Short summary
This is a complete, beginner-friendly guide to replacing the leaf springs on a Hino Super F Series (GH1H) — theory, every component explained, tools and consumables, step-by-step safe procedure, common faults and how to test/what to watch for. Read safety warnings and follow them exactly. Consult the Hino workshop manual for the vehicle-specific torque values and any model-specific steps.

Why leaf springs fail (theory — short)
- Leaf springs support vehicle weight, locate the axle, control axle fore/aft motion, and absorb bumps by flexing. Think of a leaf spring pack as a curved stack of metal plates that acts like a flexible I-beam. When the vehicle goes over bumps the stack bends and stores energy, then releases it to return the axle.
- Over time springs weaken (metal fatigue), corrode, the leaves separate or crack, or bushings wear. Worn springs sag, change ride height, overload other suspension parts, cause axle mis-position, uneven tire wear, and unsafe handling.
- Replacement restores ride height, corrects axle location, and returns intended suspension travel and damping.

Overview of every component (what it is and what it does)
- Leaf spring pack (main leaf + graduated leaves + overload leaves): multiple steel leaves stacked and clamped by a center bolt. The main leaf is the longest; shorter leaves share the load. The overload leaf is an extra short leaf that takes extra weight when heavily loaded.
- Center bolt (spring bolt): holds the leaves aligned like a spine. It does NOT carry full shear; the spring perch/clamp and U-bolts locate and clamp the pack to the axle.
- Spring eyes (front and rear eye): formed loops at each end of the longest leaf where the spring attaches to hangers or shackles.
- Bushings (rubber/urethane inside spring eyes): cushion the pivot and reduce wear/noise. They prevent metal-on-metal wear and reduce vibration transfer.
- Front hanger (fixed hanger): welded or bolted to the frame; the front spring eye pivots here.
- Shackle (rear shackle) and shackle bolt: shackle is a hinged link that allows the spring to change length as it flexes; shackle bolts clamp the shackle to spring eye/hanger.
- Rear hanger/frame bracket: attaches to chassis and receives shackle.
- U-bolts, nuts, and saddle/plate: clamp the spring pack to the axle seat (spring perch). U-bolts locate and secure axle to the springs.
- Spring perch / axle seat: the flat or radiused surface on the axle that the spring sits on.
- Axle cap/top plate / retainer plate: distributes clamp load from U-bolts over the spring.
- Equalizer (in tandem axle or Walking Beam systems): linkage between springs to balance load between axles.
- Shock absorbers and mounts (big effect on handling): control spring oscillation; usually removed or unbolted during spring replacement.
- Bump stops / bump rubbers: block excessive travel.
- Brake lines, ABS sensor wires, air lines: routed near springs and must be supported/checked.
- Grease fittings: used on some shackles/bolts (if present).

Tools and consumables
- Tools:
- Heavy-duty hydraulic jack(s) and axle stands rated for the truck weight (do not rely on jack alone).
- Axle support stands or adjustable screw jacks (rated).
- Socket set (impact and hand), breaker bar, extensions.
- Torque wrench capable for heavy torque ranges (up to several hundred Nm).
- Combination wrenches, pry bars, large hammer, dead-blow hammer.
- Punch/drift, chisel, and punch set.
- Impact gun (optional but helpful).
- C-clamps, ratchet straps or chain binders to keep pack compressed while handling.
- Penetrating oil (e.g., PB Blaster), wire brush.
- Heat source (propane torch) only if trained and safe (be careful near brake/air lines and fuel).
- Spring compressor straps or heavy webbing for safety.
- Bushing press or suitable driver and arbor (large sockets/pipe) for bushings.
- Measuring tape, feeler gauges, marker.
- Consumables:
- New leaf spring pack(s) and replacement bushings, new U-bolts, new nuts/lockwashers, shackle bolts if worn.
- Anti-seize or thread locker as specified by manual.
- Grease, penetrating oil.
- Paint or anti-rust coating.
- Safety gear: gloves, eye protection, steel-toe boots.

