EXCELLENCE AUTO TECH | AUTOMOTIVE MECHANICS COURSE | ARTICLE 14 OF 116
The Manual Gearbox: Gear Ratios, Synchronizers, Engagement and Maintenance
Understand manual gearbox engineering, the torque path, synchronizer anatomy and the correct diagnostic methods.
By the end of this lesson, you should be able to:
- Explain the purpose of the manual gearbox.
- Calculate gear ratios and understand torque multiplication.
- Identify shafts, gears, forks, hubs, sleeves and synchronizers.
- Explain how forward gears and reverse are formed.
- Recognize the differences between clutch, selection and synchronization faults.
- Apply technical criteria when choosing the lubricant.
1. Why does the manual gearbox still matter?
Even with the spread of automatics, dual-clutch transmissions and CVTs, the manual gearbox remains essential in training automotive maintenance professionals.
It brings together fundamental concepts of gears, friction, torque, speed, lubrication and mechanical selection. Knowing how it works also makes it easier to understand other transmission architectures.
In light and utility vehicles, the manual gearbox is often valued for direct control of the gears and relatively simple construction in many applications. However, efficiency, durability and maintenance cost depend on the design and use, not just the type of transmission.
1.1 The problem the gearbox solves
A combustion engine does not deliver the same torque at all speeds. To pull away, climb hills, carry loads and maintain cruising speed, the vehicle needs different combinations of force and speed at the wheels.
The gearbox makes it possible to select these combinations. In the lower gears, available output torque increases while rotational speed decreases. In taller ratios, output speed approaches or may exceed input speed.
Diagram 1 — Torque path in the manual gearbox
Conceptual flow of a conventional drivetrain. The physical layout varies with the architecture.
2. Torque, power and gear ratio
2.1 Torque is not power
Torque is the moment of force acting on a shaft. Speed is how fast that shaft turns. Power represents the rate of energy transfer.
P = power in watts; T = torque in N·m; ω = angular velocity in rad/s.
A transmission does not create power. It trades speed for torque or torque for speed, with unavoidable losses from friction, oil churning and other phenomena.
2.2 How is the ratio calculated?
For a simple pair of external gears, the reduction ratio can be calculated from the number of teeth:
i = gear ratio; Z = number of teeth.
This formula applies to one gear pair. In gearboxes with multiple pairs, shafts and power paths, the overall ratio must consider all the stages involved.
2.3 Practical example: 3:1 reduction
Imagine a 20-tooth driving gear turning a 60-tooth driven gear.
Diagram 2 — Reduction ratio
The output turns three times more slowly than the input.
Teaching representation of gears; the circles do not reproduce the real tooth geometry.
If the input is at 3,000 rpm, the output of this stage will be about 1,000 rpm. With 100 N·m at the input and a hypothetical efficiency of 95%, the output torque will be:
The increase in torque comes with a reduction in speed. The real value depends on the losses in the assembly.
3. Reduction, direct drive and overdrive
3.1 Reduction ratio
When the ratio is greater than 1:1, the output turns more slowly than the input. This is typical of the launch gears.
The first gears help overcome the initial resistance to motion, slopes and loads.
3.2 Direct drive — 1:1
A direct ratio means input and output turn at the same speed, although there may be differences in the mechanical path and losses.
In some longitudinal gearboxes, direct drive can be achieved by coupling the shafts together. It is not correct to say that it always corresponds to fourth gear or that it necessarily depends on gears of the same size.
3.3 Overdrive
A ratio below 1:1 indicates that the output turns faster than the input, considering the reference points of the ratio analyzed.
This feature can lower engine speed when cruising, but the economy depends on the load, calibration and powertrain.
| Ratio | Example | Output speed | Characteristic |
|---|---|---|---|
| Reduction | 3.50:1 | Lower than input | Favors torque. |
| Direct | 1.00:1 | Equal to input | Does not change the speed ratio. |
| Overdrive | 0.80:1 | Higher than input | Favors lower engine speed when cruising. |
3.4 Final drive ratio
The differential also has a gear ratio. To find the overall reduction between engine and wheels, multiply the gear ratio by the final drive ratio, ignoring any other stages that may exist.
First gear of 3.50:1 and a 4.10:1 differential:
3.50 × 4.10 = 14.35:1
Ideally, the drivetrain provides an overall reduction of 14.35 times between the gearbox input and the wheels.
