Goal: Repair a planetary (hub/axle) gearset on a Hino FG17/FG19-style truck. This guide explains every component, theory, symptoms, inspection and step-by-step repair/rebuild instructions for a beginner mechanic. Use the Hino workshop manual for all torque values, service limits, and part numbers — I provide procedures and how/why things are done, not manufacturer-specific torque/spec tables.

Safety first (short): safely jack and support the vehicle on stands, chock wheels, wear eye/hand protection, use lifting gear for heavy parts, drain fluids on a catch tray, keep the work area clean. Some components are heavy/spring-loaded — proceed carefully.

Quick overview (what planetary gear here does)
- Many Hino FG-series rear axles and hub-reduction axles use a planetary reduction gearset inside the wheel hub or final drive. Purpose: multiply torque, reduce speed at the wheel, allow compact packaging, spread load across multiple gear teeth.
- Main parts: ring gear (often integrated with hub), sun gear, multiple planet gears (mounted on a carrier), planet bearings/bushings, planet carrier, output flange or axle shaft, bearings, seals, shims, circlips/snap rings, retaining nuts/bolts, gearbox/differential case (if internal planetary). Also bearings and races that support rotational loads.

Components — detailed descriptions
- Ring gear: large internal-toothed gear; often fixed to the hub or carrier. It forms the outer boundary and meshes with planet gears.
- Sun gear: central gear around the axle; planets mesh around it. Its rotation relative to the carrier and ring controls output ratio.
- Planet gears (planets): typically 3–6 small gears that orbit the sun gear. Each has its own pin/bearing and shares load with others.
- Planet shafts/pins or needle bearings: the pivot/axle for each planet gear inside the carrier.
- Planet carrier: holds planet gears and transfers torque to the wheel/axle or to the final output.
- Bearings: tapered/roller or ball bearings support axial/radial loads of the carrier, sun, and hub.
- Seals/gaskets: keep lubricant in and contaminants out (axle seals, hub seals).
- Shims/adjustment washers: used to set end-play/backlash and bearing preload.
- Snap rings, retaining nuts, bolts, lock tabs: hold components in position.
- Lubricant: heavy gear oil in final drive or grease in hub; essential for lubrication and cooling.

Theory of operation — plain language + analogies
- Imagine the sun gear is a lamp post at the center, planets are children walking around holding hands with the post (meshing), and the ring gear is a fence around the playground. When you push the children (rotate the planets), the whole assembly moves differently depending on which part is held fixed and which is driven. Planetary gearsets allow reduction (torque up, speed down) by using the relationships between sun, planets, and ring.
- Load sharing: planets share torque among multiple teeth — like several people carrying a heavy box together. If one person is weak (worn/broken), the rest take more load, accelerate wear.
- Backlash and preload: backlash is the intentional small gap between gear teeth (like a little play in a door hinge). Too much backlash causes clunking and shock loads; too little causes binding and overheating. Bearing preload (how tight the bearings are stacked) is like tightening the nut on a wheel bearing: too loose = play; too tight = heat/wear.

Why this repair is needed (symptoms & causes)
Common symptoms that indicate planetary/hub problems:
- Growling/whining noise at certain speeds — worn gear teeth or bearings.
- Clunking when accelerating or backing off — excessive backlash or broken tooth.
- Vibration in drive or wheel — worn bearings, damaged planets.
- Wheel play or lateral movement — bearing wear or worn carrier bearings.
- Leakage of gear oil or grease — failed seals.
- Metal particles in drain plug/magnetic plug — sign of internal wear.

Root causes:
- Lack of lubrication or contaminated lubricant (water, dirt) → pitting, scoring.
- Overheating (overloaded, low oil) → softening, spalling.
- Impact / road shock → chipped/broken teeth, bent shafts.
- Bearing failure from contamination, misassembly, or preload error.
- Improper assembly, wrong shims or torque → wrong backlash/preload → accelerated wear.