Safety first — absolute rules (read and follow)
- Never work under a vehicle supported only by a jack. Use rated jack stands or axle stands.
- The spring pack is under/holds stored energy. If something suddenly releases it can injure you. Use straps/chains to control the spring during removal and installation.
- Remove load on springs (empty cargo tanks, release suspension load) before attempting to unbolt components.
- Chock wheels and put the parking brake on. Block to prevent rolling.
- If bolts are rusted, use penetrating oil and heat carefully; watch brake lines and fuel lines.
- If you are not 100% confident, seek a commercial shop/qualified technician.

Preparation and inspection
1. Park on a level surface, chock wheels front and rear of the non-working axle(s).
2. Empty load (if a truck, unload cargo) so springs are in service condition but not overloaded.
3. Measure and record ride height (frame-to-axle measurement) and take photos/notes of current assembly and line routing.
4. Inspect: spring cracks, sag, worn bushings, cracked shackles, loose U-bolts, rust, damage to axle seat, worn equalizer, and shock condition. Replace other worn parts at same time.
5. Obtain new spring(s), bushings, new U-bolts, and appropriate hardware.

High-level procedure (single-axle leaf spring replacement)
Note: sequence varies for tandem axles or walking-beam. For tandem systems, support both axles and follow equalizer procedure per manual.

A. Support vehicle and unload spring
- Chock wheels and engage park brake.
- Raise chassis slightly with a heavy-duty jack to take most weight off springs, then place rated axle stands under frame near spring hangers/under chassis. Alternatively, support axle with jack stands under axle housing on either side of the spring perch.
- The safe method: support the axle with stands positioned so the U-bolts can be removed without letting the axle drop. Use additional straps to secure axle to frame if necessary.
- Slowly lower the jack so axle weight is taken on stands/supports. The spring should be under minimal tension but not fully unloaded unless procedure calls for it.

B. Remove components
1. Remove shock absorber(s) connected to the spring/axle if they obstruct access.
2. Support the spring pack with a strap or chain (around the pack) to prevent it dropping. Keep the strap in place during unbolting.
3. Loosen and remove the U-bolt nuts evenly — do not remove one side completely and let the axle spin/drop. Remove U-bolts and top plate once clamp is free.
4. Remove the center bolt (if accessible) that holds leaves together or leaves pack aligned.
5. Remove the shackle bolt (rear) and pivot or the front hanger pin (depending on which end is pinned and which end is shackled). Use PB and heat if seized — but protect lines and rubber.
6. On fixed-front-hanger designs you may have to drive out a taper pin or undo nuts on the hanger mounting. Keep track of washers and orientation.
7. With shackles/hangers free and U-bolts removed, lower the spring slightly and slide out the pack from under the axle seat. Use pry bars carefully; do not bend the new spring.

C. Inspect axle seat and related parts
- Clean the spring perch and axle seat, inspect for wear or cracks.
- Check for flatness; replace or repair perch if broken or heavily corroded.
- Inspect hangers and shackles; replace if bent or worn.
- Inspect brake lines/air lines/ABS sensor mounts; relocate or secure as necessary.

D. Bushing replacement (if replacing bushings)
- If new spring includes new bushings pre-installed, okay. Otherwise, press out old bushings using a hydraulic press or bushing driver. Drive in new bushings until seated flush. Grease inner sleeve if required.

E. Install new spring pack
1. Lay the new pack under the axle in the correct orientation (bow forward or rear as per OEM). Main leaf curvature should match original orientation.
2. Align center bolt and leaves. Make sure center bolt is correctly seated in the spring perch slot.
3. Attach front eye to front hanger or bolt in shackle pivot. Use new shackle bolts if required. Do not fully torque yet unless manual instructs.
4. Attach rear shackle to spring eye; leave bolts loose for alignment.
5. Reinstall top plate and new U-bolts, start nuts by hand. Torque sequence: tighten U-bolts evenly in stages to bring springs to seat but do not fully torque until axle is loaded to normal ride height (see below). This prevents preloading or distortion.
6. Reattach shock absorbers and any mounts removed.
7. Reconnect brake lines/ABS wires to original routing and check for clearance.

