Quick summary
- What this is: replacing the torque converter (TC) that sits between the engine crank and the marine transmission on Hino W04D / W04C-T / W04C-TI engines.
- Why: the TC transfers torque via fluid; when it fails (slip, shudder, noise, contamination) drivability and safety are affected. The job requires separating the transmission from the engine, removing the old converter, inspecting mating parts, and installing a new one correctly and priming it.
- Read the Hino Marine Workshop manual for exact bolt torques, fluid type and capacity, and any model-specific steps. Below is a detailed beginner-level walkthrough with component descriptions, theory, common failure modes, tools, safety, step-by-step removal/installation, and checks.

Safety first (must-do)
- Work on a dry, stable dock/bench with engine/transmission supported on rated engine/transmission stands or the ship’s mounts.
- Block the prop and secure vessel; disconnect the battery and shore power.
- Drain oil/ATF into labeled containers and dispose of per local regs.
- Use engine hoist/transmission jack rated for the weights; never rely on jacks alone—use stands.
- Wear eye protection, gloves, and steel-toe boots. Beware of sharp fins and heavy components.
- Never run the engine with the torque converter removed or with the converter empty of fluid.

Theory and simple analogy
- The torque converter is a fluid coupling that multiplies torque at low speed and smoothly transfers power from the crank to the transmission without a mechanical clutch.
- Analogy: think of a torque converter like two fans (pump/impeller and turbine) facing each other in a bowl of oil. The engine spins the “pump” and moves oil; the moving oil turns the “turbine” which turns the transmission. Between them is the stator, a guide vane assembly with a one-way clutch that redirects fluid to multiply torque at low rpm (like a guide that redirects a water jet to push a wheel harder). Modern converters may also have a lock-up clutch that eliminates slip at cruise.
- Main functions: torque multiplication at low speed, smooth stall/engagement, and dampening torsional vibration.

Major torque converter components (what you will see and touch)
- Shell / housing / front cover: outer steel drum bolted to flexplate (flywheel). It forms the “bowl.”
- Impeller (pump): the part attached to the shell; fixed to the engine via flexplate; driven by the crank and forces ATF outward.
- Turbine: a finned hub inside the shell that is splined to the transmission input shaft; receives fluid energy and transmits torque to the transmission.
- Stator (reaction member): sits between pump and turbine on a one-way sprag/clutch; redirects fluid returning from turbine to the pump to boost torque during acceleration.
- Lock-up clutch (if fitted): friction plates inside the converter that can connect turbine to shell directly to eliminate slip at cruise.
- Hub and spline: turbine hub has splines that engage the transmission input shaft.
- Converter pilot/boss: the central boss or pilot that fits into the crankshaft pilot/bushing and centers the converter.
- Seals: the converter has sealing surfaces that seal against the transmission pump and input seal.
- Bolts: converter bolts through the torque converter shell to the flexplate/flywheel.

Why converters fail / symptoms that indicate replacement
- Symptoms:
- Severe slippage (engine revs rise but vessel speed not increasing).
- Shudder or judder under load or during lock-up (if equipped).
- Excessive internal noise (bearing/sprag noise).
- Transmission overheating, burnt ATF smell, dark burnt fluid.
- Metal particles in transmission pan or pan magnet, or heavy contamination.
- Visible cracks, damaged fins, or leakage at the seal.
- Causes:
- Overheating (loss of fluid cooling/contamination).
- Worn sprag/clutch in stator (reduces torque multiplication).
- Worn bearings or damaged fins—can cause imbalance.
- Lock‑up clutch failure (slipping plates).
- Foreign object damage or corrosion (marine environment).
- Front pump seal or input shaft damage on transmission.

Tools, equipment & parts checklist
- Service manual for your engine/transmission (required).
- Engine hoist and engine/transmission stands or shipboard supports.
- Transmission jack rated to the transmission weight.
- Torque wrench and appropriate sockets (impact wrench helpful for removal).
- Long extensions, breaker bar, universal joints.
- Screwdrivers, pry bars, drift punches.
- Seal puller, gasket scraper, cleaning rags, parts cleaner.
- New torque converter (exact model), new flexplate bolts if specified, threadlocker if called for.
- New transmission fluid (type and quantity per manual), new transmission filter and pan gasket.
- New pump seal / input seal / pilot bushing if warranted.
- Shop rags, drain pans, gloves, eye protection.
- Dial calipers/feeler gauges, inspection light, magnet for metal.
- Safety chain/slings for converter handling.
- Clean fluid source to pre-fill converter (if required by manufacturer).

