Quick overview (what and why)
- The transmission output shaft is the driven shaft inside a manual gearbox that carries the gears that send power out to the driveshaft or final drive. If the output shaft or its bearings/seals fail you’ll get noise, vibration, leaks, loss of drive or gear engagement problems.
- The repair replaces a worn or damaged output shaft and associated bearings/seals, and restores proper alignment and preload so the gearbox runs quietly and transfers power reliably.
- Think of the gearbox like a well-organized gear train in a hand tool: the input shaft brings power in, the layshaft (if present) and output shaft route that power out through meshing gears; bearings keep the shafts spinning precisely on their axes, seals keep the oil in. If the axle in a bicycle wheel were bent or its bearings shot, you’d get wobble and rough rolling — the output shaft problem is the same idea inside the transmission.

Before you start — safety and mindset
- This is heavy, precise mechanical work. You will need a level workbench, a transmission jack (or equivalent), good lighting, clean rags, parts trays, and the factory service manual (FSM) for your specific Nissan model and gearbox for exact torque, shim thicknesses and clearances.
- Safety: disconnect the battery, use jack stands (never rely only on a hydraulic jack), wear eye protection and gloves, use a transmission jack to support the gearbox, label and bag fasteners and shift parts as you remove them. If you aren’t comfortable with press-fitting bearings or measuring gear backlash and bearing preload, consider a transmission shop.

Tools and consumables you’ll need (typical)
- Full set of metric sockets and wrenches, extensions, breaker bar
- Screwdrivers, snap-ring pliers (internal and external), drift punches
- Bearing puller and/or hydraulic press (or shop that will press bearings)
- Gear puller, soft-faced hammer
- Transmission jack or heavy-duty floor jack with a wood block
- Torque wrench capable of required ranges (low and high)
- Feeler gauges, dial indicator with magnetic base, plastigauge (for end float/preload check)
- Punches, drift, bench vise
- New output shaft (correct part), new bearings, new oil seals, circlips/snap rings, any shims recommended by FSM, gear oil and gasket/sealant
- Clean solvent, gear oil drain pan, rags, thread locker (if specified)

Major components you will encounter (what each does)
- Input shaft: receives power from the clutch/engine. Rotates inside bearings.
- Lay/cluster shaft (if present): carries input-driven gears that mesh to output shaft gears.
- Output shaft (the part you’re replacing): holds driven gears that transfer power to the final drive/driveshaft; splines at the end engage the propeller/driveshaft/flange.
- Gears: spur/straight-cut face gears that mesh with lay/cluster or other gears to produce each ratio.
- Synchronizer hubs and rings: provide smooth engagement between gear and shaft when shifting (typical in synchromesh transmissions).
- Shift forks and rails: move synchronizer hubs into position when you change gears.
- Bearings: cylindrical/roller or ball bearings supporting radial and axial loads on shafts. Output shaft typically has at least one radial bearing (and sometimes a thrust bearing) at the rear/front.
- Seals (output seal, front seal): prevent oil leaking where the shaft exits the case.
- Snap rings, spacers, thrust washers, shims: locate gears and set axial clearance (end float) and bearing preload.
- Case halves (or single case): hold everything. Mating surfaces require clean reassembly and correct gasket/sealant.

Theory — how it works and what wears
- Power flow: engine → clutch → input shaft → gears (meshing with output shaft gears) → output shaft → driveshaft → differential → wheels.
- Bearings keep shafts concentric. If bearings wear, the shaft can move radially or axially, causing gear misalignment and uneven tooth loading → noise, gear tooth damage, wear.
- End float is axial movement along the shaft. Too much end float causes clashing and poor synchronizer operation; too little (excessive preload) causes overheating and early bearing failure.
- Seals prevent oil loss. Without oil the gear teeth and bearings overheat and fail quickly.
- Causes for output shaft replacement: scored or broken shaft splines, severe wear at gear mounting surfaces, deep grooves from failed bearings, bent shaft from an impact, or irreparable damage to splines that connect to the driveshaft flange.

High-level step-by-step procedure (beginner-focussed, bench-level detail)
Note: Always cross-check with factory service manual for your exact gearbox model (YD22DDTi can be in different Nissan models and gearboxes). These steps are comprehensive but generic. I will not provide numerical torque values — use the FSM.

1) Preparation
- Gather parts, tools, manual. Clean work area and set bench with trays.
- Drain transmission oil. Catch fluid and dispose/recycle properly.
- Raise vehicle and remove driveshaft/propeller shaft(s). Mark orientation so reinstallation is in same position.
- Remove clutch pressure plate and flywheel if transmission removal requires it (or at least separate gearbox from engine).
- Disconnect linkages, speedometer/counter sensor, electrical connectors, and any mounts that tie the gearbox to chassis or engine.
- Support transmission with a transmission jack.

2) Remove the transmission from vehicle
- Unbolt bellhousing from engine block (support transmission with jack). Slide transmission away from engine input shaft — be careful of clutch alignment and pilot bearing.
- Lower gearbox to bench with the jack.

3) Strip down the transmission on the bench
- Clean the exterior before opening to minimize contamination.
- Remove top cover/shift housing components to access internal selectors and forks. Photograph or label positions — indexing shifts is critical.
- Remove shift forks and rails; keep forks matched to rails and associated selector positions.
- Remove snap rings, circlips and hub assemblies to release synchronizers and gears. Use snap-ring pliers and keep each ring in a labeled bag.
- Remove gears: slide them off the output shaft. If they’re pressed or tight, use gear puller or soft drift and hold shaft securely.
- Remove the output shaft’s retaining snap rings and any thrust washers or spacers. These locate the shaft axially.
- Push or press the output shaft out of the case assembly. Depending on gearbox design, you may need to remove the layshaft first or press bearings off. Use a press or arbor and protect the shaft surfaces.