Tools and supplies you’ll need
- Full socket and wrench set, breaker bar, impact gun (if available)
- Torque wrench (calibrated)
- Pullers (hub puller, bearing puller)
- Press or hydraulic press, bearing drivers
- Snap-ring/circlip pliers
- Dial indicator (for measuring backlash and runout)
- Feeler gauges, straight edge
- Micrometer, caliper
- Hammer, brass drift, soft mallet
- Cleaning solvent, brushes, lint-free rags
- Parts trays and labels
- Replacement bearings, seals, shims, planet gears, ring gear/sun gear as needed
- Gear oil or hub grease as specified by Hino
- Assembly lubricant (gear oil or assembly grease)
- Seal driver, gasket maker if needed
- Safety gear (gloves, glasses, jack stands, wheel chocks)

Diagnosis & inspection (what to do before tearing down)
1. Road/bench test: note speeds and conditions of noise or vibration.
2. Check gear oil level and condition. Look for metal flakes on drain plug or magnet.
3. Jack and support vehicle, remove wheel and brake components as needed. Check wheel bearing play.
4. Spin the hub by hand (with the brakes off) to feel roughness or binding.
5. Use a pry bar to check axial play and a dial indicator to measure backlash between ring and sun (when possible without disassembly).
6. If noises, metal in oil, or play found → proceed to disassemble.

Disassembly — general step-by-step
Note: Sequence will vary by hub/axle layout. Label/photograph everything as you remove it so reassembly is accurate.

1. Prep: Clean around hub and brake area. Drain final drive/hub lubricant into catch pan.
2. Remove wheel, brake caliper/assembly, rotor/drum, ABS sensor, and dust cap as needed.
3. Remove hub retaining nut/lock washer and any retaining bolts. Use impact or breaker as required. Secure the axle so it doesn’t turn.
4. Pull the hub/drive flange off. Use puller/slide hammer as needed. Be careful not to damage spline or seal surfaces.
5. Expose planetary assembly: remove hub carrier cover or axle flange nuts/bolts. Take out retaining bolts securing carrier or ring gear. Keep bolts in order.
6. Remove ring gear/hub assembly to expose planet gears and carrier. In some designs the ring is part of the hub—treat as one piece.
7. Remove snap rings and planet shafts/pins. Slide out planet gears; note each gear’s orientation.
8. Remove carrier from output shaft. Take off sun gear if accessible.
9. Extract bearings and races from hub/carrier. Press out bearings where necessary.
10. Keep components labeled by position (e.g., planet 1, planet 2) if you want to compare wear patterns.

Inspection — what to look for and how to measure
Clean all parts with solvent and dry thoroughly.

Gears:
- Visual: look for pitting, spalling, chipped or broken teeth, scoring, discoloration (overheat).
- Feel: teeth should be smooth and uniform.
- Measure: compare tooth thickness and profile to service limits (manual). Look for eccentric wear and wear direction.

Bearings:
- Spin each bearing by hand: roughness, grinding, or rough spots = replace.
- Check rollers and cages for wear, spalling.
- Inspect races for discoloration, pitting.
- Replace bearings if any doubt — bearings are cheap vs. failure.

Planet shafts/pins:
- Check for wear, flat spots where roller meets pin, excessive runout.
- Replace worn pins or bushings.

Carrier and sun gear:
- Check bores for ovality, scoring; check bolt holes for elongation.
- Inspect sun gear for tooth wear.

Seals & shims:
- All seals should be replaced. Shims must be measured and recorded; they determine backlash/end play.

Backlash and runout:
- Use dial indicator on gear teeth to measure backlash. Compare to spec. Excessive/backlash uneven indicates wear or wrong shim stack.

Common faults & fixes
- Pitted/spalled teeth: replace affected gear (sun, ring, planets); if widespread, replace entire assembly.
- Broken/chipped tooth: inspect mating gear for damage; replace both if necessary.
- Bearing failure: replace bearing and race. Replace seals too; check shaft surfaces for wear that could shorten bearing life.
- Excessive play or end-play: adjust shims or bearing preload during reassembly to spec.
- Contaminated oil: clean housing thoroughly; replace seals and all bearings/gear parts as necessary.
- Uneven wear patterns on planets: indicates misalignment; inspect carrier bores and sun gear alignment. Replace worn parts and correct shim settings.

