Role: experienced automotive technician. No yapping. Step-by-step overhaul of the gearbox (gear set) on a Mitsubishi Delica L300 (manual transmission) — tools, safety, how each tool is used, replacement parts required, and common pitfalls.

Summary prerequisites
- Factory Service Manual (FSM) for Delica L300 — mandatory for exact torque, clearances and shim thicknesses. Use FSM numbers — the values below are typical guidance only.
- Clean, well-lit workspace, bench and press.

Safety first
- Work on a flat surface. Chock wheels. Use a rated floor jack and quality jack stands or a transmission hoist.
- Disconnect battery.
- Allow gearbox to cool. Wear safety glasses, gloves, and nitrile gloves for solvent work.
- Use a face mask when using solvent or compressed air.
- Use lifting straps or transmission jack for removal — gearbox is heavy. Never rely solely on the jack.
- Keep solvents and rags away from ignition sources.
- Dispose of gear oil and contaminated parts per local regulations.

Required tools (typical)
- Basic hand tools: metric socket set (6–24 mm), combination wrenches, screwdrivers, pliers.
- Torque wrench (range covering low to ~200 N·m).
- Impact or breaker bar (for stubborn bolts).
- Transmission jack or engine support bar.
- Hydraulic or arbor press (for bearings and races).
- Bearing puller / gear puller.
- Snap-ring pliers (internal and external).
- Dial indicator with magnetic base (for backlash and endplay).
- Feeler gauges and thickness gauge.
- Micrometer and vernier caliper (measure shafts, gear widths).
- Dead-blow mallet, brass drift, soft-faced hammer.
- Seal driver / pvc tube set.
- Punches, picks, scrapers.
- Gear marking compound (Prussian blue or white marking compound).
- Threadlocker (medium strength), anti-seize.
- Cleaning supplies: brake cleaner, solvent, lint-free cloths.
- Plastic or metal trays to store fasteners and parts labeled.
- New gaskets / RTV as required.

Replacement parts recommended (overhaul)
- Full bearing set: input shaft, layshaft, countershaft, mainshaft bearings (and races if separate).
- All seals and O-rings (input/output shaft seals, extension housing).
- Synchronizer rings (all synchro cones).
- Synchronizer hub and sleeve if worn.
- Shift forks (replace if bent or worn at contact pads) and fork bushings.
- Selector shaft and detent springs/balls if worn.
- Thrust washers, shims, spacer washers as per FSM (replace if worn).
- Snap rings/circlips (do not reuse).
- Gasket set for gearbox halves and extension cover.
- Mainshaft nuts, lock washers (replace torque-to-yield hardware if specified).
- Pilot bearing/bushing (between crank and input shaft) — if transmission had to be removed, inspect/replace.
- Gear oil (GL-4 manual tranny oil, e.g., 75W-90 or factory spec).
- Optional: input shaft speed sensor seal, differential bearings if part of assembly.

Step-by-step overhaul procedure

A. Remove transmission from vehicle (outline)
1. Park, chock wheels, disconnect battery.
2. Drain gearbox oil: remove drain/stub plug and allow to drain into container.
3. Remove driveshaft/propshaft and/or CV axles as applicable. Label and mark orientation for reassembly.
4. Disconnect shift linkage, speedometer cable or sensor, reverse light switch wiring.
5. Support transmission with transmission jack. Remove crossmember/mounts and transmission-to-engine bolts.
6. Slide transmission back to disengage from input shaft pilot; lower transmission carefully.
Tool use: transmission jack + straps to cradle gearbox; use pry bar carefully between bellhousing and engine if stuck.

B. Split gearbox case and initial inspection
1. Clean exterior, then remove bellhousing bolts, then case bolts, loosen and separate gearbox halves. Note dowel pins and alignment. Tap gently with soft mallet to break seal.
2. Photograph/label component orientation and gear stacks before full disassembly.
3. Remove shift forks, selector rails, and detent components. Keep parts in order.
4. Remove mainshaft, layshaft/countershaft, and input shaft assemblies. Note bearing placement and spacers.
Tools: snap-ring pliers and pullers for circlips; puller and press for bearings.

C. Disassembly of gear set components
1. Remove synchro sleeves/hubs by removing securing circlips and sliding off. Remove syncronizer rings.
2. Remove gears from shafts using puller or press. Use brass drift to support and prevent damage. Note gear order and orientation.
3. Remove bearings from shafts using press or puller. Do not pry off races with a screwdriver (risk damage).
Tool details:
- Bearing puller: attach jaws behind bearing flange and tighten center bolt to press bearing from shaft.
- Arbor/hydraulic press: press bearings off/down by applying steady pressure, using appropriate receivers (drift and sleeve) to avoid shaft damage.
- Snap-ring pliers: remove internal rings that retain gears and hubs.

