Hino Profia F20C Dump Truck Oil Pressure Indication Troubleshooting The Pressure Indication Light comes "ON" everytime the RPM reaches 500 above and the analog pressure indicator is also not ...
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- Safety and preparation
- Disconnect battery: prevent starter motor engagement and electrical short. Remove negative terminal first. Use insulated wrench.
- Stabilize vehicle: chock wheels, set parking brake, work on flat level ground. Use heavy-duty jack stands rated for the truck’s weight — never rely on a jack alone.
- Personal protective equipment: impact-rated goggles, gloves, hearing protection, steel-toe boots.
- Service manual: obtain the Hino Super F Series GH1H workshop manual before starting — it contains model-specific torque values, bolt sequences, clearances and special procedures. Do not guess torque values.
- Overview of the job (what “flywheel” work usually involves)
- Removing gearbox/transmission to access flywheel.
- Removing clutch assembly (pressure plate and friction disc).
- Removing flywheel, inspecting or resurfacing/replacing it.
- Replacing associated items commonly replaced when the flywheel is out: flywheel bolts, pilot bearing/bushing, rear main seal, clutch disc and pressure plate.
- Reinstalling flywheel with correct torque and pattern, installing clutch with alignment, reinstalling transmission and testing.
- Tools you likely already have (basic tools) and how to use them
- Socket set (metric) with ratchet and extensions
- What it is: sockets sized to fit bolts and nuts; ratchet to turn sockets. Extensions reach recessed bolts.
- How to use: pick correct socket size, attach to ratchet, place squarely on bolt head; use steady force, pull on ratchet handle, avoid sudden jerk. Use breaker bar for initial break loose if stuck.
- Combination wrenches (metric)
- What it is: open-end and box-end wrench in one piece for tight spaces.
- How to use: use box end for higher torque, open end for quick turn; fit snugly to avoid rounding bolts.
- Breaker bar
- What it is: long non-ratcheting handle for loosening tight bolts.
- How to use: attach socket, steady two-handed force; watch for sudden release.
- Torque wrench (click-type, appropriate range)
- What it is: wrench that applies specified torque and clicks when reached.
- How to use: set required torque, tighten bolt until wrench clicks; always use correct torque and sequence. Use higher-range torque wrench or torque multiplier for heavy truck fasteners if needed.
- Hammer and dead-blow hammer
- What they are: metal hammer and rubber/plastic dead-blow.
- How to use: use dead-blow for persuading components without damaging mating surfaces; use metal hammer cautiously for stubborn parts.
- Screwdrivers and pry bars
- What they are: flat and Phillips screwdrivers; pry bars for levering parts.
- How to use: use to separate components, careful not to damage sealing surfaces.
- Pliers and snap ring pliers
- What they are: gripping tools; snap ring pliers remove/install circlips.
- How to use: select correct size, keep firm grip, release slowly.
- Wire brush / emery cloth
- What they are: cleaning tools for mating surfaces.
- How to use: clean bolt threads and surfaces before reassembly.
- Additional and special tools you will need (why required and how to use them)
- Transmission jack or heavy-duty floor jack with adapter
- Why required: safely lowers and raises the transmission during removal/installation; transmission is heavy and awkward.
- How to use: position under transmission, secure load with straps or blocks, lower slowly and controlled. Do not use a general hydraulic jack alone—use a transmission jack or two-person lift.
- Engine support bar or engine hoist / chain and load-rated engine support
- Why required: when the gearbox is removed the engine/transmission interface needs support to prevent engine sag or damage to mounts.
- How to use: support load over the engine with proper lifting points per manual; take load off mounts as directed.
- Flywheel holding tool (flywheel lock)
- Why required: to prevent flywheel/crankshaft from turning when loosening/tightening flywheel bolts.
- How to use: engage tool into flywheel ring gear or bolt holes to lock the flywheel while breaking or applying torque; ensure solid fit and do not damage ring gear teeth.
- High-capacity torque wrench or torque multiplier
- Why required: flywheel bolts on heavy truck engines often require very high torque beyond normal household torque wrenches.
- How to use: set to required torque or use torque multiplier per instructions; if using multiplier, follow sequence and re-torque as required.
- Pilot bearing/bushing puller and installer
- Why required: to remove and install the pilot bearing/bushing cleanly without damaging the crankshaft bore.
- How to use: follow puller instructions to extract the old bearing; use driver or installer tool sized to the new bearing to press it squarely into the crankshaft until flush.
- Flywheel puller or heavy-duty pry setup (if flywheel is tight)
- Why required: some flywheels can bind on the crank flange and need controlled axial pull to remove.