4. Internal architecture of the manual gearbox
Manual gearboxes vary with engine position, drive type and number of gears. The most common components include:
- Case: supports the internal assemblies and holds the lubricant.
- Input shaft: receives torque from the clutch.
- Countershafts and output shafts: take part in torque transmission, depending on the design.
- Gears: establish the different ratios.
- Bearings: support the shafts and allow them to rotate.
- Synchronizers: make it easier to couple components turning at different relative speeds.
- Fork and sleeve: perform ratio selection.
- Shift linkage: transmits the lever movements.
- Seals and gaskets: help with sealing.
4.1 Constant mesh
In many modern manual gearboxes, the forward gear pairs remain in mesh. Shifting does not involve sliding a whole main gear into another.
What changes is the component locked to the shaft: the synchronizer assembly selects which ratio transmits torque.
Diagram 3 — Conceptual two-shaft architecture
Schematic illustration of shafts and gear pairs. It does not represent a specific gearbox or the real geometric tooth contact.
4.2 Helical teeth
Helical gears are common for forward gears because they provide progressive tooth contact and can reduce noise compared with some straight-cut configurations.
However, they also generate axial loads that must be supported by the bearings and the gearbox structure.
4.3 Bearings and clearances
Bearings keep the shafts in position. Excessive play can change tooth contact, produce noise and impair the alignment of the engagement assemblies.
Correct adjustment depends on each transmission’s tolerances. Generic preload or clearance values should not be applied.
5. Shift linkage, cables, rods and forks
5.1 From the driver’s hand to the gearbox
The lever movement must be transmitted to the transmission’s selector mechanism. This link may use flexible cables, rigid rods or other arrangements.
The assembly is often called the shift linkage. It converts the driver’s movements into gear selection and engagement.
Diagram 4 — Gear selection system
5.2 Symptoms of external problems
- Excessively loose lever.
- Difficulty finding a gear.
- Imprecise engagement.
- Abnormal lever movement.
- Engagement that improves after adjusting or repairing the external mechanism.
Before dismantling the gearbox, check the cables, bushings, mounts, ends and adjustments specified by the manufacturer.
5.3 Shift forks
The forks move the synchronizer sleeves. Wear at the contact points, distortion or faults in the selector mechanism can prevent correct movement.
A gear jumping out may be related to the fork, sleeve, dog teeth, bearings, misalignment or other components. The symptom should not automatically be blamed on a single part.
6. Hub, sleeve and dog teeth
The hub is coupled to the shaft, usually by splines. The sleeve slides over the hub, guided by the fork, to connect the selected gear to the shaft.
The dog teeth must be intact and correctly positioned. Wear, rounding or incomplete travel can cause selection difficulties and unintended disengagement.
Diagram 5 — Hub and engagement sleeve
Functional diagram, without splines or tooth geometry.
7. The synchro ring: the gearbox’s micro-clutch
The synchronizer is one of the most important assemblies for smooth gear changes.
In a constant-mesh transmission, different components may turn at different speeds. Before the mechanical lock-up occurs, these speeds must be matched.
7.1 Operating principle
In a conventional synchronizer, conical surfaces come into contact under pressure. Friction generates synchronizing torque, bringing the speeds of the components to be coupled closer together.
The blocking mechanism prevents the dog teeth from meeting prematurely while there is a significant speed difference.
7.2 Synchronization sequence
- The driver moves the lever.
- The selector moves the fork.
- The fork moves the sleeve.
- The assembly applies force to the synchronizing surfaces.
- Friction reduces the speed difference.
- The mechanism lets the sleeve pass.
- The dog teeth connect the gear to the shaft.
Diagram 6 — Stages of synchronized engagement
The sleeve starts to advance and the synchronizer receives an axial load.
Friction between the conical surfaces brings the speeds closer.
The sleeve reaches the dog teeth and connects the gear to the shaft.
7.3 Materials and coatings
The rings may use copper alloys, ferrous materials or surfaces with specific coatings, including carbon-based friction materials, depending on the design.
Compatibility between material, geometry and lubricant directly affects operation.
7.4 Multi-cone synchronizers
Some transmissions use double or triple cone assemblies to increase synchronizing capacity without necessarily requiring more effort from the driver.
The number of cones and the arrangement vary with the transmission.
7.5 Why does a gear grind?
Grinding noise occurs when coupling happens without proper synchronization or when the engagement system meets abnormal resistance.
