Gearbox Inspection (a):
A gearbox inspection is a crucial step in diagnosing potential problems and ensuring the continued smooth operation of a vehicle’s drivetrain. Here’s a breakdown of a typical gearbox inspection:
External Inspection:
- Visual Inspection: The mechanic will first visually inspect the gearbox housing for any cracks, leaks, or signs of external damage. This might involve removing any underbody panels for better access.
- Gearshift Linkage: The condition of the gearshift linkage and its components (cables, rods, bushings) will be checked for wear, looseness, or damage which could cause shifting difficulties.
Internal Inspection (Requires Gearbox Removal and Disassembly):
- Gear Oil Inspection: The drained gearbox oil will be examined for its color, consistency, and presence of metallic particles. Dark, burnt-smelling oil, or presence of metal shavings could indicate internal wear or damage.
- Gear and Bearing Inspection: Each gear and bearing will be thoroughly cleaned and inspected for:
- Pitting: Small indentations or craters on the gear tooth surfaces, indicating wear and potential for future breakage.
- Scoring: Scratches or grooves on the gear teeth, often caused by debris contamination or misalignment.
- Spalling: Flaking or breaking away of gear tooth material, a more severe form of wear.
- Cracks: Any cracks in gear teeth or bearing races can lead to catastrophic gearbox failure.
- Bearing Wear: Signs of wear or damage on bearing surfaces like pitting, discoloration, or roughness.
- Synchro Rings and Dog Teeth: These components responsible for smooth gear changes will be inspected for wear, chipping, or rounding of the teeth which can cause difficulty engaging gears.
- Shift Forks and Selector Rods: These components will be checked for wear or bending that could hinder proper gear selection.
Measurements:
- Gear clearances between meshing teeth might be measured to ensure they are within specifications. Excessive wear can increase clearances and lead to noisy operation.
- Bearing tolerances might also be checked to ensure proper fit and function.
Reassembly:
After a thorough inspection and replacement of any worn or damaged components, the gearbox will be reassembled using new gaskets and seals. The correct type and amount of gearbox oil will be refilled.
(b) Gear Tooth Faults (2):
- Pitting: This is a common fault where small indentations or craters appear on the gear tooth surfaces. Causes:
- Overload: Excessive torque or load on the gears can cause pitting due to high contact pressure.
- Contamination: Dirt, debris, or worn-out metal particles in the gearbox oil can act as abrasive elements and contribute to pitting.
- Improper Lubrication: Insufficient or low-quality gearbox oil can lead to increased friction and pitting.
- Reason for Concern: Pitting weakens the gear teeth and can eventually lead to tooth breakage if left unchecked. Early detection and replacement of affected gears is crucial.
- Spalling: This is a more severe form of wear where pieces of gear tooth material break away or flake off. Causes: Similar to pitting, overload, contamination, and improper lubrication can lead to spalling. Additionally, factors like:
- Fatigue: Repeated stress cycles on the gear teeth can cause metal fatigue and eventual spalling.
Reason for Concern: Spalling signifies significant wear and damage. The affected gear might need immediate replacement to prevent complete tooth fracture and potential gearbox failure.