Reassembly — general best practices
1. Cleanliness: very important — planet gears and bearings need a clean environment. Use lint-free rags and solvent.
2. Replace all seals and all bearings recommended (don’t reuse bearings).
3. Use assembly lube on bearings and gear contact surfaces during reassembly.
4. Reinstall sun gear into position; install carrier with new bearings where needed.
5. Install planets into carrier on their pins/shafts with correct orientation; secure with snap rings.
6. Install ring gear/hub assembly. Torque bolts in star pattern to lock it in place (use manual spec).
7. Set shims and preload: this is critical.
- Bearing preload: usually set via shims/adjustment nut. Preload prevents play but must not over-torque bearings. Use torque wrench or bearing preload tool per manual.
- Backlash: measure with dial indicator on gear teeth while rotating one component; adjust shims to get specified backlash.
- Typical method: add/remove thin shims between carrier and housing until dial indicator reads within spec. Re-test after tightening bolts to final torque.
8. Reinstall hub/drum/rotor and brake components; torque wheel nuts to spec.
9. Install new seals carefully using a driver, seating them square to prevent leaks.
10. Refill final drive/hub with correct gear oil to specified level.
11. Rotate assembly several revolutions by hand to distribute lubricant and check for binding, noise, or irregular motion.

Adjustment notes — setting backlash and preload (conceptual)
- Backlash measured as tooth-to-tooth movement when trying to rock the ring gear back and forth; adjust shims to reduce or increase as needed.
- Bearing preload often determined by turning torque (measured with a calibrated torque wrench adapter or by feeling with known method in manual). Preload should be enough to remove play but not so tight as to overheat.
- If you don’t have precise tools, don’t guess — wrong preload kills bearings quickly. Refer to Hino torque/preload procedure or have a shop with a torque-angle/torque-check fixture help.

Testing after rebuild
- Spin the hub by hand, listen for smooth rotation.
- Check for play with a pry bar.
- Road test at low speed first, listen for noise, heat checks after short run, then re-check torque on major fasteners and oil level.
- After 100–200 km, re-torque wheel/hub bolts and re-check for leaks or noises.

What can go wrong if done incorrectly
- Incorrect shim stacks or preload → premature bearing and gear failure.
- Reusing old seals/bearings → leaks and contamination → repeated failure.
- Wrong lubricant or wrong fill level → overheating, pitting, gear failure.
- Improper torque on ring gear bolts → loosening and catastrophic damage.
- Contamination during assembly → rapid wear.
- Misaligned or damaged parts left in service → vibration and broken teeth.

Practical tips and analogies for a beginner
- Think of the gearset like a small team of workers (planet gears). If one worker is injured (worn), the rest suffer more — replace all worn planets rather than a single one if damage is widespread.
- Shims are like shims under a door hinge to adjust how snug the door closes. Too many or too few shims cause binding or rattle.
- Preload is like tightening a bicycle headset: snug enough to remove play, not so tight you can’t turn. If you over-tighten, things wear quickly.
- Label everything and take photos step-by-step. Reassembling a planetary hub upside-down or with a pin reversed is a common beginner mistake.
- When in doubt, replace bearings, seals, and fasteners. It’s cheaper than a second repair due to a bad rebuild.

When to stop and consult a pro
- If you cannot measure and set backlash or bearing preload with repeatable confidence.
- If major components (ring gear, sun gear, carrier) are damaged and it’s unclear which parts must be matched for proper tooth contact — some gears are matched/paired.
- If you lack a press or bearing removal tools — forcing parts can damage housings or spline shafts.
- If the repair requires welding/press-fitting that you can’t verify per manual.

Final reminders
- Use the Hino FG-series workshop manual for specific torque specs, shim thickness charts, and bearing preload targets.
- Replace oil seals and bearings whenever you open the hub; cleanliness and correct preload/backlash are the two most critical points.
- Test and re-check: run the vehicle, then re-inspect fasteners, leak points, and give a final road check.

This covers theory, every key component, diagnostic checks, detailed disassembly/inspection/reassembly sequence, what goes wrong, and practical beginner tips. Follow the Hino service manual for exact specs and tolerances.
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From the Archives: Hino FG Series Old footage of the Hino FG Series truck.