Possible causes include:
- Worn synchronizing surfaces.
- Unsuitable lubricant.
- Clutch that does not fully disengage.
- Clutch actuation problems.
- Worn sleeves and dog teeth.
- Selector mechanism faults.
When several gears are difficult with the engine running, investigate clutch disengagement first. When only one gear grinds repeatedly, the investigation should include its synchronizer and engagement assembly.
8. How does reverse gear work?
In many conventional manual gearboxes, reverse uses an idler gear to reverse the direction of rotation transmitted between the shafts.
This gear changes the direction of rotation, allowing the vehicle to move backwards without reversing the engine’s rotation.
Diagram 7 — Reversal of rotation in reverse gear
Each contact between external gears reverses the direction of rotation. The final direction in reverse depends on the complete architecture; this drawing shows the role of the idler gear.
8.1 Why do some reverse gears grind?
Historically, many transmissions used an unsynchronized reverse. If internal components were still turning, engagement could produce noise.
However, some modern transmissions have a synchronized reverse or specific engagement aids. So you should not generalize.
8.2 Correct practice
Before selecting reverse, bring the vehicle to a complete stop, press the clutch fully and follow the manufacturer’s instructions.
If reverse grinds repeatedly with the vehicle stationary, investigate clutch drag, actuation adjustment and selector mechanism operation.
9. Comparison of components and symptoms
| Component | Function | Possible symptom | Check |
|---|---|---|---|
| Synchro ring | Helps match speeds. | Gear grinding. | Condition of cone, ring and clearances. |
| Sleeve and hub | Couple the gear to the shaft. | Hard engagement or gear jumping out. | Teeth, splines and travel. |
| Cables and shift linkage | Transmit the command. | Play and imprecision. | Bushings, ends and adjustment. |
| Forks | Move the sleeves. | Incomplete engagement. | Wear and alignment. |
| Bearings | Support the shafts. | Growl and play. | Noise, play and oil condition. |
| Reverse gear | Takes part in reversing the motion. | Noise or difficult engagement. | Teeth, alignment and selection. |
The manual gearbox depends on gear ratios, shaft alignment, synchronization and precise selection. Understanding the torque path and the engagement sequence makes it possible to interpret symptoms more reliably and reduce unnecessary disassembly.
EXCELLENCE AUTO TECH | ARTICLE 14 OF 116 | PRACTICAL SECTION
The Manual Gearbox: Lubrication, Faults, Tests and Repairs
Workshop procedures, differential diagnosis, component inspection and technical assessment.
You will learn to select the correct lubricant, interpret symptoms, check clutch actuation, assess the shift linkage, recognize internal faults and structure a repair on technical grounds.
10. Manual gearbox lubrication
Manual transmission lubricant protects gears, bearings and internal surfaces. In many gearboxes, it also directly affects synchronization quality.
During operation, the oil is subjected to shear, temperature variations and contact with particles from normal or abnormal wear of the components.
10.1 Functions of the oil
- Reduce friction and wear.
- Protect the gear teeth.
- Help dissipate heat.
- Protect bearings and metal surfaces.
- Contribute to synchronizer behavior.
- Reduce corrosion and oxidation.
10.2 What do 75W-80 or 75W-90 mean?
SAE J306 classifications describe the viscosity characteristics of gear lubricants.
The number followed by W relates to low-temperature performance requirements. The second number, when present, relates to the viscosity range at high temperature.
Oils with different classifications should not be substituted just because they seem close.
Diagram 8 — Viscosity identification
Example reading of an SAE 75W-80 oil. Viscosity alone does not determine compatibility with a transmission.
11. API GL-4 and GL-5: what does the mechanic need to know?
The API GL-4 and GL-5 classifications relate to performance requirements for gear lubricants under different service conditions.
In general terms, GL-5 products are formulated to meet high wear and load protection requirements in certain applications, especially hypoid assemblies.
However, this does not mean that every GL-5 oil is suitable for any manual gearbox, nor that all GL-5 products necessarily attack bronze or brass.
11.1 Why does compatibility matter?
Synchronizers depend on specific friction characteristics. An oil with unsuitable additives or behavior can impair engagement even if it protects the gear teeth well.
In addition, chemical compatibility with metals and friction materials depends on the product’s formulation.