4) Inspect components
- Output shaft: check splines, journal surfaces, keyways, gear mounting faces. Replace if any scoring, pitting, or spline wear beyond limit.
- Gears: inspect teeth for pitting, chipped teeth, unusual wear, discoloration (overheat).
- Bearings: replace all output shaft bearings and possibly input/lay shaft bearings if they show wear. Bearings are cheap insurance.
- Thrust washers and shims: inspect for wear and flatness. Replace if worn.
- Case bores and surfaces: inspect for wear where bearings locate.
- Seals: definitely replace output oil seal and any associated seals.

5) Fit new output shaft and bearings
- Clean all mating surfaces. Heat the case or cool bearings (bearing chilling with freezer) if needed for interference fits to press or slip on easily.
- Press bearings onto the new output shaft in the correct orientation (note any locating shoulders or races). If bearings have an inner and outer race orientation, ensure correct placement relative to the shaft and case.
- Install bearing spacers, thrust washers and circlips as removed. Use the original arrangement unless the FSM calls for replacement shims. Do not mix up thicknesses — they control axial clearance.
- Before final assembly: check end float (axial play) using dial indicator. Compare to FSM spec. If out of spec, adjust shims or preload per FSM (some transmissions use shims behind bearings or adjustable collars).
- If preload is set by a crush sleeve or bearing preload washer, install as instructed by FSM and re-measure.

6) Reassemble gears and synchronizers
- Slide gears and synchronizer hubs back onto the output shaft in the original order/position. Install new snap rings and any locking devices.
- Check gear mesh visually (teeth contact pattern) if possible after partial assembly; however final gear mesh is typically set by pinion/differential side, not by transmission internals in manual trans — still, gears should seat fully and spin freely on the shaft.
- Reinstall shift forks and rails, ensuring forks engage the synchronizers and rails are in the correct indexed positions. Use photos/labels you made earlier.

7) Close the case and reinstall
- Clean mating surfaces and use appropriate gasket or sealant per FSM. Torque all case bolts to FSM sequence and spec.
- Reinstall any external components (speedometer drive, sensors, mounts).
- Reinstall transmission into vehicle using transmission jack: line up input shaft with clutch disc/pilot bearing carefully. Slide bellhousing to engine and bolt up using correct pattern and torque.
- Reconnect driveshaft, linkage, electrical connectors, fluid fill plug.

8) Fill and test
- Refill transmission with correct gear oil to correct level.
- Start vehicle and check neutral gear engagement and smoothness of shifting before moving.
- Road test under light and increasing load to verify noise gone, no leaks, correct shifting and no vibration.
- Recheck oil level after warm-up.

Common mistakes and what can go wrong (how to avoid them)
- Missing or mis-ordered shims/circlips: You must reinstall in the original order. Label everything. Incorrect shim thickness leads to excessive end float or preload causing noise or premature bearing failure.
- Improper bearing installation: Pressing on the wrong race destroys the bearing. Always press on the race that is being pressed and protect surfaces.
- Incorrect torque or loose fasteners: Can lead to case separation or bearing preload changes. Use torque wrench and FSM specs.
- Dirty work: contamination (dirt, metal shavings) causes premature wear. Clean parts, keep bearings sealed until install.
- Improper seal installation: damaged or mis-seated seals leak. Use proper seal drivers and replace old seals.
- Damaging splines: avoid hammering the driveshaft flange on/out of splines. Align and use proper puller/press.
- Not replacing all worn bearings: old bearings will quickly spoil a new shaft. Replace bearings on input and layshaft if there was evidence of wear.
- Incorrect reassembly of shift forks/hubs: will cause missed gear engagement or internal damage. Index forks carefully.
- Not checking end float/bearing preload: this leads to noise and shortened part life.
- Not using FSM torque and clearance specs: generic advice can’t replace exact manufacturer specs. The FSM is authoritative.

Troubleshooting after reassembly
- Whine/singing noise: typically bearing preload or gear alignment; check bearings and end float.
- Clunk on acceleration: could be excessive end float, missing spacers, or damaged splines on driveshaft engagement.
- Leak at output: seal installed backwards or cut seal; replace seal.
- Hard shifting or gears popping out: misadjusted selectors, worn synchronizer, or incorrect fork placement.
- Vibration/shudder: misaligned driveshaft, improper driveshaft balance after reinstallation, or bent output shaft (rare if replaced).

Final notes and best practices
- Use the FSM. Exact bearing part numbers, shim thicknesses and torque sequences vary by gearbox model; the YD22DDTi can be fitted to different transmissions; match to your VIN and gearbox code.
- Replace bearings and seals as a set. Bearings are inexpensive compared to the labor of removing the box again.
- Take photos at every stage. Label small parts in sequence on a board (magnetic tray or tape with numbers).
- If you need a press for bearing work and don’t have one, many shops will press-fit bearings inexpensively. Consider contracting the pressing steps if you lack equipment.
- If you’re unsure about checking gear mesh, bearing preload, or shims — get the gearbox checked by a transmission shop. It’s better than a premature rebuild.

This covers the detailed components you’ll see, why the repair is needed, how the system works, and step-by-step replacement guidance aimed at a beginner mechanic. Follow the factory service manual for exact specifications and sequences; keep work clean and methodical.
rteeqp73

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Change Main bearings with crankshaft still installed Changing main bearings on crankshaft.

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