- How to use: attach puller to flywheel bolt holes, slowly and evenly extract flywheel. If using pry bars, apply even pressure around circumference; protect surfaces with wood/metal backing.
- Dial indicator (runout gauge) and magnetic base
- Why required: to check flywheel axial runout so clutch will not chatter or prematurely wear.
- How to use: mount indicator to stationary part, sweep indicator tip around flywheel face at clutch mounting diameter; compare readings to manual limits.
- Clutch alignment tool (pilot alignment tool)
- Why required: aligns clutch disc to pilot bushing/bearing so transmission input shaft slides into place.
- How to use: after installing pressure plate loosely, insert alignment tool through clutch disc into pilot bore; center disc, tighten pressure plate in sequence to specs, then remove tool before transmission installation.
- Rear main seal installer and driver
- Why required: to install rear crank seal smoothly and evenly without damage.
- How to use: use driver sized for the seal lip diameter, tap evenly until flush with crank housing.
- Thread locker (medium or specified)
- Why required: prevents bolts from loosening due to vibration (follow manual for where to use).
- How to use: apply small bead to bolt threads or mating surface as specified; avoid over application.
- Anti-seize compound
- Why required: on certain bolts or mating surfaces where future removal is expected or corrosion is likely.
- How to use: apply thin layer per manual on specified studs/bolts only.
- Inspection light and mirror
- Why required: to inspect mating surfaces and bolt holes for damage or debris.
- How to use: illuminate recesses and use mirror to view hidden areas.
- Step-by-step procedure (high level, in safe order) — follow service manual exactly for model-specific steps and torque values
- Prepare and secure truck: disconnect battery, chock wheels, loosen drivetrain fasteners that are accessible with truck supported.
- Remove components needed for transmission drop: drain fluids as needed, disconnect drive shaft(s), linkage, electrical connectors, starter motor, speedometer/tacho cables, air lines (if applicable), hydraulic/clutch slave cylinder disconnect if present (support fluid out), and any exhaust or cross-members obstructing removal.
- Support engine and transmission: use engine support/hoist and transmission jack. Remove engine/transmission mount bolts as required.
- Lower and remove transmission: carefully lower transmission straight back to clear input shaft; watch for wiring lines and ensure alignment to avoid damage.
- Remove clutch assembly: unbolt pressure plate in a criss-cross pattern gradually to relieve tension evenly; remove pressure plate and clutch disc. Inspect clutch disc for wear, friction lining thickness, and springs.
- Remove flywheel: use flywheel holding tool. Remove bolts in a criss-cross sequence gradually. Flywheel is heavy — have an assistant and support it as bolts are removed. Remove flywheel from crank.
- Inspect flywheel and related parts:
- Check for cracks, heat spots (blueing), hot spots, severe scoring, or warped surface. Use dial indicator to check runout.
- If minor glazing or scoring, resurfacing (machining) can be possible — must be within thickness and runout limits in manual.
- If cracks or heat damage, replace flywheel.
- Always replace flywheel bolts if bolts are single-use or show stretch/corrosion — many manufacturers require new bolts.
- Inspect pilot bearing/bushing and rear main seal — replace if worn, noisy, or leaking.
- Replace rear main seal if disturbed or leaking: install new seal with installer tool for even seating.
- Install pilot bearing/bushing: press new unit in squarely.
- Install flywheel:
- Clean mating surfaces, remove debris from bolt holes.
- Place flywheel on crank flange in correct orientation (match dowels or alignment marks).
- Use new flywheel bolts if required. Apply thread locker or anti-seize per manual.
- Hand-start bolts, then use flywheel holding tool and torque bolts in the recommended pattern and stages to specified torque. If bolts are torque-to-yield, replace with new and follow tightening procedure exactly.
- Check flywheel runout with dial indicator after installation: compare with manual tolerances. If out of spec, replace or resurface as recommended.
- Install clutch assembly:
- Use clutch alignment tool to center clutch disc on pilot bearing.
- Fit pressure plate and tighten bolts gradually in criss-cross pattern to specified torque.
- Replace release bearing/throw-out bearing if old or worn.
- Refit transmission:
- Use transmission jack to lift and align input shaft to clutch disc splines; use care to avoid damaging splines or clutch face.
- Bolt transmission to engine by hand first, then torque to spec. Reconnect mounts, linkages, electrical connectors, lines and starter.
- Refill fluids, reconnect battery, test for proper clutch engagement and absence of leaks. Road test carefully to verify no chatter or abnormal noises.