D. Clean and inspect
1. Clean all parts with solvent, blow dry with compressed air.
2. Inspect gears: check for chipped/rounded teeth, scoring, pitting, excessive wear on dog teeth and synchro cones.
3. Inspect synchro rings for grooves worn into brass — replace if ridges are rounded or if significant wear.
4. Inspect bearings: roughness, pitting, brinelling — replace all bearings if any doubt.
5. Inspect shafts: scoring, burrs on splines, runout. Measure gear face width, journal diameters and bearing bores with micrometer. Compare to FSM wear limits.
6. Inspect case bores for bearing seats and cracks.

E. Decide on parts to replace
- Replace all bearings and seals as a minimum in an overhaul.
- Replace synchro rings if wear/galling or > specified wear limit.
- Replace shift forks if contact pads show uneven wear or forks are bent.
- Replace mainshaft nuts and locking hardware as needed.
- Replace circlips, shims, and any parts flagged by FSM.

F. Reassembly — bearings, shafts and gear stacks
1. Install new bearings onto shafts using press. Heat bearings slightly (oil bath to ~60–80°C) to ease fit onto cold shafts if required. Use drive sleeves to press on the bearing race — press only on stationary race when installing on shaft to avoid damaging bearings.
Tool notes:
- Press: Use supporting blocks so pressure goes through bearing inner race onto shaft shoulder.
- Heat method: heat bearing with induction or oil bath; do NOT exceed ~120°C.
2. Reinstall gears in correct order and orientation. Install synchro rings with chamfers correctly oriented (small end toward cone). Fit hub and sleeve assemblies, secure with circlips.
3. Check axial positioning of gears against thrust washers and shims. Fit new thrust washers where applicable.
4. Install selector forks and rails; ensure forks engage hubs properly and slide smoothly.

G. Backlash, endplay and shim setting
1. Set pinion/backlash if differential inside case — if applicable. Use dial indicator on ring gear to measure backlash by rocking the gear under light load. Typical manual trans backlash ~0.10–0.20 mm (check FSM). Adjust shims to achieve correct backlash.
2. Measure mainshaft input endplay with dial indicator; adjust with specified shims or thrust washers to achieve correct endplay (FSM).
3. Check synchro engagement and sliding fit of hub and sleeves — they should shift smoothly with minimal free play.
Tool use:
- Dial indicator: mount solidly to case; zero on gear tooth; rotate gear and measure runout/backlash.
- Feeler gauges to check gaps as required.

H. Final assembly of the case and pre-install checks
1. Install new case gasket or apply RTV per FSM. Clean mating surfaces thoroughly.
2. Apply assembly lube to bearings and gear teeth before final assembly.
3. Torque case bolts in correct sequence to FSM torque values. Use threadlocker for specified bolts.
4. Reinstall external components: speedo sensor, selector linkage etc. Replace extension housing gasket/seal.

I. Installation back in vehicle
1. Lift transmission with jack, align input shaft with clutch/bearing, and slide forward evenly to engage pilot.
2. Torque trans-to-engine bolts to FSM values. Reinstall crossmember and mount, torque mounts.
3. Reconnect driveshaft(s), linkage, wiring. Refill with specified gear oil to fill level.
4. Reconnect battery. Test shift through gears with engine off, then run engine and test drive.

Important tool usage details and techniques
- Torque wrench: always use a calibrated torque wrench for critical fasteners (bellhousing, differential preload nuts). Use correct ranges and sequence in FSM.
- Press vs heat: press bearings off with arbor press. When installing, heat the bearing slightly to expand inner diameter for interference fit; do not apply heat to shafts. Press on inner race only when fitting a bearing to a shaft — pressing on outer race damages bearing.
- Dial indicator: zero on a stable reference, rotate assembly slowly to measure backlash/endplay. Record before/after adjustments.
- Gear marking compound: apply a thin film to a tooth and rotate the gear under light load to check contact pattern. It should be centered on gear face; incorrect pattern means shim adjustment needed.
- Snap rings: use proper snap-ring pliers to avoid bending. Replace snap rings rather than reusing.
- Cleanliness: contamination kills bearings — keep parts covered and use lint-free cloths.

Common pitfalls and how to avoid them
- Reusing worn bearings, synchros, or seals — replace them. Reuse is a frequent cause of short life.
- Incorrect shim placement: mark and bag shims in sequence during disassembly. Use micrometer and FSM tables to select shim thickness. Do not guess.
- Over-pressing bearings or pressing on wrong race — leads to bearing failure. Apply pressure only on the surface intended (inner race for shaft installation).
- Missing or misplacing circlips or thrust washers — always reinstall in the original orientation and location.
- Mixing parts from different gearsets — keep assemblies together. Do not swap halves without measuring clearances.
- Over-torquing or under-torquing case bolts — always use torque wrench and FSM sequence.
- Not checking backlash or gear contact pattern — causes noisy gears and premature wear.
- Not replacing detent springs/balls — causes sloppy shifting.
- Contaminating new bearings with dirt/old oil — clean bench and parts before assembly.
- Forgetting to replace input pilot bearing/bushing — can damage new input shaft bearings quickly.
- Using wrong oil (GL-5 vs GL-4) — GL-5 additives can harm yellow metals in synchronizers. Use GL-4 if specified.