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Summary (why this repair matters)
- The starter motor is the electrical/mechanical link that turns the engine over so it can begin running under its own compression and fuel. If the starter fails you’ll get no crank, slow crank, grinding, or it may stick on — any of which can leave a truck stranded or damage the flywheel teeth. Fixing or rebuilding the starter restores reliable cranking and protects the flywheel and electrical system.

How the system works — plain-language theory and analogy
- Analogy: the starter is a powerful sprinter (motor + reduction gears) that pushes the engine to take the first few steps. The solenoid is the coach who moves the sprinter up to the starting line and connects him to the power supply. The ring gear (on the flywheel) is the first step the sprinter grabs to pull the whole body (engine) into motion. The overrunning clutch (Bendix or one-way clutch) is like a slip-coupling that lets the sprinter disengage once the engine runs faster than the starter.
- Electrical: turning the ignition to START sends 12 V from the battery through ignition/starter circuit to the starter solenoid. The solenoid closes the high-current contacts and simultaneously pushes the pinion gear to mesh with the flywheel ring gear. High current flows from the battery directly into the starter motor windings, producing torque and turning the pinion which turns the engine.
- Mechanical: many heavy-duty starters (such as used on Hino FG17/FG19) are reduction-type: the motor spins fast but low torque is multiplied through a small gearbox so the pinion turns slower and with greater torque to crank a diesel engine. The overrunning clutch prevents damage when the engine suddenly runs faster than the starter.

Major components (full practical list with detailed description)
1. Battery and main cables
- 12 V (or 24 V on some trucks) battery supplies the starter. Heavy-gauge positive cable goes to the starter main terminal; a ground/negative cable returns to the chassis/engine block.
- Clean, low-resistance connections are critical.

2. Ignition/starter control wiring and starter relay (starter solenoid coil circuit)
- Low-current circuit activated by the ignition key (or start relay) that energises the starter solenoid coil.
- Includes neutral/park safety switches and fuses or fusible links.

3. Starter solenoid (integral to many starters)
- Acts as a high-current relay and a mechanical actuator: when energized it closes the large contact to feed battery current to the motor, and it pushes the drive pinion into mesh with the ring gear. Inside: solenoid coil, plunger, return spring, high-current contacts.

4. Starter motor housing (yoke) and end-caps
- Rigid enclosure holding the armature and field components; contains mounting flange and bolt holes.

5. Field windings or permanent magnets
- Create the static magnetic field the armature interacts with. Older starters use wound field coils; modern ones often use permanent magnets.

6. Armature (rotor)
- Rotating core with laminated steel, winding coils, and commutator segments. When current flows, the armature produces torque.

7. Commutator
- Copper segments on the armature that transfer current from the stationary brushes to the armature windings. Needs to be clean and not grooved or burnt.

8. Brushes and brush holder assembly (carbon brushes + springs)
- Carbon blocks that press on the commutator to route current to the armature. Wear over time and require replacement.

9. Bearings / bushings (front and rear)
- Support the armature shaft; bronze bushings or needle/ball bearings. Wear causes excessive movement, noise, poor contact.

10. Drive pinion (pinion gear)
- Small gear that meshes with the flywheel ring gear to turn the engine. It’s attached to the armature or the reduction gearbox output.

11. Overrunning clutch / Bendix drive / reduction gearbox
- Overrunning clutch: lets the pinion spin freely if the engine drives the pinion (protects starter). Reduction gearbox uses planetary gears to increase torque—common on diesel starters for trucks.

12. Shift fork or lever (if external) and return spring
- Moves the pinion into/out of mesh (or the solenoid does this internally).

13. Nose cone / drive end housing
- Houses pinion and bearings; often contains oil seals.

14. Flywheel ring gear
- Mounted on flywheel/torque converter/flexplate; the starter pinion engages these teeth. Damaged teeth indicate engagement problems.

15. Mounting bolts and alignment dowels
- Secure starter to bellhousing; alignment is critical to prevent gear clash and tooth wear.

16. Miscellaneous: heat shields, dust covers, wiring terminals, sheathes, shims (if alignment required), fusible links/fuses.