- Parts commonly replaced when doing flywheel/clutch work and why
- Flywheel
- Why replace: cracked, severely heat-damaged, out-of-spec thickness or runout beyond manual limits. Resurfacing is possible if within limits, but resurfacing reduces thickness and can shorten service life.
- What to get: OEM or equivalent heavy-duty replacement that matches model and crank flange.
- Flywheel bolts
- Why replace: often torque-to-yield or single-use bolts; they can stretch and lose clamping ability. Corroded or damaged threads must be replaced.
- What to get: new bolts to OEM specification (grade and length).
- Clutch disc (friction plate) and pressure plate (clutch kit)
- Why replace: wear, glazing, weakened springs, or whenever clutch is disturbed to ensure long life and proper engagement.
- What to get: complete clutch kit matched to engine/transmission (disc, pressure plate, release bearing).
- Release (throw-out) bearing
- Why replace: wear or noise; cheap insurance when transmission is removed.
- What to get: OEM or equivalent bearing for GH1H.
- Pilot bearing / bushing
- Why replace: worn bearings cause vibration and poor alignment of input shaft; cheap and critical.
- What to get: correct inner diameter and outer fit for crankshaft.
- Rear main seal
- Why replace: typically accessible when flywheel removed; leaking seals will contaminate clutch and cause oil on clutch disc.
- What to get: correct seal for crankcase model; use proper installer.
- Bellhousing gasket / transmission input shaft seal
- Why replace: if damaged during removal or to prevent future leaks.
- What to get: exact fit gasket/seal per manual.
- Inspection and measurement checks to perform
- Flywheel face for scores and heat spots; use straight edge to check flatness.
- Flywheel runout with dial indicator.
- Check clutch disc thickness and pressure plate spring force if possible.
- Inspect crankshaft flange and threads, clean bolt holes and chase threads if necessary with appropriate tap.
- Check transmission input shaft spline condition.
- Common pitfalls and cautions
- Do not reuse torque-to-yield bolts unless manual allows; they can fail.
- Do not overheat or damage clutch friction surfaces when working.
- Ensure pilot bearing/bushing is properly centered — misalignment will make transmission installation difficult and cause premature wear.
- Never work under a vehicle supported only by a jack. Use rated stands and proper jacking points.
- Follow tightening sequences and torque specs from the Hino manual — incorrect torque leads to failure or vibration.
- Final steps
- Double-check all fasteners, reconnect all electrical and hydraulic lines, refill and bleed clutch hydraulic if applicable.
- Test operation in a safe area: verify clutch engagement/disengagement, watch for leaks, listen for unusual noises.
- If vibration, noise, or slipping occurs, stop and re-inspect flywheel runout, clutch alignment, and bolt torque.
- Where to get parts and support
- Hino dealer parts department for OEM flywheel, bolts, clutch kit, seals, and bearings.
- Reputable heavy-duty parts supplier for aftermarket clutch kits and flywheels — ensure correct part numbers for GH1H.
- Machine shop for resurfacing flywheel only if within spec; provide manual thickness and runout limits.
- Summary of minimum additional purchases you will probably need
- Clutch kit (disc, pressure plate, release bearing)
- Pilot bearing/bushing
- Rear main seal
- New flywheel bolts (and possibly flywheel if damaged)
- Thread locker and anti-seize
- If you don’t own them already: transmission jack, flywheel holding tool, high-capacity torque wrench or torque multiplier, pilot bearing puller/installer, and seal driver.
- Final note
- Follow the Hino GH1H workshop manual for exact procedures, bolt sizes, torque values and safety instructions. If any step feels beyond your tools or comfort level (heavy lifting, alignment, high torques), get professional help.
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1) Confirm system identity and specs
- Action: read the under‑hood/service label and workshop manual to confirm refrigerant type (likely R‑134a on older Hino trucks) and the correct oil type/quantity and factory charge.
- Theory: correct refrigerant and lubricant are chemically specific. Using the wrong refrigerant or oil causes poor lubrication, loss of cooling, and compressor failure.
2) Preliminary inspection and diagnosis
- Action: visually inspect condenser, receiver/drier or accumulator, hoses, fittings, and the compressor. Check for oil stains/soot, bent fins, debris, and blocked airflow. Run the system and note symptoms (weak airflow, warm vents, cycling).
- Theory: poor cooling can be from low refrigerant, leaks, restriction (drier/expansion device), compressor failure, or air/ moisture/non‑condensables. Visual clues (oil streaks, dye) point to leaks; debris or bent fins reduce heat rejection and raise high‑side pressure.
3) Leak detection and quantify charge status
- Action: use an electronic sniffer, UV dye plus lamp, or soap solution at joints. Attach manifold gauges to low and high service ports and measure static and running pressures at ambient temperature.