Pre-removal inspection & prep
- Note: do not remove converter without planning how to handle the heavy assembly.
- Inspect area for corrosion, are mounts original, access obstructions.
- Label electrical connectors, sensors, cables, shift linkages and hose routings.
- Drain transmission fluid (or at least enough so that when you separate units there is minimal spillage).
- Remove prop shaft/coupling as needed to access transmission (follow ship-specific procedure).
- Remove engine-driven accessories only as required for access.
- Remove starter motor and any flywheel/flexplate access covers.
- Take photos for reassembly.

Step-by-step removal (general; follow manual for model-specific details)
1. Support engine and transmission:
- Secure the engine to prevent rotation. Use hoist/supports rated to hold the engine position while transmission is moved.
- Place a transmission jack under the transmission and raise it to take the weight.
2. Disconnect external connections:
- Remove electrical connectors to transmission sensors, neutral safety switch, and any ground straps.
- Disconnect shift linkage, speedometer cable/sensor, hydraulic lines, cooler lines (cap and plug lines to prevent contamination), and vacuum lines or vent hoses.
3. Remove bellhousing bolts:
- Loosen and remove bellhousing-to-engine bolts. Keep the engine supported; the bellhousing/transmission will separate once all bolts are removed.
4. Separate transmission from engine:
- Carefully slide the transmission back on the jack until the torque converter clears the flexplate face by a few inches so you can access converter bolts (the converter is still fully inside the bellhousing/splined on the input shaft until you pull it off).
5. Remove converter-to-flexplate bolts:
- Rotate engine (use starter or turn crank by socket) to access each converter bolt that threads through the flexplate into the converter front cover. Remove all bolts. Note: some bolts are accessible only by slightly turning the torque converter to align holes.
- Keep bolts organized in order and note threadlocker use if originally present.
6. Slide transmission/torque converter away:
- Support the converter as you slide the transmission farther back; the converter will slide off the crank pilot and then off the transmission input shaft splines. Pull the converter straight out from the transmission input—avoid tilting to prevent spline damage.
- If the converter is stuck to the input shaft, gently pry straight pulling at the converter hub flange areas using appropriate pullers or by letting the trans jack move back a little while keeping alignment—do not pry on the front pump area.
7. Remove converter from engine bay:
- Once free, lower and sling the converter for removal—it's heavy and may contain residual ATF.

Inspection of transmission and engine mating parts
- Inspect flexplate/flywheel:
- Check for cracks around bolt holes, heat spots, and ring gear condition. Replace if cracked or damaged.
- Inspect pilot bushing/pilot bearing:
- If worn, replace.
- Inspect crankshaft pilot seat for nicks or corrosion.
- Inspect transmission input shaft splines and front pump:
- Look for wear, gouges, scoring. Check pump vanes and front pump sealing surface for damage.
- Inspect transmission input seal:
- Consider replacing the input seal and front pump seal while the transmission is separated.
- Check bellhousing for cracks and alignment dowels for damage and presence.
- Check for metal contamination in the transmission pan and magnets; if heavy, internal transmission inspection/repair may be required.

Preparing the new converter
- Compare new converter to old: spline count, pilot diameter, bolt pattern.
- If required by the manufacturer, pre-fill the new converter with the correct ATF through the fill hole/standpipe until fluid visible at the inlet or per manual. Pre-filling helps prevent dry pump start and damage.
- Coat converter splines lightly with the correct transmission fluid—do not use grease.
- Make sure the converter is clean and balanced (factory-balanced new part).