F. Lowering and final torquing
- Gradually raise the chassis or remove axle supports so the vehicle settles to normal ride height on its springs (do not use parking brake to settle). With the vehicle resting on its wheels at normal ride height torque the U-bolts, shackle bolts, and spring eye bolts to OEM torque values.
- Important: Many truck manufacturers require final torquing with vehicle loaded to normal operating load; follow Hino manual. If not possible, at minimum torque to manufacturer spec and re-torque after short mileage.
- Typical practice: torque U-bolts gradually and evenly in a star pattern. Replace nuts in service with new grade hardware.

G. Final checks and road test
1. Re-check clearances (brake lines, shocks, exhaust).
2. Grease fittings and apply anti-seize to threads as required.
3. Lower vehicle fully to ground, chock and remove stands.
4. Test drive at low speed to check ride, noise, and alignment. Listen for clunks or squeaks.
5. Re-torque U-bolts and shackles after initial 50–100 km (or manufacturer-specified distance). Re-inspect after 500 km.

What can go wrong and how to detect/fix
- Improper support: axle drops suddenly and crushes or injures — always use rated supports and straps.
- Broken or cracked spring: if a leaf breaks under load during disassembly, it can release energy — control with straps and remove carefully.
- Seized U-bolts or hanger pins: can shear if over-forced. Use penetrating oil, heat, and correct size tools. Replace any stretched or corroded U-bolts.
- Incorrect orientation of spring pack: install backwards and the curvature and overload leaf will be wrong — ride height and handling will be incorrect.
- Wrong or worn bushings: cause noise and premature wear. Replace bushings with OEM type and grease per spec.
- Under- or over-torqued U-bolts: under-torqued -> U-bolts can loosen and shift axle; over-torqued -> crush spring pack, deform axle seat, strip threads. Always use a calibrated torque wrench and OEM torque specs.
- Unequal springs (replace only one side): leads to a tilt and uneven load; replace springs in axle pairs (both sides) or full set for symmetry.
- Damaged spring perch or axle seat: failing to repair can cause spring to slip and lead to axle shift.
- Shock/air-brake line interference: can be pinched, cut, or overstressed if not re-routed — always check after assembly.

Maintenance notes and tips
- Always replace spring packs in axle pairs (left and right) to keep handling balanced.
- Replace U-bolts and shackle bolts when reassembling; they stretch and can corrode.
- Paint or coat new springs to reduce corrosion.
- Re-torque hardware after first 50–100 km and again after 500 km.
- Check shackle bushings and hangers at every service interval.
- If vehicle has air suspension, ensure no conflicting operations and follow OEM air bag deflate sequence before lifting.

Torsion, torque specs and the Hino GH1H specifics
- Do not rely on generic torque numbers for final safety-critical torques. The Hino Super F Series GH1H workshop manual contains model/year-specific torque values and any special procedures (e.g., final torque with vehicle loaded).
- If you do not have the manual, obtain it or ask a Hino dealer for torque specs for: U-bolts, shackle bolts, front spring eye nuts, equalizer bolts, and shock mounting bolts. Typical heavy truck components require high torque (hundreds of Nm), so correct values are essential.

Troubleshooting after replacement
- Sagging on one side: check spring orientation, bushings, shackle rotation, and whether correct spring pack was installed.
- Clunking or knocking: likely loose U-bolts, worn bushings, or misaligned shackles — re-torque and re-inspect.
- Pulling or poor tracking: inspect axle positioning and wheel alignment, tires, and check for unequal spring rates.
- Vibration or harsh ride: check shock absorber condition and spring seating.

Analogy to help remember
- Think of the axle and springs like a person carrying a pack: the leaf spring pack is the backpack’s frame supporting load; the shackles are the straps that change length as the person moves; the U-bolts are the belt that keeps the pack tightly against the person (axle). If the straps are worn or the frame sags, the jacket slides and the person’s gait is off — same for the truck.