Do not replace GL-4 with GL-5 — or the other way round — without confirming the specification required by the transmission manufacturer. Also check viscosity, approvals and any automaker-specific requirements.
| Characteristic | API GL-4 | API GL-5 |
|---|---|---|
| Applications | Used in many manual transmissions. | Common in differentials and other specified applications. |
| Protection under load | According to GL-4 requirements. | According to GL-5 requirements. |
| Synchronizers | Depends on formulation and approval. | Depends on formulation and approval. |
| Interchangeability | Do not assume. | Do not assume. |
11.2 Is differential oil always the same as gearbox oil?
No. Even when they have similar viscosity grades, the products may meet different friction and additive requirements.
In some vehicles, the gearbox and differential share the same lubricant. In others, they are separate assemblies with different specifications.
12. When should manual transmission oil be changed?
There is no universal interval valid for all manual gearboxes.
The manufacturer may set periodic changes, scheduled inspections or different guidance depending on the type of use. Under severe conditions, there may be specific requirements.
Even when the manual does not call for periodic changes, the professional should investigate leaks, contamination, repairs and other conditions that justify intervention.
12.1 Factors that need attention
- Unknown maintenance history.
- Leaks from seals or gaskets.
- Water ingress or contamination.
- Overheating.
- Abnormal presence of metal particles.
- Recent internal repair.
- Severe use as defined in the documentation.
12.2 Why not recommend 60,000 km for everyone?
A generic recommendation may bring forward unnecessary services on some transmissions and delay maintenance on others.
The right approach is to identify the transmission and consult its service plan. In a workshop, the recommendation must be technically justified.
The expression “lubricated for life” does not mean the oil is immune to aging, contamination or losses. It means the maintenance strategy was defined by the manufacturer for certain conditions and service expectations.
13. General oil change procedure
This guide is for teaching purposes. The sequence, access points and level condition must follow the vehicle’s documentation.
- Confirm the model and transmission code.
- Check the lubricant specification and quantity.
- Check the temperature and position required for the level check.
- Inspect for leaks and case condition.
- Lift and support the vehicle correctly.
- Confirm the fill plug can be opened before draining.
- Collect the used oil in a clean container for inspection.
- Examine plugs and magnets, where fitted.
- Fit new seals when required.
- Fill with an approved product.
- Check the level using the specified method.
- Inspect for leaks and test operation.
- Record the work and dispose of the used oil correctly.
13.1 What to look for in the drained oil?
A small amount of fine material stuck to a magnet can occur depending on the design and use. However, fragments, large particles or significant contamination require investigation.
It is not correct to automatically identify golden particles as normal synchronizer wear. The composition and origin of the material must be assessed.
Plugs may use washers, sealing rings, sealants or specific geometries. Overtightening can damage the case thread. Use the torque specified by the manufacturer.
14. Driving habits that accelerate wear
14.1 Resting a hand on the lever
Keeping constant pressure on the lever can transmit unwanted loads to the selector mechanism in certain architectures.
The recommended habit is to take your hand off the lever after completing the shift.
14.2 Not pressing the clutch fully
If the clutch does not disengage properly, some torque is still transmitted. This can make synchronization and engagement harder.
14.3 Forcing the gear
Applying excessive force when there is abnormal resistance can worsen damage to the selection system and internal components.
14.4 Downshifting without matching speed
Inappropriate downshifts can place high loads on the engine, clutch and transmission.
14.5 Engaging reverse while moving
This practice can cause noise and damage. The vehicle must be completely stationary before selecting reverse, as instructed by the manufacturer.
15. Differential diagnosis: clutch or gearbox?
A common mistake is to condemn the synchronizer when the real problem is clutch disengagement.
Diagnosis must consider whether the difficulty appears with the engine running or off, while moving, or with the assembly cold or hot.
Diagram 9 — Investigation guide for hard engagement
Investigate clutch drag and actuation.
Investigate shift linkage, selection and possible internal problems.
Initial guide. Behavior can vary with the fault; it does not replace specific diagnostic procedures.
15.1 Test with the engine off
If the lever resists even with the engine not running, the external mechanism and selection components deserve attention.
15.2 Test with the engine running
If engagement gets significantly worse with the engine running, investigate whether the clutch is failing to interrupt torque transmission properly.
15.3 Checking hydraulic actuation
On hydraulic systems, check fluid level, leaks, air in the system and actuator travel according to the specific procedure.
15.4 Checking cable actuation
Inspect adjustment, travel, play and the condition of the cable and its mounts.
