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

Procedure: Differential service — Isuzu N‑Series (NPR, NQR, NPS, NKR, NHR)
(Contains: routine gear oil change and full differential overhaul guidance. Where exact numeric specs are required (torque, capacities, backlash, preload, pinion depth) use the vehicle’s Workshop/Service Manual. I note typical ranges where appropriate.)

Safety first
- Work on level ground. Chock front wheels. Engage park and parking brake.
- Use a heavy-duty jack and rated jack stands under manufacturer‑specified lift points. Never rely on a jack alone.
- Wear safety glasses, chemical-resistant gloves, and protective clothing.
- Allow differential to cool if hot. Clean up spills immediately — used gear oil is hazardous waste; collect for proper disposal.
- Support axle/assembly adequately before removing components. Use proper lifting equipment for heavy parts (transmission jack / engine hoist).
- Disconnect negative battery terminal if doing electrical work nearby.

Tools and equipment
- Heavy-duty floor jack and rated jack stands
- Wheel chocks
- Socket set (metric), extensions, ratchet, breaker bar
- Torque wrench (1/2" up to 300 ft·lb and 3/8" up to 100 ft·lb)
- Impact wrench (helpful)
- Drain pan
- Fluid pump or suction gun for gear oil refill
- Seal puller
- Brass drift / soft hammer
- Pry bars
- Gasket scraper and cleaning solvent
- Wire brush, lint‑free rags
- Magnetic pickup tool
- Shop press (or suitable bearing driver)
- Bearing puller / slide hammer
- Punches, drivers and bearing race drivers
- Dial indicator with magnetic base (resolution 0.001" / 0.01 mm)
- Pinion depth tool / mandrel or OEM tool (for overhaul)
- Torque-angle gauge (if required by nut type)
- Bearing race installer and press adapters
- RTV or differential cover gasket (as required)
- Threadlocker (medium strength) and anti-seize compound
- New crush sleeve or pinion nut (if specified), new crush washer for drain plug
- New seals, bearings, ring & pinion set (if replacing)
- Shop manual / torque & spec data

Fluids and replacement parts (typical)
- API GL‑5 gear oil (Isuzu typically: SAE 80W‑90; many later models allow 75W‑90 synthetic — check manual). Limited slip differential requires correct friction modifier.
- Differential gasket or RTV sealant
- Drain plug crush washer (new)
- Pinion seal(s), axle seals as needed
- Bearings/pinion bearing kit (inner & outer) and races (if servicing bearings)
- Ring gear bolts (replace if torque‑to‑yield type) and new lock washers if specified
- Ring & pinion set if damaged
- Carrier shims if necessary

Routine differential fluid change — step‑by‑step
(Do this first for basic service; takes ~45–90 minutes)
1. Prepare: Park on level surface, chock wheels, raise vehicle and support on jack stands. Remove any splash shields required for access.
2. Clean area around fill and drain plugs to prevent contamination.
3. Place drain pan under differential.
4. Remove the fill plug first (important). Then remove drain plug and allow fluid to drain completely. If drain plug is magnetic, clean metal particles thoroughly.
- Tool use: socket to break loose drain plug; use hand ratchet to remove.
5. Inspect drained oil for metal flakes, slurry or coolant (if final drive cooled). Significant metal indicates internal damage — stop and plan for overhaul.
6. Clean and reinstall drain plug with new crush washer. Torque to factory spec. (If manual not available, snug to manufacturer guidance — do not over‑torque.)
- Tool: torque wrench set to specified drain plug torque.
7. Refill via fill hole using a fluid pump until oil level is at the bottom of the fill hole. On many Isuzu N‑series differential housings, fill hole is in side of housing; fill until it just starts to weep.
- Tool: suction pump or gear oil pump; measure volume as you add if you need to confirm capacity.
8. Install and torque fill plug to spec. Clean up spills.
9. Lower vehicle, test drive, recheck for leaks.

Common mistakes in routine service
- Removing drain plug before fill plug (causes slow/partial drain or cannot check level).
- Not cleaning magnetic plug debris; that can mask bearing failure.
- Overfilling or underfilling: both cause problems.
- Using the wrong gear oil (wrong API/viscosity or missing friction modifier for limited slip).

Full differential overhaul / ring & pinion service — step‑by‑step (advanced)
Required when gears or bearings are noisy, damaged, or when replacing ring & pinion. Only for experienced technicians with right tools. Follow workshop manual exactly for torque, shim thickness and pinion depth.

Preparation
- Remove drive shaft at universal joint or flange.
- Support differential housing and/or axle assembly as needed.
- Clean exterior and drain fluid (remove cover or drain plug).

Disassembly
1. Remove differential cover (or remove entire axle housing depending on design).
- Tool: sockets, pry gently to break seal after removing bolts.
2. Mark bearing cap location/orientation and the carrier orientation before removal (very important). Do not mix caps or rotate them.
3. Remove bearing caps and carrier assembly. Be prepared for heavy carrier removal.
4. Pull out axle shafts if needed to inspect seals or replace side bearings.
5. With carrier out, inspect ring gear and pinion gear. If replacing ring & pinion, unbolt ring gear from carrier (replace bolts if torque‑to‑yield).