- Theory: a leak is the most common cause of low charge. Gauges give dynamic information: static pressure should approximate saturation pressure for ambient temperature; low running low‑side and low compressor suction indicate undercharge. Non‑condensables show by abnormally high high‑side pressure with low low‑side pressure.
4) Recover existing refrigerant (if any) per regulation
- Action: connect a certified recovery machine and evacuate the existing refrigerant into a recovery cylinder. Do not vent to atmosphere.
- Theory: legal and environmental requirement. Also recovery allows you to work on a sealed, controlled system and to add fresh refrigerant/oil in known amounts.
5) Repair leaks and replace service components as required
- Action: replace any leaking hoses, seals, condenser, drier/receiver or accumulator, O‑rings, or defective compressor. Replace the receiver/drier or accumulator whenever system is opened. Lubricate new O‑rings with correct PAG oil.
- Theory: recharging a leaking system only provides a temporary fix. The drier/receiver contains desiccant that removes moisture; if it is saturated or disturbed, moisture remains and causes acid formation and compressor damage. Replacing it and repairing leaks restores system integrity and correct moisture control.
6) Add oil and dye as required
- Action: measure and add the OEM‑specified amount and grade of compressor oil (and UV dye if you will use it), accounting for oil retained in replaced components.
- Theory: the compressor needs the correct oil volume/type for lubrication. Too little oil increases wear; too much oil reduces heat transfer and cooling capacity. Dye helps future leak detection.
7) Evacuate to deep vacuum and leak‑test
- Action: connect a vacuum pump and pull the system down to a deep vacuum (target ~500 microns) and hold for 10–30 minutes. Observe for pressure rise.
- Theory: deep vacuum removes non‑condensables (air) and moisture. Moisture in the system reacts under compression to form acids and sludge and also freezes at the expansion device causing restriction. Holding the vacuum checks for gross leaks.
8) Charge with refrigerant by weight while monitoring gauges and temps
- Action: use a calibrated refrigerant scale and charge the specified mass of refrigerant. Typical workshop practice: start the engine, set A/C to max, and charge with refrigerant into the low‑side port as vapor while monitoring manifold gauges and evaporator outlet temperature. Add slowly and watch pressure behavior and compressor load.
- Theory: charging by weight ensures the correct refrigerant mass in the system to achieve designed heat transfer. Charging while running allows refrigerant to circulate and prevents overcharging. Gauge readings and inlet/outlet temperatures allow you to verify proper operating pressures and superheat/subcooling, indicating the expansion device is metering correctly.
9) Verify operating pressures and performance; set final charge by superheat/subcooling if required
- Action: measure low‑side and high‑side pressures at operating conditions and check evaporator inlet/outlet and vent air temperatures. If the manual specifies superheat or subcooling targets, adjust the charge to meet them.
- Theory: correct pressures and proper superheat/subcooling confirm the evaporator is receiving the correct refrigerant mass flow and the condenser is rejecting heat properly. Undercharge: low suction pressure, warm vents, and high superheat. Overcharge: high head pressure, possible liquid slugging, and reduced cooling. Proper superheat ensures the evaporator is dry at the outlet (protects compressor); proper subcooling ensures liquid charge is sufficient.
10) Final checks and documentation
- Action: run a road or bench test cycle, re‑inspect for leaks (sniffer or UV), check compressor clutch cycling and system current, record final charge weight and pressures.
- Theory: dynamic testing confirms the fix under real loads. Documenting the weight and readings gives a baseline and helps diagnose future issues.
How recharging fixes the fault (theory)
- Primary mechanism: refrigerant circulates through the evaporator, absorbs cabin heat while evaporating, is compressed, rejects heat at the condenser, and returns as liquid to repeat the cycle. If refrigerant mass is low (undercahrge), the evaporator receives insufficient boiling refrigerant, reducing its cooling capacity; the low‑side pressure drops, superheat increases, and vents are warm. Adding the correct refrigerant mass restores the designed enthalpy transfer in the evaporator and condenser, normalizes pressures, and restores cooling.
- Limitations: recharging only fixes faults caused by insufficient refrigerant or lost oil. It does not fix mechanical failures (failed compressor, blocked expansion device, collapsed hoses, severely restricted condenser, or electrical faults). If leaks, moisture, or wrong oil remain, the problem will recur or damage the system.
Safety and regulatory points (short)
- Never vent refrigerant. Use recovery equipment. Wear eye/hand protection. Use the correct refrigerant and oil grade and follow local environmental laws and workshop procedures.
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