16. Practical table of symptoms and causes
| Symptom | Possible causes | Initial investigation |
|---|---|---|
| First and reverse hard to engage | Clutch drag, actuation or selection. | Compare engine running and off. |
| Second gear grinds | Synchronizer, lubricant or disengagement. | Assess the conditions and frequency of the symptom. |
| Gear jumps out | Teeth, sleeve, fork, bearings or incomplete selection. | Check the external mechanism and clearances. |
| Growl while moving | Bearings, gears, differential or tires. | Relate the noise to speed and load. |
| Noise in neutral | Rotating components, clutch or bearings. | Compare with the pedal pressed and released. |
| Oil leak | Seals, gaskets, plugs or breather. | Clean and identify the source. |
| Excessively loose lever | Bushings, cables or selector mechanism. | External inspection before disassembly. |
17. Noise diagnosis
Transmission noises must be analyzed according to the gear, vehicle speed, applied load and clutch condition.
17.1 Noise that changes when the clutch is operated
Operating the clutch changes the speed and load conditions of components. A change in noise can guide the investigation, but does not on its own identify a specific bearing.
17.2 Noise present in one gear
If the noise occurs mainly in a particular ratio, the technician should consider the gears, bearings and loading conditions of that torque path.
17.3 Noise that follows vehicle speed
Also consider the differential, driveshafts, wheel hubs and tires. The source may be outside the gearbox.
17.4 Noise in reverse
Some transmissions have a characteristic straight-cut gear noise. This does not automatically mean a fault.
However, clicks, abnormal vibrations or a sudden increase in noise must be investigated.
18. Bench inspection of synchronizers and gears
Disassembly should only take place after a diagnosis that justifies it and with access to the transmission’s specific procedures.
18.1 Ring inspection
- Look for wear and damage on the friction surfaces.
- Inspect for cracks and distortion.
- Check the teeth and blocking areas.
- Measure clearances or heights according to the manual.
- Check compatibility of the replacement ring.
18.2 Sleeve and hub inspection
- Examine splines and teeth.
- Check for proper sliding.
- Inspect for distortion and uneven wear.
- Check the assembly orientation.
18.3 Gear inspection
- Check for chipped or cracked teeth.
- Examine the contact surfaces.
- Inspect bearing and support areas.
- Look for signs of overheating.
18.4 Measurements
Axial and radial clearances, preloads and other tolerances vary between transmissions. Use calibrated instruments and the values in the service manual.
Do not swap similar parts, do not reuse fasteners the manufacturer forbids reusing and do not fit bearings by applying force incorrectly. The installation method must suit the type of fit.
19. Removing and installing the gearbox
19.1 Preparation
- Consult the vehicle-specific procedure.
- Use a suitable lift and supports.
- Support the engine when necessary.
- Identify connectors, cables and lines.
- Check the mounting points.
- Set aside special tools.
19.2 Removal
The sequence may involve driveshafts, mounts, the starter motor, suspension components and clutch actuation elements.
The gearbox must not be held by unsuitable components or removed in an improvised way.
19.3 Installation
Check alignment with the engine and the condition of related components. Do not use bolts to force misaligned assemblies together.
Observe torques, seals, fluid and adjustment procedures.
19.4 Test after assembly
Confirm all gears engage, the clutch works, there are no leaks or noises, and behavior while driving is correct.
20. Case studies
Complaint: second gear grinds on quick shifts, mainly when cold.
Investigation: oil specification and condition, clutch actuation, selector mechanism and the second-gear synchronizer assembly.
Lesson: the symptom may involve more than one system; disassembly must be justified.
Complaint: the selected gear returns to neutral under certain conditions.
Investigation: external adjustment, fork travel, dog teeth, shaft play and mounts.
Lesson: do not automatically condemn the synchro ring.
Complaint: engagement improves when the engine is off.
Investigation: pedal travel, actuation, disc drag, hydraulic system and related components.
Lesson: the clutch must be investigated before dismantling the gearbox.
Complaint: noise increases with vehicle speed.
Investigation: oil level, bearings, differential, driveshafts, hubs and tires.
Lesson: locate the source of the noise before replacing components.
21. Diagnostic checklist
- □ Identify the transmission code.
- □ Record the customer’s complaint.
- □ Confirm the symptom under safe conditions.
- □ Compare engagement with engine running and off.
- □ Inspect clutch actuation.
