Summary theory (one paragraph)
- A planetary gearbox consists of a sun gear, several planet gears mounted on a planet carrier, a ring (internal) gear and bearings that set the relative positions. Power input/ratio is created by the interaction and relative stiffness/clearances of those parts; bearing preload and tooth backlash control load distribution and noise. Failures (tooth wear, pitting, bearing failure, contamination) change gear alignment and clearances, causing noise, vibration, overheating, loss of drive or premature wear. Replacing worn planetary gears and associated bearings/seals restores correct geometry, preload and lubrication, which restores load distribution, contact pattern and service life.

Ordered repair procedure with theory integrated (concise)
1) Safety & preparation
- Park on level ground, chock wheels, disconnect battery, drain gearbox oil into a clean container, wear PPE. Theory: clean oil removal prevents contamination of work area and allows inspection for metal particles that indicate failure mode.

2) Diagnose & document symptoms
- Note noise, shift problems, oil condition, metal debris on drain plug/magnetic plug. Photograph and mark housing/shafts for reference. Theory: debris pattern indicates whether planet teeth, sun, ring or bearings failed.

3) Remove gearbox from vehicle (if required by GH1H layout)
- Support gearbox, disconnect linkages, driveline, mounts and hydraulics, then remove. Theory: full disassembly off-vehicle gives accurate alignment control and access to necessary tools (press, fixtures).

4) External disassembly
- Remove cover(s), input/output shafts and ancillary parts to access planetary assembly. Keep parts in order and tagged. Theory: sequential removal preserves timing and orientation references for reassembly and for correct backlash settings.

5) Expose planetary carrier & ring gear
- Remove bolts securing carrier/ring gear and any retaining circlips or snap rings. Remove carrier assembly with planets as a unit if possible. Theory: carrier removal allows direct inspection of planet bearings and gear tooth surfaces.

6) Inspect components and collect measurements
- Clean parts with solvent. Inspect planet gear teeth, sun gear, ring gear for pitting, spalling, scoring, edge break, wear pattern. Check bearings for roughness, axial/radial play. Check splines for wear. Measure backlash between sun/planet and planet/ring with a dial indicator, measure runout and bearing bores for ovality. Record thicknesses of shims/spacers. Theory: determining what is worn and how much clearance has changed identifies which parts must be replaced and what shims/preloads must be reset to restore geometry.

7) Decide replacement scope
- Replace planet gears and planet carrier bearings if any damage; replace sun or ring gear if teeth are scored/pitted beyond acceptable limits; always replace all bearings and seals in the assembly and any soft fasteners, circlips, gaskets. Theory: mixing new and heavily worn gears shifts load to remaining old teeth and causes rapid failure — replace the load-bearing elements together.

8) Remove planet gears and bearings
- Press out planet gear assemblies from the carrier, press out bearing races, replace bearing bores or carriers if damaged. Keep planets indexed to their carrier positions when possible. Theory: press-fit parts can alter clearances; accurate replacement maintains the original geometry for measured shims.

9) Fit new parts and replace bearings/seals
- Install new planet gears, bearings, races, seals, sun/ring gear as needed. Use correct interference fits, heat/press techniques per manual. Use new circlips, locking devices and approved adhesives where specified. Theory: new bearings restore preload and positional accuracy; new seals prevent contamination and oil loss that led to failure.

10) Pre-assembly checks: wearing-in and orientation
- Reassemble planets into carrier with the same orientation; torque planet shaft/bolts to spec. Fit the carrier to the ring/sun without final shims to check gross fit. Theory: orientation and correct torque prevent eccentric loading of planets and improper contact patterns.

11) Set bearing preload and backlash (critical)
- Reinstall carrier into housing with the original or new shims/spacers. Use a dial gauge to measure backlash between sun and ring and adjust with shims until specified backlash is achieved. Set bearing preload by installing preload shim/nut and measuring rotation torque or bearing axial play as specified. Theory: backlash controls where teeth contact; bearing preload maintains fixed geometry under load. Correct values restore correct contact pattern and prevent edge loading and noise.

12) Check tooth contact pattern
- Apply gear marking compound or Prussian blue to a tooth and rotate under load to check contact patch across tooth face; adjust shims if patch is mislocated (toward face or root). Theory: proper contact distribution means load is shared across full tooth width and root, avoiding concentrated stress and premature failure.

13) Final assembly
- Fit covers, seals and torque all bolts to workshop manual specs, replace gaskets, and ensure venting/breathers are correct. Refill with manufacturer-specified gear oil to correct level. Theory: correct sealing and correct lubricant viscosity/level ensure proper film thickness and cooling, preventing re-contamination or starvation.

14) Bench/initial run test
- Rotate assembly by hand to verify smoothness and that rotation torque and backlash are within spec. If possible, bench run at low speed/load, check for noise and leaks. Theory: early detection of misassembly or incorrect preload prevents catastrophic failure when returned to service.

15) Refit gearbox to vehicle and road test
- Reinstall gearbox, reconnect linkages, fill to working oil level, run through gears under light load, then perform load tests. Monitor oil temperature and sound. Recheck oil and drain plug for metal particles after initial run-in. Theory: running under controlled conditions verifies load distribution and allows detection of remaining issues before full service.

How the repair fixes common faults (mapping faults to actions)
- Tooth wear/pitting: replacing planet/sun/ring gear restores proper tooth profiles. Resetting backlash and contact pattern ensures even load sharing; this eliminates edge loading that caused pitting.
- Bearing failure: replacing bearings and setting correct preload restores shaft/gear positional stability; eliminates radial/axial runout and excessive play that caused mis-meshing and noise.
- Metal debris/contamination: cleaning, replacing seals and oil removes sources of abrasive wear; new oil and seals prevent recurrence.
- Excessive backlash/noise: adjusting shims/backlash reduces gear lash to spec, moving contact patch to center of tooth face and removing lash-induced impact noise.
- Overheating or oil loss: new seals and correct oil restore lubrication film and cooling capacity, preventing overheating-related damage.

Practical notes (short)
- Always use factory workshop manual values for torque, shim thickness ranges, backlash and preload methods specific to GH1H. Incorrect preload or backlash is the most common cause of repeat failure.
- Replace fasteners, seals and circlips; use correct bearing fit techniques (heat or press). Do not reuse bearings if doubtful.
- Keep everything scrupulously clean; contamination during assembly kills gearboxes.
- If you find multiple damaged components (ring gear, sun and planets), replace the lot rather than mixing old/new gears.

Done.
rteeqp73

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