Closing safety reminder
This is hands-on heavy-truck work. If any step seems beyond your tools, workplace safety, or skill level, have the job done by a professional. Wrong assembly can lead to catastrophic loss of vehicle control or injury.

No further questions as requested.
rteeqp73

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Ordered procedure with theory (covers automatic and manual transmissions; follow OEM spec for fluid type, capacities, bolt torques, and checks).

Preparation — theory and purpose
1. Gather OEM information: exact transmission model, fluid type/spec (ATF type or gear oil grade), fluid capacity, filter/ gasket part numbers, and torque specs. Theory: using correct fluid ensures the right viscosity, additives (anti-wear, friction modifiers, detergency) and hydraulic properties. Wrong fluid causes poor lubrication, shifting faults, clutch slip, or damage.

2. Tools, safety, environment: jackstands or lift, drain pan, clean rags, torque wrench, filter gasket kit, new fluid, scraper, magnet pick, PPE, proper disposal containers. Theory: safe, clean environment prevents contamination and injury; correct tightening prevents leaks and air ingestion.

Initial vehicle condition and warming — theory
3. Warm the transmission to operating temperature (drive until normal temperature reached or run engine until normal). Theory: warm fluid has lower viscosity and expands so more old fluid drains out; hydraulic systems at temp reflect real operating level and remove varnish/soot more easily.

Vehicle support and access
4. Securely raise and level vehicle on a lift or jackstands, chock wheels. Remove any skid plates or guards to access pan/drain/fill plugs. Theory: correct vehicle attitude (level) ensures accurate level checks; safe access prevents accidents.

Drain/Primary fluid removal (two common cases)

For manual transmissions (gearbox)
5M. Locate and remove the drain plug; let fluid drain fully. Remove the fill/level plug to allow free flow. Theory: gravity drain removes most old oil; opening fill plug prevents vacuum and speeds flow. Note: a simple drain removes most but not all oil trapped in housings and bearings.

For automatic transmissions
5A. Remove the transmission pan (or drain plug if equipped) and drain fluid into pan. Loosen pan bolts evenly; remove last bolts slowly to allow fluid to trickle out. Theory: pan removal exposes filter and valve body area. Simple pan drain removes fluid from pan and valve body circuits but not torque converter or cooler lines — typically 30–50% of total fluid. Full fill/flush requires additional steps.

Inspection and filter/service parts
6. Remove and inspect filter (or screen) and magnet(s). Replace filter (cartridge or internal) and pan gasket/seal per kit. Clean pan and scrape mating surfaces; inspect magnet for ferrous particles and note size/quantity. Theory: filter removes soft debris and contamination; magnets collect ferrous wear particles. Large steel chips indicate severe gear or bearing wear requiring deeper diagnosis or rebuild. Replacing filter restores correct hydraulic flow and prevents valve/servo clogging.

Cleaning and pan inspection
7. Clean pan, magnet, and mating surfaces. Inspect for clutch material (dark fibrous debris), burnt odor, or metallic flakes. Theory: burnt smell/black fluid indicates overheated or oxidized fluid and degraded friction properties. Fibrous material indicates clutch wear (automatic clutch packs) and will affect engagement and slip.

Reassembly — torque and sealing
8. Install new filter and new pan gasket (or sealant per manual). Hand-start bolts, then torque in a cross/star pattern to OEM torque. Theory: even torque prevents gasket extrusion, leaks, and air ingress. Uneven torque can warp pan and cause leaks.

Refill — theory and methods
9. Refill with specified fluid. For manual transmissions: fill until fluid begins to dribble out of the fill/level hole with vehicle level; reinstall fill plug and torque. For automatic transmissions: initial fill through dipstick or fill port to the recommended pre-run level. Theory: correct level is critical — too low = poor lubrication, overheating, clutch/servo damage; too high = foaming, aeration, heat build-up, erratic shifts.

