Short answer up front: replacing the shift forks on a D22 (Frontier/Navara/Hardbody/Terrano) requires removing the transmission, splitting the case, removing the selector rails and forks, replacing worn forks (and usually seals/bearings/syncros), then reassembling with correct clearances and torque. Below is a detailed, beginner-friendly, step-by-step guide including why it’s needed, how the system works, what can go wrong, required tools/parts, and safety notes.

1) Why this repair is needed (theory, simple)
- What a shift fork does: imagine the gearbox as a bookshelf of gears and the shift collars (sliders) as little sliding doors that lock a gear to the output shaft. The shift forks are the “fingers” that push those sliding doors back and forth along rails to engage a gear. If a fork is bent or the fork “toe” is worn, it can’t move the collar cleanly — the result is hard shifting, false neutrals, gears popping out, grinding, or inability to select gears.
- How the system works (short): the shifter in the cabin moves the shift lever → linkage → selector drum/rods/rails → forks. Forks sit on rails and engage the groove on syncro collars. Synchronizers match speeds and the forks slide collars to lock a gear to the shaft.
- When forks fail: physical wear at the fork contact points (notches), bent forks from impact/abuse, or rails/slot wear allow play. Worn forks let collars miss the gear teeth or slip out; bent forks can jam; excessive wear causes misalignment and destroyed synchronizers/gear teeth.

2) Symptoms that point to bad shift forks
- Gear slips out (especially under load)
- Gear pops out to neutral while driving
- Very loose or sloppy shifter with play left-right or in/out on gear selections
- Grinding when changing gears and/or inability to select a gear without double-clutching
- Uneven wear pattern on synchros (if you inspect)
- Metal filings in transmission fluid

3) Components you will handle (every component described)
- Transmission case (two halves): houses shafts, gears, bearings. Split to access internals.
- Input shaft: carries engine torque into the gearbox, supports gears and synchronizers.
- Main/output shaft (counter or layshaft depending on gearbox design): carries gearsets to final drive.
- Gears (1st–5th, reverse): the toothed wheels that provide gear ratios.
- Synchronizer (synchro) assemblies: friction ring + hub + sleeve (collar). They match speeds before locking the gear.
- Shift collars / sliding sleeves: the sleeves you move to lock a gear to the shaft.
- Shift forks (usually 3): the metal forks that slide the collars. Each fork has a contact pad and a “toe” that engages the collar slot.
- Shift rails/selector shafts: the shafts the forks ride on; they translate linkage movement into fork motion.
- Selector drum/shafts/detents: the mechanism providing positions for each gear; detent balls/springs hold rails in place.
- Snap rings / circlips: hold shafts and hubs in position.
- Bearings (roller / needle / ball bearings): support shafts and maintain axial/radial position.
- Seals / gaskets / O-rings: keep gear oil inside.
- Shift lever/linkage components and bushings: connect cabin shifter to transmission selector.
- Transmission mounts / crossmember: support the trans under the vehicle.

Analogy: Forks = your fingers, collars = the bookends you slide to hold a book (gear) in place, rails = the rails your fingers slide along, synchronizers = your hand slowing the book down before you clamp it.

4) Tools & special tools
- Tools: complete metric socket set (6mm–22mm), torque wrench, ratchet, breaker bar, extensions, Allen keys, flat and Phillips screwdrivers, pliers, snap-ring pliers, hammer and brass drift, punch set, pry bars, wire brush, drain pan, rags.
- Lifting/support: quality jack, jackstands, transmission jack or large floor jack + wood block, engine support or engine hoist (if needed).
- Specialty: circlip pliers, bearing puller, press (for bearings), seal driver, dial indicator (for backlash/endplay measurement), feeler gauges, grease, RTV gasket or new case gasket (if required).
- Safety PPE: gloves, eye protection.

5) Parts to buy before starting
- Replacement shift fork(s) (OEM or OEM-equivalent)
- New case gaskets/sealant, output shaft seal(s), input seal(s)
- New shift rail bushings/detents if worn
- Synchronizer rings (if worn) — commonly replaced when forks fail
- Bearings if wear is found
- All relevant snap rings, small parts, and transmission fluid (correct spec)
- New trans mount(s) if old

6) High-level procedure (step-by-step for a beginner)
Note: This is a full gearbox rebuild-style job. Don’t rush. Work in a clean space, bag and tag bolts, photograph subassemblies before removal.

A. Preparation & safety
- Park on level ground, chock wheels. Disconnect negative battery terminal.
- Lift vehicle safely on jackstands or use lift. Support the engine if removing bellhousing bolts leaves engine unsupported.
- Drain gearbox oil into pan; dispose properly.
- Remove center console or trim to disconnect/unscrew shifter assembly from inside (this prevents damage and frees linkage).
- Remove driveshafts: for 4x4 you’ll remove driveline/prop shaft(s); for front-wheel drive variants remove CV axles or half-shafts as required. Mark alignment for reassembly.
- Remove starter and any wiring harnesses on bellhousing.
- Remove clutch slave cylinder or disconnect linkage (do not remove clutch cylinder unless required — support it out of the way).
- Remove crossmember/trans mount bolts; support trans with transmission jack.
- Unbolt bellhousing from engine (crank positioning may help); lower transmission.

B. On the bench — external disassembly
- Clean exterior to prevent debris entering case.
- Remove top cover (if serviceable) and shift lever mechanism.
- Remove any external selector mechanisms and shift linkage from the trans.