Common failure modes (what can go wrong)
- No crank at all:
- Dead/weak battery, bad battery cables/terminals, blown fusible link, failed solenoid coil, broken ignition switch, open safety interlock.
- Click but no crank:
- Solenoid energizes but high-current contacts or motor windings defective, or very weak battery/high voltage drop.
- Slow cranking:
- Weak battery, high resistance in cables/terminals, worn brushes, contaminated commutator, bad bearings, internal short in motor.
- Grinding / gear clash:
- Worn/damaged ring gear teeth, misaligned starter mounting, broken pinion teeth, solenoid failing to fully engage pinion before motor spins.
- Starter stays engaged after engine starts:
- Sticking solenoid plunger, failed return spring, damaged overrunning clutch — can cause severe overrun damage.
- Intermittent operation:
- Loose wiring, corroded terminals, worn brushes, intermittent solenoid contacts.
- Smoke or burning smell:
- Prolonged cranking, internal short, overheated windings, burnt commutator — starter can be destroyed.

Tools and supplies you’ll need
- Basic hand tools: metric sockets and wrenches, extension bars
- Torque wrench
- Multimeter (voltage and continuity)
- Battery load/test or jumper pack
- Starter bench tester or variable power supply (12 V or 24 V depending)
- Screwdrivers, pliers, drift punches
- Wire brush, emery cloth (for terminals and small commutator dressing)
- Solvent/parts cleaner, lint-free rags
- Replacement parts: brush set, bushings/bearings, solenoid (or entire starter), pinion/overrunning clutch if required, seals, grease (high-temp, moly), anti-seize
- Safety gear: gloves, eye protection

Step-by-step workshop procedure — remove, inspect, repair, reinstall (beginner-friendly, safe order)
Note: follow Hino FG17/FG19 service manual torque values and specific removal notes. If unsure of torque or steps, consult official manual.

1) Safety and preparation
- Park on level ground, chock wheels, set parking brake.
- Isolate electrical: disconnect NEGATIVE battery terminal first, then positive if needed. This avoids short and unintentional cranking.
- Wear gloves + eye protection.
- If the truck has an air starter or dual batteries, make sure both are isolated per service manual.

2) Access and removal
- Locate starter: on Hino FG17/FG19 it’s mounted to the bellhousing near the flywheel (passenger side on many Hino diesels). It’s heavy—support it when removing.
- Label and photograph all wire connections so reassembly is exact.
- Remove small control wire(s) first (remove nut/bolt on solenoid terminal), then large battery positive cable (main terminal). Protect battery cable end from touching ground.
- Remove mounting bolts (usually two or three). Support starter as last bolt is broken free.
- Wiggle and withdraw starter. On tight fits, remove any heat shields or nearby components (exhaust, brackets) as needed.

3) Bench inspection and basic tests (before full teardown)
- Visual: check for oil contamination (engine leaks can soak starter), corrosion, damaged terminals, scorched components, stripped pinion teeth.
- Bench test (if you have a safe bench setup): connect battery or bench supply to the main terminal and ground starter body. Jumper the small solenoid terminal to main positive briefly. The pinion should extend and the motor should spin strongly. If it doesn’t engage, solenoid or actuator may be bad. If it spins but pinion doesn’t engage, the shift mechanism or overrunning clutch may be faulty.
- Electrical checks: use multimeter to check continuity of solenoid coil and resistance of motor windings (compare to spec if available). Large shorts (near zero ohms) or opens indicate failure.

4) Disassembly (typical reduction-type starter)
- Remove solenoid from starter body: unscrew mounting screws. Note spacer/shims.
- Remove end cap(s) — unscrew screws or bolts holding the rear cover.
- Remove brush holder assembly: brush springs and brushes usually press out or unscrew. Mark brush orientation/fit.
- Slide armature out of housing carefully. Inspect commutator for grooves, burning, high wear.
- Remove front nose cone to access pinion and overrunning clutch. This may require removing circlips or snap rings.
- Inspect bearings/bushings at both ends. Press out worn bearings or replace bushings as required.
- Inspect reduction gear set for wear, broken teeth, or heavy pitting.
- Inspect solenoid plunger and high-current contacts for pitting and wear. Replace contact disc if burnt.