- □ Inspect cables, rods and shift linkage.
- □ Check engine and gearbox mounts.
- □ Investigate leaks.
- □ Confirm the lubricant specification.
- □ Relate noises to speed and load.
- □ Assess whether disassembly is needed.
- □ Measure components according to the manual.
- □ Carry out the repair with the correct parts.
- □ Check the oil level.
- □ Carry out a final functional test.
22. Safety and good practice
- Never work under a vehicle supported only by a jack.
- Use suitable equipment to support the transmission.
- Do not touch rotating components during tests.
- Avoid contact with hot oil.
- Use the correct tools and measuring devices.
- Do not force engagements to reproduce symptoms.
- Do not road test with faults that compromise safety.
- Send used lubricants to authorized companies.
23. Technical assessment — 10 questions
Choose the correct answer and check the commented answer key.
A) To create additional power.
B) To adapt torque and speed through gear ratios.
C) To replace the differential.
D) To eliminate the clutch in all designs.
A) 1:3.
B) 1:1.
C) 3:1.
D) 6:1.
A) Overdrive, given defined input and output.
B) A 4:1 reduction.
C) Necessarily reverse gear.
D) No torque transmission.
A) To cool the engine.
B) To control the fuel.
C) To increase tire pressure.
D) To bring relative speeds closer before coupling.
A) Flywheel.
B) Engagement sleeve.
C) Radiator.
D) Brake piston.
A) To raise the oil temperature.
B) To eliminate the bearings.
C) To help reverse the direction of rotation transmitted.
D) To prevent use of the clutch.
A) The specification approved by the manufacturer must be used.
B) All GL-5 immediately destroys any synchronizer.
C) GL-4 and GL-5 are always interchangeable.
D) Viscosity is the only relevant criterion.
A) Lighting system.
B) Rear tires.
C) Cooling system.
D) Clutch disengagement and actuation.
A) Only a dirty air filter.
B) Worn dog teeth or sleeve, or incomplete selection.
C) Only tire pressure.
D) Exclusively accelerator pedal wear.
A) Necessarily every 10,000 km.
B) Only after the transmission breaks.
C) According to the manufacturer’s specification and maintenance plan.
D) Exactly every 60,000 km on all vehicles.
24. Answer key with comments
1. B — Adapt torque and speed.
The ratios match engine operation to the needs of the wheels.
2. C — 3:1.
Dividing 60 teeth by 20 teeth gives a 3:1 reduction.
3. A — Overdrive.
A ratio below 1:1 indicates an output faster than the input, at the defined points.
4. D — Bring speeds closer.
The synchronizer uses friction to make mechanical coupling easier.
5. B — Engagement sleeve.
The sleeve slides over the hub and helps lock the gear to the shaft.
6. C — Reverse the direction of rotation.
The idler gear is part of the reverse torque path in many architectures.
7. A — Follow the manufacturer.
API classification, viscosity and approvals must be compatible with the transmission.
8. D — Check the clutch.
The difference between engine running and off suggests investigating drag and actuation.
9. B — Engagement or selection components.
Teeth, sleeves, forks and clearances may be involved in the fault.
10. C — According to the manufacturer.
There is no universal change interval for all manual gearboxes.
25. Final summary of the lesson
- The manual gearbox adapts torque and speed.
- The ratio depends on the power path and the gears involved.
- Lower gears favor output torque.
- A direct ratio is 1:1, but it does not necessarily belong to fourth gear.
- Constant mesh keeps several gear pairs in contact.
- The shift linkage transmits the lever movements.
- The forks move the sleeves.
- Synchronizers bring speeds closer before engagement.
- Reverse gear may use an idler gear.
- The oil must meet the transmission’s exact specification.
- GL-4 and GL-5 are not automatically interchangeable.
- Hard engagement does not necessarily mean a faulty synchronizer.
- A gear jumping out may involve different components.
- Diagnosis must start with non-invasive inspections and tests.
26. Technical references for professional application
Before carrying out work, consult the vehicle or transmission manufacturer’s specific information:
- Gearbox identification.
- Gear ratios and shaft architecture.
- Oil specification and capacity.
- Level check procedure.
- Tightening torques.
- Assembly clearances and tolerances.
- Removal and installation procedures.
- Special tools.
- Technical bulletins and updates.
Technical knowledge, precise diagnosis and excellence in automotive maintenance.
Article 14 of 116 — The Manual Gearbox.