Isuzu NPR NQR NPS NKR NHR N SERIES TRUCK Workshop Manual Digital Download

Tools & consumables needed
- Basic hand tools: metric socket/ratchet set (6–24 mm), combination wrenches, extension bars, breaker bar.
- Torque wrench (0–200 Nm range).
- Transmission jack or heavy-duty floor jack + assistant.
- Engine support bar or jack & wooden block (to support engine).
- Snap‑ring (circlip) pliers (internal & external).
- Punch set and drift pins, brass or plastic drift where needed.
- Dead blow or soft‑face hammer.
- Bearing puller / slide‑hammer (for stubborn bearings).
- Seal driver & appropriate sized sockets.
- Puller for gears/shafts (if needed).
- Feeler gauges, straight edge, and depth mic or vernier caliper.
- Clean rags, solvent/degreaser, gear oil pan.
- New gearbox oil (Isuzu specified grade), gasket sealant, threadlocker.
- Replacement parts: shift forks (OEM part numbers for your N‑series model), shift fork pads (if fitted), selector shafts/rods bushings, circlips/snap rings, bearings or oil seals as inspected, transmission gasket set, and new gear oil.
- Personal protective equipment: safety glasses, gloves, steel‑toe boots.
- Clean, labeled trays or magnetic bowls for fasteners.

Safety precautions (must do)
- Work on level ground. Chock wheels and put vehicle in park/1st with parking brake on.
- Disconnect negative battery terminal before starting.
- Support engine when removing transmission: do not let engine hang from mounts.
- Use proper jack stands and a transmission jack — transmission is heavy and awkward.
- Wear eye protection and keep clear of pinch points when lowering heavy components.
- Keep work area clean and parts organized to avoid contamination of bearings/synchros.

Overview of procedure
1) Preparations
- Park vehicle, chock wheels, disconnect negative battery.
- Raise vehicle on ramps or hoist; place on stands. Remove any undertrays or splash shields blocking access.
- Block front wheels and set parking brake.

2) Remove ancillary components and disconnect linkages
- Remove shift lever boot and disconnect external shift linkage at the transmission (note/link or mark linkage positions).
- Remove driveshaft/prop shaft: mark orientation relative to flanges, remove U‑bolt/bolt sets, set aside.
- Disconnect speedometer cable/sensor and electrical connectors on transmission (reverse lights, neutral switch).
- Disconnect starter motor if it interferes with bellhousing removal.
- Remove exhaust sections, crossmembers and/or transmission mounts as required to gain access.
- Support engine from above (engine support bar) or with a jack under oil pan via wood block.
- Remove transmission mount(s) and crossmember.

3) Separate transmission from engine
- Loosen and remove bellhousing bolts progressively in crisscross pattern. Support gearbox with transmission jack.
- Pull transmission rearward off input shaft; guide out carefully to avoid clutch/pressure plate interference. If clutch is bound, loosen bolts and keep pressure off clutch fork.

4) Drain gearbox (if not already) and remove gearbox cover
- Place drain pan; remove drain plug and then top cover if needed.
- Remove gearbox inspection/side covers, shift selector housing/cover and any external plates to access selector forks and selector shafts.

5) Internal disassembly to access shift forks
- With transmission on bench (jack under), remove any retaining circlips/bolts holding selector shafts/rods in place.
- Note and mark position/orientation of each selector rod, forks and synchronizer assemblies. Take photos or sketch.
- Remove selector shafts/rods by sliding them out; forks will pull free with them. If rods are tight, use pry carefully (avoid scoring).
- Remove shift forks from sliding gear assemblies. Forks typically have pins or are caged by selector rail arrangement — remove retaining pins/circlips first.
- Remove synchronizer hubs, collars and related snap rings as needed to access fork pads and pivot points. Keep track of shims/spacers and their order.

6) Inspect components & prepare replacement
- Inspect shift forks for wear at contact faces, bend, cracks and worn pads. Check fork pads for excessive wear or missing material. Replace fork pads and/or entire fork assembly as required (Isuzu recommends replacing worn forks—ditto pads).
- Inspect selector shaft bore bushings, selector rail for scoring, synchro sleeves, keys, springs, bearings and snap rings. Replace bushings and seals if worn.
- Replace any oil seals or bearings exposed during disassembly if play or roughness found. Common replacement items: shift fork pads, selector rod bushings, side seals, input/mainshaft bearings if noisy.
- Clean all parts thoroughly with solvent, dry, and lightly oil with clean gear oil when reassembling.

