211 if helical gears generate axial thrust

Output shaft — connected to the drive shaft, carrying peak torque in first gear and reverse:

• Front end: tapered roller bearing 32210 — provides axial location and handles combined loading
• Rear end: tapered roller bearing 32212 — larger size because it is nearest the highest-loaded gear

In total, a 6-speed gearbox contains 6–8 main bearings plus 4–6 secondary bearings (synchronizer needle bearings, reverse idler bearings). During a gearbox overhaul, replace all main bearings — bearing cost represents only 15–20% of the total overhaul cost, but skipping them means the gearbox must be pulled apart again within months.

Maintenance schedule by km

Note: The intervals above apply to long-haul highway trucks. Urban delivery trucks (frequent stop-start, tight turns) should reduce intervals by 30% — for example, repack hub bearings at 55,000 km instead of 80,000 km.

Maintenance table by position and conditions

For detailed lubrication procedures, see Bearing lubrication. For general maintenance methodology, see Bearing maintenance.

Diagnosing vehicle bearing failures

Symptoms by position

Front wheel hub inspection procedure

1. Jack up the front axle, remove the wheel
2. Rock the brake drum (or hub) in two directions: lateral (radial load) and axial (thrust load)
3. Axial play exceeding 0.15 mm (light truck) or 0.2 mm (heavy truck) = adjustment or replacement needed
4. Spin the hub by hand — feel for rough spots, listen for grating
5. Remove lock nut + lock washer, pull the hub with bearings
6. Inspect raceways: uniform bright wear pattern = normal; spalling/pitting/rust = replace
7. Inspect the spindle surface: circular wear marks = recondition or replace spindle

Selecting replacement bearings

ISO standards and interchangeability

Truck bearings follow ISO 355 (tapered roller) and ISO 15 (cylindrical roller) standards. A 32218 from SKF, FAG, NTN, Timken, or ZVL all measure 90 × 160 × 42.5 mm with equivalent dynamic load ratings.

Differences between brands lie in:

• Steel quality: Japanese/EU brands use vacuum-degassed GCr15 or 100Cr6 bearing steel — L10 life 20–40% longer than generic alternatives
• Heat treatment: SKF uses XBITE technology, Timken uses case carburizing for heavy-duty bearings — improving impact resistance
• Cages and seals: stamped steel cages (standard) or machined brass cages (heavy load, high temperature)

ZVL Slovakia manufactures in the EU with steel and tolerances equivalent to SKF/FAG. In Vietnam, ZVL provides a reliable OEM-equivalent option at competitive European pricing — particularly suited for transport fleets replacing bearings in volume.

Common mistakes during truck bearing replacement

1. Hammering tapered rollers onto the shaft: causes brinelling — use a sleeve and hydraulic press
2. Reusing old hub seals: new bearing + old seal = water/dust ingress within 2,000 km
3. Skipping clearance measurement after installation: setting clearance "by feel" is the leading cause of premature failure
4. Mixing brands within the same hub: inner and outer bearings should be the same brand for consistent fit tolerances
5. Not replacing pinion shims: causes incorrect bevel gear backlash, noise, and accelerated gear wear

Vietnamese truck market — operating conditions and bearing impact

Major truck brands in Vietnam

The Vietnamese truck market is dominated by five brands:

• Hyundai (assembled by Thanh Cong): Porter II (1T), HD65/72 (2.5–3.5T), HD120 (5T), HD210/HD320 (15–25T) — largest market share in light and medium segments
• Hino (Japan): FC9 (6T), FG8 (8T), FM8 (15T), FL8 (16T) — durable, high-quality OEM bearings but premium pricing
• Isuzu: QKR (1.5–2.5T), FRR90 (6T), FVR34 (9T) — popular in the light and medium segments
• Fuso (Mitsubishi, Daimler): FI (5T), FJ (8T), FZ (25T) — strong in the medium segment
• Dongfeng: B180 (8T), KC (18–25T) — popular in the heavy segment due to low vehicle price, but OEM bearings often require early replacement

Vietnamese road conditions and bearing stress

Vietnamese roads impose higher stress on bearings than European or Japanese roads:

• National Highway 1A: uneven surfaces, potholes, subsidence — constant impact loading
• Mountain passes (Hai Van, Pha Din, Ma Pi Leng): tight corners generate high axial loads on hub bearings
• Monsoon flooding: water enters hubs through damaged seals, corroding raceways
• Overloading: many trucks carry 20–50% above rated capacity — bearing life drops exponentially (L10 life follows the (C/P)^(10/3) relationship)

Using the SKF bearing life formula: a truck loaded to its rated 8 tons on bearings with C = 190 kN achieves L10 life of approximately 250,000 km. The same truck carrying 12 tons (50% overload) sees life drop to approximately 90,000 km — under 40% of the rated-load figure.

Real-world case studies

Case 1 — Hyundai HD120 fleet on the North-South route

A transport company in Hai Phong operates 15 Hyundai HD120 (5-ton) trucks on the Hai Phong–Ho Chi Minh City route (1,700 km per trip, 4 trips per month, approximately 80,000 km per year). OEM hub bearings (Korean origin) lasted an average of 120,000 km — within specification, but replacement cost was high across the fleet.