Pinion removal and bearing removal
6. Mark fit and note crush sleeve or shim stack configuration before removal.
7. Remove pinion nut (may be captive). Use a breaker bar/impact. If crush sleeve is used, it will be destroyed upon removal — replace with new crush sleeve or new pinion nut as required.
8. Use bearing puller/slide hammer to remove pinion flange and outer bearing. Press the inner bearing/race out.
- Tool: slide hammer or press; remove races with driver/press.
9. Clean pinion bore and case thoroughly.

Pinion installation and preload
10. Install new pinion races (heat housing or press races in squarely). Use proper driver.
11. Install pinion bearings (inner then outer).
12. Set pinion depth to exact specification using pinion depth tool/mandrel and appropriate shim stack or shim collar.
- Tool use: pinion depth tool helps set the ring gear centerline relation to pinion. Measure and adjust shim accordingly.
13. Install pinion with new crush sleeve or tighten to required preload procedure (if adjustable – follow manual). Pinion bearing preload must be within the specified inch‑pounds / Nm or torque‑to‑turn target.
- Tool use: inch‑pound torque wrench (measured rotation torque) or specified torque plus angle per manual. If crush sleeve method: tighten to stretch and then back off as manual directs; many modern applications require a new crush sleeve each time.
14. Install new pinion seal.

Carrier preparation and ring gear
15. If ring gear is reused or replaced, ensure ring gear runout and clean mounting surfaces. Torque ring gear bolts to spec using proper sequence and threadlocker as required.
16. Install carrier with bearings and target shim thickness for initial backlash.

Backlash and bearing preload adjustment
17. Install carrier with bearing caps in original orientation, torque caps to spec.
18. Using dial indicator, measure ring gear backlash at multiple points (3‑12 o’clock positions) and average. Adjust lateral shims on carrier until backlash is within spec.
- Tool use: dial indicator mounted to housing, measuring ring tooth to pinion tooth movement. Adjust shims to increase/decrease backlash.
19. Check contact pattern by applying marking compound (Prussian blue or gear marking compound) on ring gear drive teeth, rotate pinion and observe contact pattern. Adjust pinion depth and/or carrier shims until pattern is centered on tooth face (pinion depth affects pattern position; backlash affects pattern concentricity).
- Tool use: gear marking paste, rotate ring/pinion under torque (use breaker bar on pinion nut or apply drive torque through wheels).
20. When pattern and backlash are correct, set final carrier bearing preload. This is done by shimming or tightening cap nuts per manual. Torque all fasteners to specified values with threadlocker where required.
21. Recheck backlash and pattern after final torque. Re‑adjust if necessary.

Final assembly
22. Install new differential cover gasket or apply RTV sealant and torque cover bolts to spec.
23. Refit drive shaft and any removed components.
24. Refill differential through fill hole with correct type and quantity of gear oil to bottom of fill plug.
25. Road test under load; recheck for leaks and recheck gear noise and temperature.

How each special tool is used (concise)
- Dial indicator: mounted to housing, tip against ring gear tooth; rotate ring to measure backlash — adjust shims until dial indicates target movement.
- Pinion depth tool / mandrel: fits pinion bore and is used to measure relative position of pinion tooth to ring gear root; transfers to shim thickness selection.
- Bearing puller & press: used to remove/install bearings and races without damaging components.
- Torque wrench: used on cover bolts, drain/fill plugs, ring gear bolts, and bearing caps. Follow exact torque values.
- Fluid pump: used to pump gear oil into fill hole cleanly; measure quantity if required.

Common pitfalls and how to avoid them
- Not removing fill plug first (prevents proper draining).
- Reusing crushed crush sleeve or pinion nut (replace as required).
- Mixing gear oil types or leaving out limited‑slip friction modifier — causes chatter and wear.
- Poor cleanliness — dirt in differential ruins bearings quickly. Keep everything spotless.
- Not marking bearing caps/orientation — reassembly with caps swapped destroys bearing alignment.
- Over/under torquing bolts — always use a calibrated torque wrench and the OEM values.
- Incorrect pinion depth/backlash — results in noisy gears and accelerated wear. Use pinion depth tool and dial indicator; verify with gear marking compound.
- Reusing old seals and gaskets — always replace.
- Driving immediately without settling: after filling, let vehicle sit briefly then recheck level.

Replacement parts checklist (recommended)
- Gear oil (correct grade and quantity)
- Drain plug crush washer
- Pinion seal and axle seals (as necessary)
- Bearing set if noisy / old (pinion bearings, carrier bearings)
- Bearing races (recommended to replace with bearings)
- Crush sleeve or new pinion nut (as required)
- Ring & pinion set (if damaged)
- Ring gear bolts (replace if specified) and lock washers
- Cover gasket or RTV
- Friction modifier (for limited‑slip)

Final notes (no fluff)
- Exact torque values, backlash range, pinion depth and fluid capacity differ by model year and axle variant — always reference the Isuzu N‑Series Workshop / Service Manual for your exact vehicle identification (VIN) and axle code.
- If you’re not comfortable with bearing preload, pinion depth and backlash setup, get a shop equipped for gear setup — incorrect setup destroys a new ring & pinion quickly.

Done.
rteeqp73

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