C. Split the case
- Unbolt case halves in sequence (mark halves and orientation). Use appropriate procedures shown in service manual; the halves may be tight — use gentle tapping.
- Note gearbox internals’ relative positions and the order of gears, shims, and spacers. Photograph every step.

D. Remove selector rails, forks, and collars
- Remove snap rings holding gears/hubs. Extract synchronizer assemblies carefully: note orientation.
- Remove shift forks: these slide off the rails. Label which fork corresponded to which gear position (usually 1/2, 3/4, and 5/R).
- Inspect rails and fork bores for wear. Check fork toe and friction pad surfaces.

E. Inspection — what to measure and look for
- Fork condition: look for cracks, bends, notches or heavy wear where they contact collar grooves. Light wear can cause shifting problems; replacement advised if any notch/burr/bend.
- Rails: check roundness and wear; galling causes binding. Replace if grooved.
- Synchronizers: check friction ring chamfers and notches. If rings show heavy wear or broken teeth, replace.
- Collars/sleeves: inspect for worn teeth, burrs, or mushrooming.
- Bearings: rotate and check for roughness. Replace any noisy/worn bearings.
- Gears: inspect teeth for chipped or rounded profiles.
- Snap rings and circlips: replace any that are deformed.
- Measure endplay/backlash (dial indicator) per service manual. Excessive backlash means other components (bearings, shims) need replacement.

F. Replace parts
- Install new shift forks and any bushings/bearings/syncros you decided to replace. If you replace bearings, press them on using a press or appropriate driver.
- If a fork is bent: replace - do not attempt to hammer it straight as hardness and geometry will be ruined.

G. Reassembly basics
- Clean all mating surfaces. Install new seals with drivers and shims in correct order.
- Reinstall synchronizer hubs and collars, ensuring correct orientation and all snap rings are seated.
- Slide forks on rails making sure each fork engages the correct collar slot; move the selector to confirm smooth movement.
- Use correct detent balls/springs in their positions.
- Torque case bolts to factory specs (see notes below) in required pattern. Use sealant where required by manual.
- Reinstall external selector mechanisms and shifter assembly.
- Reinstall transmission in vehicle: align bellhousing to engine, torque bolts to spec, reconnect mounts, driveline, wiring, starter, clutch slave as necessary.
- Refill with specified transmission fluid and bleed clutch (if needed).

H. Testing & break-in
- Before driving, with engine off, shift through all gears to check smoothness and no binding.
- Start engine, with vehicle safely on jackstands (wheels free), test each gear under load at low revs.
- Road test slowly first; listen for unusual noises. Re-check fluid level after warm-up and after initial test drive.

7) Torque specs & precise measurements
- Exact torque specs, backlash and endplay values vary by model/year and are critical. Use the Nissan factory service manual or a reputable shop manual for the D22 to get:
- Bellhousing bolts torque
- Case bolts torque sequence and values
- Main bearing preload / endplay values, and gear backlash tolerances
- If you don’t have the manual, download or print the specific procedure before starting. Incorrect torque or shim assembly can destroy the gearbox.

8) Common mistakes and what can go wrong (so you avoid it)
- Not cleaning and labeling: losing orientation of forks/collars leads to bad reassembly and hard shifting.
- Reusing worn detents/dogs/snap rings: may cause disassembly or pop-outs.
- Not replacing seals/case gaskets: leads to leaks.
- Forcing parts: pressing or hammering without correct tools damages shafts, forks, or bearings.
- Incorrect shimming/backlash: causes premature gear or bearing failure; noisy operation.
- Reinstalling rails incorrectly: forks must be in correct slots; otherwise selectors won’t align to gear positions.
- Not checking rails for wear: new forks on bad rails still slip and wear quickly.
- Incorrect fluid type or level: leads to gear wear and overheating.
- Bent forks: sometimes a sign of a deeper problem (e.g., broken gear teeth, hardened syncro problems, or a slammed shift); simply replacing forks without checking cause can let the new forks fail.

9) When to consider a professional
- You don’t have a transmission jack, press, or dial indicator.
- You find bearing damage or complex shim adjustments required.
- You find significant gear or hub damage (rebuilding beyond forks).
- You can’t get exact service manual specs.

10) Final checklist before you call it done
- All bolts torqued to spec and in the right sequence.
- New seals installed and no gaps in case mating surfaces.
- Forks move smoothly and collars fully engage gears.
- Correct fluid type and correct level.
- Shift linkage adjusted per manual, detent function confirmed.
- Test drive and recheck fluid and fasteners.

Safety reminders (brief)
- Always support the vehicle and transmission properly. Never work under a car supported only by a jack.
- Wear eye protection and gloves. Keep limbs and clothing away from moving parts during tests.

If you follow these steps methodically, label everything, and replace not only the fork but any worn mating parts (rails, syncros, bearings, seals), you’ll restore reliable shifting. For exact torque values, shim thickness, backlash, and endplay figures, consult the D22 factory service manual before tightening fasteners.
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Nissan Navara D22 Engine ZD30 Turbo stock : 1741 Nissan Navara D22 Engine ZD30 Turbo stock : 1741.

Installing Tough Dog Torsion Bars for Nissan Navara D22 Heavy duty 4WD Tough Dog torsion bars dramatically increase ride-quality and control as well as restore the spring rate lost via ...

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