Solution: switched to ZVL 32213 + 30211 for the front hubs. After 18 months of tracking (approximately 120,000 km): no truck required early replacement. Competitive European pricing reduced total hub maintenance cost across the 15-truck fleet substantially. Protocol: repack with lithium complex EP2 grease every 80,000 km, measure clearance every 50,000 km.

Case 2 — Dongfeng KC trucks hauling materials at highway construction

A contractor in Quang Ninh deployed 8 Dongfeng KC (25-ton) trucks hauling rock and earth at the Van Don–Mong Cai expressway project. Rough construction roads and chronic overloading (30–35 tons instead of 25 tons). Chinese OEM hub bearings failed at 40,000–50,000 km — severe spalling from overload and impact.

Solution: upgraded to tapered roller bearings 33220 (FAG or ZVL) with C = 380 kN — 15% higher than OEM. Combined with SKF hub seals replaced every 40,000 km and calcium sulfonate grease. Bearing life increased to 80,000+ km — double the OEM lifespan, despite continued overloading.

Case 3 — Hino passenger bus on the Hanoi–Lao Cai route

A bus operator on the Hanoi–Lao Cai route (300 km, mountain road) runs 6 Hino FC (29-seat) buses. Center bearing 6308 2RS failed at 60,000 km — vibration appearing at 70 km/h. Root cause: the O Quy Ho pass road has numerous potholes causing impact on the center bearing; simultaneously, the rubber mount softened in summer heat (40°C road surface temperature).

Solution: switched to ZVL 6308 2RS with C3 clearance (wider internal clearance for high-temperature operation) plus polyurethane rubber mount (stiffer than standard rubber). Life increased from 60,000 to 100,000+ km. Center bearing greased every 20,000 km instead of 30,000 km.

OEM bearing quality comparison by truck brand

Dongfeng holds a large share of the heavy truck segment in Vietnam due to low vehicle prices. However, Chinese OEM bearings typically have shorter service life — many fleet operators switch to FAG, NTN, or ZVL bearings at the first replacement interval.

Fleet bearing inventory management

Fleets of 10 or more trucks need minimum bearing stock to avoid vehicles waiting for parts. Recommended minimum inventory:

Order on a 3-month cycle — stock 20% above consumption rate. Browse tapered roller bearings and deep groove ball bearings at bacdanvongbi.com.

Emerging technology in vehicle bearings

Hub unit bearings (Gen 1–3)

Newer truck models (Hyundai HD from 2020, Hino 500 from 2019) are adopting hub unit bearings — integrating the bearing, seal, and hub into a single sealed assembly. Advantages: faster installation, no clearance adjustment needed, better water protection. Disadvantages: 3–5 times the cost of loose bearings, entire assembly must be replaced when the bearing fails.

• Gen 1: double tapered roller in a dedicated housing — still fits the existing spindle
• Gen 2: outer ring integrated with a mounting flange that bolts to the knuckle
• Gen 3: inner ring integrated with the axle shaft — most compact, but most expensive

In Vietnam, medium trucks (5–8 ton) are gradually transitioning to Gen 1 hub units. Heavy trucks (18–25 ton) largely remain on loose tapered roller bearings due to the heavy load requirements and field-serviceability demands.

Corrosion-resistant coated bearings

FAG (Schaeffler) offers Corrotect-coated tapered roller bearings — zinc-nickel plating for corrosion resistance, suited for trucks operating in coastal zones or hauling refrigerated cargo (condensation exposure). Timken produces the AP (All-Purpose) line with integrated seals for water protection. These cost 20–30% more than standard bearings but prove worthwhile for trucks running coastal routes like Hai Phong–Quang Ninh–Da Nang.

Key Takeaways

• Commercial vehicles have five main bearing groups: wheel hub (tapered 302xx/322xx/332xx), gearbox (NU/NJ + tapered), differential (32218–32222), drive shaft (6300 series), and auxiliary
• Hub bearing code depends on vehicle weight: 30210 (1–3.5T), 32213 (5–8T), 33220 (18–25T) — wrong size causes premature failure
• Vietnamese trucks commonly run overloaded — bearing life drops exponentially: 50% overload = 60% life reduction
• Repack front hub bearings every 80,000 km (highway) or 55,000 km (urban/construction)
• Gearbox bearing life depends on oil quality — change GL-4/GL-5 oil on the 50,000 km cycle
• ZVL and FAG are reliable OEM-equivalent alternatives for Dongfeng and Hyundai trucks — competitive European pricing with EU quality
• Fleets of 10+ trucks should maintain bearing safety stock — hub bearings and center bearings are the two priority stock groups
• Center bearings (6307/6308 2RS) are the easiest truck bearings to inspect and replace — no axle disassembly required

Related articles:

• Construction Equipment Bearings — Pillar
• Forklift Bearings
• Tapered Roller Bearings
• Bearing Maintenance
• How to Read Bearing Codes