7) Installing new shift fork(s)
- If new forks come with pads, fit pads with recommended adhesive or pins as per OEM instructions. Ensure pad orientation matches old ones.
- Slide new forks onto selector shafts/rods in the same orientation as removed. Ensure forks engage synchronizer collars correctly (the "tongues" of the fork must seat in the groove of the sliding sleeve).
- Refit any retaining pins or circlips to hold forks to sliders. Use snap‑ring pliers; ensure rings are fully seated in grooves.
- Reinstall selector shafts/rods through forks. There may be an order to the shafts—follow your markings/photos. Use a soft hammer or drift to seat shafts, avoiding damage.
- Replace selector shaft bushings/sleeves if applicable. Press in new bushings with a seal driver or socket sized to bushing O.D.

8) Reassemble transmission internals
- Reinstall synchronizer hubs, collars, hub springs, keys and snap rings in original order/stacking. Use new snap rings if recommended.
- Verify free rotation of gears, smooth operation of forks moving selection positions, and correct engagement of all sliding sleeves.
- Apply correct amount of clean gear oil to bearings and synchros during assembly.

9) Refit covers and prepare for vehicle reinstallation
- Replace side cover gaskets or use proper RTV/sealant where required.
- Torque all cover and case bolts to OEM specs (consult Isuzu workshop manual for exact torques).
- Reinstall any sensors through covers and ensure new seals are fitted.
- Refill with correct type and amount of gear oil.

10) Reinstall transmission into vehicle
- Align transmission to engine using transmission jack; ensure input shaft engages splines without forcing. If clutch alignment required, use clutch alignment tool to center the disc before mating bellhousing.
- Tighten bellhousing bolts progressively to spec; reinstall mount(s) and crossmember.
- Reconnect drive shaft, exhaust pieces, wiring, speedometer cable/sensors, and any removed components.
- Reconnect shift linkage and adjust to correct free play/neutral position per manual.
- Reconnect battery.

11) Test & final adjustments
- With vehicle still on stands, start engine and check for abnormal noises when shifting through gears. Check for fluid leaks.
- Test drive at low speed, cycling through all gears and ensuring smooth engagement and no abnormal synchro noise.
- Recheck oil level after short drive and torque of external fasteners.

How the tools are used (short guide)
- Transmission jack: supports and lifts/lower gearbox safely; use straps to secure case.
- Snap‑ring pliers: remove/install circlips holding forks/pins; choose internal or external type per ring.
- Bearing puller / slide hammer: remove stuck bearings or sleeves without damaging shafts.
- Seal driver/socket: press new oil seals/bushings squarely into bores.
- Punch & drift: carefully drive out roll pins or alignment dowels; use brass/plastic for delicate surfaces.
- Torque wrench: torque bolts to manufacturer specification to avoid case distortion or leaks.
- Engine support bar / jack: prevents engine sag when bellhousing is removed.

Common pitfalls & how to avoid them
- Losing orientation/ordering of parts: mark shafts, take photos, or lay parts out in sequence. Shims or spacers are critical.
- Not supporting engine/transmission properly: can damage mounts, misalign input shaft — always support engine and use a proper transmission jack.
- Reusing worn fork pads or bushings: leads to repeat failure—replace pads/bushings when wear evident.
- Mixing fork orientation: forks are often specific to gear positions — fit exactly as removed.
- Forcing transmission on input shaft: if it won’t slide in, check pilot bearing, clutch release position and alignment; do not hammer bellhousing.
- Not replacing seals/bearings when disturbed: cheap parts that cause leaks or noise if neglected.
- Improper torque or uneven tightening of case/covers: leads to leaking or warped flanges — use correct sequence & torque.
- Contaminating synchros/bearings: keep everything clean and use only recommended clean gear oil for assembly lubrication.

Replacement parts typically required
- Shift fork(s) (OEM part numbers per model)
- Shift fork pads (if used)
- Selector shaft bushings/sleeves
- Circlips/snap rings and retaining pins
- Gasket/seal kit (side covers, output seals)
- Possibly bearings or synchro components if found worn during inspection
- New gear oil

Final note
- This is a general step‑by‑step for Isuzu N‑Series transmissions; model variations exist. Always cross‑reference the exact Isuzu workshop manual for the specific N‑series chassis (NPR, NQR, etc.) for torque values, special tool part numbers, exploded parts diagrams and any model‑specific steps. Following the manual avoids drivability and safety issues.

No further questions.
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Isuzu nqr npr auto box relearn reset Reset gearbox automatic.

Isuzu nqr npr auto box relearn reset Reset gearbox automatic.

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