5) Cleaning, measurement, and parts replacement
- Clean all parts in solvent; dry thoroughly.
- Commutator: minor glazing can be cleaned with very fine emery sandpaper; do not remove much metal. Deep grooving/damage means turn on lathe or replace armature.
- Brushes: replace if length is below specification or springs weak. Always replace as a set.
- Bearings/bushings: replace if there is axial/runout play or rough rotation. Bronze bushings often need to be replaced; press-fit ball/needle bearings need replacement.
- Overrunning clutch/pinion: if it does not freewheel or has play, replace.
- Solenoid contacts: replace if pitted, burned, or welded.
- If oil contamination present, find and fix engine oil leak; replace seals.

6) Reassembly and lubrication
- Use correct grease sparingly on bushings (manufacturer-recommended grease for starters and pinion splines). Never grease the commutator or brushes.
- Reinstall armature carefully, ensuring bearings seat properly.
- Refit brush assembly and ensure brushes move freely in holders and spring properly load each brush.
- Reassemble solenoid and ensure plunger moves smoothly with return spring.
- Replace seals, gaskets, dust covers.

7) Bench test after rebuild
- Again, bench-test: solenoid engages, pinion extends reliably, motor spins strongly. Listen for grinding, growl or abnormal noise. Observe for smoke (immediate stop if smoke).
- Perform a voltage drop/current draw test if you have an ammeter clamp: typical good starter draw should be within manufacturer spec; very high draw indicates internal short/worn brushes/dragging bearings.

8) Reinstall starter on vehicle
- Clean bellhousing face and ring gear area; inspect ring gear for tooth damage.
- Position starter, align dowels, hand-start mounting bolts to avoid cross-threading.
- Torque mounting bolts to Hino spec (refer to service manual).
- Reconnect battery positive cable to starter main terminal; reconnect control wire(s) to solenoid; ensure all terminals are tight and insulated.
- Reconnect battery (positive last, negative first when removing; reverse to reconnect negative last? Standard: reconnect positive, then negative. But safest: positive then negative; main point: ensure proper reconnection sequence and no accidental grounding).
- Test crank: key to START, observe engagement, cranking speed, noise. If anything abnormal stop and isolate.

Diagnostics and troubleshooting quick guide
- No click at all: check battery voltage at starter with ignition in START; if battery voltage present and solenoid not clicking, check solenoid coil continuity and ground; check ignition/start switch and safety interlocks.
- Click but no spin: solenoid engaging but motor not receiving current — check high-current contact in solenoid, battery cable to starter, internal motor winding open.
- Motor spins but pinion does not extend: check solenoid shift mechanism and pinion assembly or linkage.
- Slow but strong click: voltage drop under load — check battery state-of-charge, cable resistance (voltage drop test across battery positive to starter), poor ground.
- Grinding: stop immediately — inspect ring gear and pinion; verify proper clearance and starter mounted correctly.

Preventive maintenance tips
- Keep battery terminals clean and tight; corrosion increases voltage drop.
- Check starter wiring and insulation periodically.
- Protect starter from oil contamination; fix engine leaks.
- If you replace a starter, check ring gear condition; a new starter can wear on a damaged ring gear and fail quickly.
- Replace worn brushes and bushings early when symptoms of sluggish cranking appear.

Safety notes (short)
- Disconnect battery before working on starter. Heavy currents and metal tools can cause sparks and injury.
- Support starter when removing — it’s heavy.
- Do not bench-test a starter near combustible solvents or closed spaces; sparks occur.
- If replacement parts require press-fit or lathe work, use proper equipment or have a machine shop perform it.

Final practical pointers specific to Hino FG17/FG19 (shop reality)
- Hino trucks typically use a reduction-type starter with integrated solenoid; expect a heavier assembly and a pinion with overrunning clutch.
- Mounting location near bellhousing requires safe jacking or lift to access; remove heat shields or pipes for clearance if needed.
- Always verify battery system voltage and condition before condemning the starter — many “starter” failures are battery or wiring issues.

This covers the full starter system, each main component, why failures happen, what to look for, and a step-by-step workshop-style repair/rebuild path suitable for a beginner mechanic. Follow the Hino service manual for torque values, wiring diagrams, and model-specific notes.
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