Torque and clearance notes (advice)
- Exact torque values, shim thicknesses, and backlash/endplay specs vary by model and year — use the Delica L300 FSM for precise numbers. Typical backlash for manual gearboxes is ~0.10–0.20 mm; mainshaft endplay commonly 0.05–0.30 mm, but do not rely on these if not confirmed by FSM.

Final checks and break-in
- Rotate gearbox by hand to ensure smoothness and no binding.
- Fill with correct amount & type of gear oil.
- After installation do a low-speed test run and re-check for leaks, unusual noises and correct gear engagement.
- Re-torque external fasteners after first test drive per FSM.

If you need a concise checklist or a parts list with approximate part numbers for the L300, consult the FSM or OEM parts catalog for your engine/transmission code.
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Tools & supplies
- Basic hand tools: metric sockets and wrenches, extensions, breaker bar, ratchet
- Torque wrench (appropriate range)
- Screwdrivers, punches, drifts, hammer (soft-faced)
- Snap‑ring pliers (internal + external)
- Bearing/gear puller (3‑jaw)
- Hydraulic/arbor press (or strong bench vise)
- Dial indicator with magnetic base
- Feeler gauges, vernier calipers, micrometer
- Snap‑ring/retaining ring set
- Transmission jack or sturdy floor jack + gearbox support
- Engine support or jack under bellhousing if needed
- Clutch alignment tool
- Cleaning solvent, brushes, lint‑free rags, compressed air
- Rubber mallet, brass drift
- New gearbox oil, drain pan
- Seal driver set
- Threadlocker (medium), assembly lube
- Replacement parts (see list below)
- PPE: safety glasses, gloves, hearing protection

Typical replacement parts to have on hand
- Complete synchronizer ring (baulk/blocker) kit for each affected gear
- Hub and sleeve assemblies when worn/damaged
- Shift forks (if wear on contact surfaces), detent springs/balls
- Bearings (input/output/countershaft) and seals
- Mainshaft/or countershaft snap rings, thrust washers, shims
- Gasket/seal kit, new gearbox oil
- Any damaged gears or shafts if inspection finds scoring

Safety precautions (non‑negotiable)
- Park on level ground, chock wheels, disconnect negative battery terminal.
- Support vehicle securely on jack stands (never rely on a jack).
- Use a transmission jack to support gearbox when unbolting.
- Wear eye protection when using solvents, compressed air, or presses.
- Drain gearbox fluid before removal; catch and dispose properly.
- Be careful with heavy components (gearbox, shafts) — use two people or lift gear.
- Note orientation/sequence of parts, mark shafts before disassembly.

Step-by-step procedure

A. Vehicle prep & gearbox removal
1) Disconnect battery negative. Raise vehicle, chock wheels, place on stands.
2) Drain transmission oil.
3) Remove any components blocking access: center console/shifter assembly, heat shields, driveshaft(s) or CV axles (depends on configuration), speedometer cable/sensor, wiring connectors, starter motor, crossmember(s).
4) Support the engine or bellhousing if removing gearbox while engine is supported by engine mounts. Use engine support or a jack under oil pan with block.
5) Support gearbox with transmission jack. Unbolt gearbox from bellhousing and engine block (12/6/3 o’clock bolt pattern), remove clutch release mechanism/throwout bearing or concentric slave if necessary.
6) Lower gearbox carefully out of vehicle. Keep oriented and note shift lever position.

B. Disassembly of gearbox to access synchronizers
7) Secure gearbox in a clean workbench vise (soft jaws). Remove outer covers/inspection plates.
8) Remove shift rail assembly and top cover to free shift forks.
9) Remove snap rings retaining bearings/gears on main/countershaft. Use snap‑ring pliers and keep rings in order.
10) Use puller or arbor press to slide gears off shafts; press off bearings as needed. Use brass drift to tap out shafts if required.
11) Remove synchronizer hubs and sleeves: withdraw shift forks, slide off hub assemblies. Keep one section intact to track orientation.
12) Carefully remove blocker/baulk rings and any small springs or keys. Note orientation of tapered faces — they are directional.