If automatic and you only performed a pan drain: after reinstall, start engine, cycle through gears, and with engine at operating temperature, check level on dipstick/level procedure and top up to correct level. Many automatics require level check with engine idling in Park or Neutral and at specified temperature. Theory: cycling distributes fluid into torque converter and valve body; temperature-sensitive level accounts for thermal expansion and ensures correct operating fluid volume.

For a more complete fluid change (automatic)
10A. If replacing near 100% of fluid: perform converter/cooler line flush or use pump-exchange procedure — drain cooler lines by disconnecting return line and running pump to push old fluid out until new fluid appears, or use dedicated exchange machine. Theory: torque converter and cooler lines hold significant fluid volume; exchange removes oil that a pan drain leaves behind and restores additive balance and cooling capacity.

Bleed/air removal and leak check
11. Run engine, shift through all gears slowly, hold each gear to allow fluid circulation. With engine running and at temp, verify level per manual and check for leaks. Re-torque pan bolts if required. Theory: circulating fills hydraulic circuits and removes trapped air; air/foam reduces hydraulic pressure and causes delayed or hard shifts.

Final checks and road test
12. Test drive under normal load, monitor shift quality, noise, and temperature. Recheck level after cool-down or per manual. Theory: dynamic test verifies restored hydraulic function, cooling, and that worn components haven’t produced new symptoms.

How this repair fixes faults — theory linked to symptoms
- Contamination and varnish: Old, oxidized fluid contains acids, varnish, and sludge that impede valve movement and lubrication. Replacing fluid and filter restores clean hydraulic fluid, improving valve actuation and reducing friction/ wear.
- Loss of lubrication/viscosity breakdown: Heat and oxidation thin or thicken fluid and degrade additives. Fresh fluid restores proper viscosity and anti-wear additives, lowering friction and bearing/gear wear and reducing overheating.
- Slipping clutches/poor engagements (automatic): Burnt fluid loses friction characteristics needed for clutch pack engagement. New fluid and a new filter restore friction properties and hydraulic pressure for firmer, consistent shifts.
- Harsh or delayed shifting (automatic): Blocked filters or varnished valves reduce hydraulic flow/pressure. Cleaning pan, replacing filter, and fresh fluid free valve bodies and re-establish correct pressures.
- Overheating: Old fluid loses cooling capability. New fluid improves heat transfer and cooling, preventing thermal damage.
- Metal wear detection: Finding metal flakes/magnets with significant ferrous debris points to internal wear of gears/bearings/clutches. Fluid/filter change removes existing particles but if debris continues, further repair (rebuild) is required; the change allows you to monitor particle rate in future fluids.
- Leaks: Replacing gaskets and properly torquing bolts cures pan/plug leaks that allow ingress of air/dirt and fluid loss, both of which cause functional faults.

Limits and cautions — theory and risk management
- Pan-only drain on automatics removes limited percent of fluid; symptoms caused by degraded torque converter or contaminated cooler lines may not be fixed without a full exchange.
- Flushing with aggressive solvents can dislodge deposits that block valves — use manufacturer-approved procedures or mild exchange methods.
- Large metal shards or heavy clutch material require teardown. A change will not fix mechanical breakage.
- Always use the specified fluid, do not mix incompatible ATF or gear oils — additive chemistry and friction modifiers are critical to clutch/brake behavior in automatics and synchromesh in manuals.

Post-service monitoring
- Record fluid color, smell, magnet debris for baseline. Recheck level and leaks after 50–100 km and again after heavier use. For severe-duty trucks, change intervals may be shorter.

Summary checklist (ordered)
1. Get OEM specs (fluid, capacity, filter, torques).
2. Warm vehicle to temp.
3. Secure vehicle and access transmission.
4. Drain fluid (drain plug or pan).
5. Remove/replace filter and gasket; clean pan & magnets; inspect debris.
6. Reinstall pan/plug with OEM torque.
7. Refill per type (manual: to fill hole; automatic: initial fill).
8. Start, cycle gears, reach operating temp, check level and top-up to spec.
9. Road test, recheck for leaks and level.
10. Monitor debris and performance; plan further diagnostics if metal debris or persistent faults.

Done.
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