Installation step-by-step
1. Rotate/position converter onto input shaft:
- Align converter pilot to the crank pilot. Push the converter onto the transmission input shaft, turning slightly as necessary until it bottoms fully onto the pump and you feel it seat. You should be able to feel/measure the converter engaging the front pump: typically you’ll push it until it drops forward slightly and then rotates about 1/4–1/2 turn to align bolt holes. The manual may specify the distance the converter must protrude from the bell housing before mating.
- Important: the converter must be fully seated—multiple full engagements of the splines are required so that the front pump is fully seated before the bellhousing is tightened. If not fully seated, bolts will bottom out in the flexplate and you will shear studs or bend the pump.
2. Confirm engagement:
- Reach into the bellhousing and try to rotate the converter gently. There should be smooth rotation; try to feel that the converter is seated on the torque converter pilot.
- Measure/verify the distance between the converter face and bellhousing per manual or ensure converter has engaged fully by feeling it contact the pump.
3. Mate transmission to engine:
- Using the transmission jack, bring the transmission forward slowly, aligning bellhousing to the engine block dowels. Guide the converter into the flexplate/flywheel opening; the converter should slip into position without forcing. If you meet resistance, do not force—back off and check alignment.
- As the transmission comes forward, check that the converter engages and that the flexplate holes align to converter bolt holes.
4. Install converter-to-flexplate bolts:
- Rotate the converter until a bolt hole aligns and install bolts finger tight. Install remaining bolts finger tight to pull converter into the flexplate.
- Once all bolts installed and hand-tight, torque them to manufacturer specification in a star pattern. Use new bolts if specified; use threadlocker if manual requires.
5. Install bellhousing bolts and torque:
- Tighten and torque the bellhousing-to-engine bolts to spec in the recommended sequence.
6. Reconnect all lines and linkages:
- Reattach cooler lines (proper clamps), shift linkages, electrical connectors, starter, and any removed components. Replace pan gasket and filter if removed.
7. Fill and prime:
- Fill the transmission with the correct type and amount of ATF. If you pre-filled the converter, fill to the “cold” level; exact procedure varies by model—follow Hino manual.
- Prime the converter if required by turning the engine (with starter engaged but not cranking long) to allow the transmission pump to pull fluid through. Some manuals call for cranking just enough for pressure build-up; others describe manual pump or pre-charging. Do not start the engine with no fluid pressure.
8. Initial start and bleed:
- Start engine and let idle. Move selector through each gear to work fluid through the converter and valve body (follow manufacturer warm-up/bleed procedure). Check for leaks, odd noises, and correct fluid level at operating temperature with prop or gearbox engaged/disengaged as specified.
- Recheck torque on converter bolts after initial run per manual (many manuals require re-torquing after a short run interval).
9. Sea trial / test:
- Conduct a slow sea trial under controlled conditions and check shifting, vibrations, temperatures, and any shudder. Recheck fluid level, bolts and leaks after cool-down.

Inspection checklist for common problems (what to look for)
- Fluid condition: brown/black and burnt smell = overheating; metal = internal wear.
- Metal flakes or heavy particles on pan magnets = major failure; inspect transmission internals.
- Converter runout/balance: if converter spins with wobble, do not install—replace.
- Front pump/seal damage: replace if groove/wear visible.
- Flexplate cracks: replace and check ring gear.
- Pilot/pilot bushing wear: replace if loose or scored.

Common installation mistakes and how to avoid them
- Not seating the converter fully: results in damage to input pump and broken bolts. Remedy: pre-seat converter fully; push until it bottoms and engage front pump fully before mating transmission.
- Not pre-filling or priming the converter: leads to dry start and pump damage. Remedy: pre-fill per manual.
- Reusing damaged bolts or wrong grade bolts: use correct spec bolts and threadlocker where required.
- Not replacing seals and filters when contamination present: leads to repeat failure.

After-replacement checks and run-in
- Re-torque bolts per manual after first hours of operation if required.
- Monitor transmission temperature; prevent overheating.
- Re-check fluid level when at operating temperature and during the first sea trial.
- Monitor for shudder, slip, or unusual noises for first 50 hours; change fluid sooner if contamination or burning smells appear.

When not to replace just the torque converter
- If the transmission front pump, planetaries, or internal components are badly contaminated with metal or the valve body is damaged, replacing only the converter may not fix the problem—transmission overhaul may be required.
- If flexplate or crank pilot is damaged, address those too.

Final notes (no guesswork)
- Exact torque values, fluid type, capacity, and any model-specific alignment procedures must come from the Hino W04D / W04C-T / W04C-TI Marine Workshop Manual. Use the manual for bolt torques, seal part numbers, and any special priming procedures.
- If you’re unsure at any step, get assistance from a technician experienced in marine transmissions; mistakes (improper seating, skipping seals, wrong fluid) cause expensive damage.

Concise troubleshooting quick list
- Slip + burnt fluid → overheated TC or lock-up clutch failure; replace TC, flush fluid, inspect pump.
- Shudder only at certain throttle → possible stator sprag or lock-up malfunction.
- Loud grinding or knocking → bearing or internal damage—inspect converter internals and transmission pump.
- Metal in pan → inspect for internal transmission damage; replacing only TC might not be enough.

That’s the complete beginner-friendly overview and step-by-step approach. Follow the Hino Marine Workshop manual for torque specs and model-specific details, take your time seating and priming the converter, and do thorough inspections during disassembly and after reassembly.
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