How to use the specific tools correctly
- Snap‑ring pliers: select internal vs external, fit tips into ring eyes, squeeze gently to remove. Keep rings from springing out; trap under rag.
- Gear/bearing puller: seat jaws evenly, thread center bolt onto shaft end, tighten gradually with wrench while supporting shaft. Don’t scar shaft — use protective cap on center bolt.
- Arbor/hydraulic press: support component on correct adapter so pressing force is straight. Press bearings off slowly; use long support to avoid cocking. Use heat (hot oil bath or torch briefly) on gear (carefully) to aid removal if stuck.
- Dial indicator: mount magnetic base to solid housing, contact shaft end or gear shoulder, push/pull to measure endplay. Zero indicator, take readings per manual.
- Calipers/micrometer: measure thickness of synchronizer ring friction surface and compare to new or service limit.

C. Inspection & measurement
13) Inspect synchronizer (baulk) rings: check friction surface for glazing, heat spots, chipped teeth, or worn taper. Measure thickness at wear surface and compare to service limit. Replace if worn, cracked, or the radially stepped face has lost the taper.
14) Inspect hubs/sleeves: check for wear in splines, keyways, internal dogs. If sleeve dogs are rounded or hub grooves are worn, replace hub/sleeve assembly.
15) Inspect shift forks for wear at pad/contact area; if grooves exceed spec replace forks.
16) Inspect bearings for roughness or play. Replace all bearings that don’t roll smoothly.
17) Inspect shafts and gear teeth for burnout, scoring, or excess wear. Replace if necessary.
18) Check snap rings and thrust washers for wear and replace if deformed.

D. Replacement and reassembly
19) Clean all parts thoroughly; blow out oil galleries and dried residue. Use solvent and dry with compressed air.
20) Install new synchronizer rings in correct orientation. Note: tapered face of ring must face the hub/sleeve per OEM orientation (usually small diameter of taper toward gear; refer to ring marking or arrow).
21) If replacing hub/sleeve, press new bearings as required, fit hub onto mainshaft and secure with snap rings/thrust washers in the correct sequence. Use assembly lube on splines.
22) Refit gears onto shafts with proper spacing shims and thrust washers. Replace any shims removed only with factory thickness or measured equivalents. Do not reuse deformed circlips.
23) Set endplay: assemble shafts partially and measure axial endplay with dial indicator. Add/subtract shims as required until endplay matches service spec in manual. Typical spec often 0.05–0.3 mm but check manual.
24) Reinstall shift forks and rails. Ensure forks engage hub slots properly and move freely but no excessive play.
25) Torque all fasteners to OEM specs. Apply threadlocker where specified.

E. Bench check & final preparations
26) With gearbox assembled on bench, shift through all gears to ensure smooth engagement of hubs/sleeves and that synchronizers lock up correctly. If 1–2 wears, those gears should now synch smoothly.
27) Replace all external seals and gaskets. Install new drain and fill plugs with crush washers if applicable.
28) Refill with correct spec gearbox oil.

F. Reinstallation
29) Using transmission jack, raise gearbox into position, align with bellhousing, and slide onto pilot bearing/clutch input shaft. Use clutch alignment tool if reinstalling clutch. Start bolts by hand then torque to spec in pattern.
30) Reattach crossmember, driveshafts/CV axles, starter, shift linkage, wiring harnesses, and reconnect battery.
31) Lower vehicle, fill any fluids removed, and test shift operation with engine running in neutral. Check for leaks.
32) Road test: start with light shifts, then full operation. New synchros sometimes need a short break‑in.

Common pitfalls and how to avoid them
- Wrong orientation of synchronizer ring: always re‑install with correct taper facing hub/gear; wrong side causes poor synchronization.
- Reusing worn hub/sleeve: rings alone often won’t fix hard shifts if hub or sleeve dogs are worn — replace entire hub/sleeve assembly when in doubt.
- Losing shims or reusing incorrect shims: measure and keep shims in order; improper endplay leads to bearing failure or mis‑mesh.
- Reusing snap rings: they can fatigue; replace if any distortion.
- Not checking shift fork wear: grooved forks will cause misalignment and repeat failure; replace or reface.
- Pressing parts off unevenly: use press with proper supports to avoid shaft bending or scoring.
- Skipping bearing replacement: a noisy or rough bearing will quickly ruin a newly installed synchronizer.
- Not torquing to spec: results in leaks, misalignment, or failure — use torque wrench.
- Contamination: dirt or metal shavings will ruin synchro friction surfaces — keep everything clean and use filtered compressed air carefully.
- Incorrect gear oil or contaminated oil: use OEM spec fluid and new filter if applicable.

When to replace whole assembly
- If multiple gears and shafts show scoring, or shafts bent, or large chips present — replacement or full rebuild kit recommended.
- If hub/sleeve costs approach the price of a reman/rebuilt gearbox, consider replacement of the gearbox.

Final notes
- Always follow the Mitsubishi service manual for your Delica L300 for torque specs, shim thicknesses, and synchronizer orientation diagrams.
- Work methodically, tag components and take photos during disassembly to ensure correct reassembly.

End.
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