EXCELLENCE AUTO TECH | AUTOMOTIVE MECHANICS COURSE | ARTICLE 13 OF 116
Automotive Transmissions: How They Work, Advantages, Disadvantages and Maintenance
Manual, automated, dual-clutch, conventional automatic and CVT: fundamentals for professional diagnosis.
On completing this material, the student should be able to identify the main types of transmission, explain how they work, recognize their components, compare their characteristics and understand the care needed for maintenance and diagnosis.
Important: service procedures, fluids, temperatures, torques and adaptations must follow the manufacturer’s specific documentation.
1. Introduction: why is the transmission so important?
Choosing a car involves much more than power, design and equipment. The type of transmission affects comfort, vehicle response, fuel consumption, driving style and maintenance cost.
The engine develops torque and power at different speeds. However, the wheels need a lot of force to start moving and longer ratios for travel at high speed.
The transmission adapts to these needs by changing the ratio between engine speed and the speed sent to the wheels.
Diagram 1 — Power path
Simplified flow. The layout of the assemblies varies with the vehicle’s architecture.
1.1 Torque, speed and power
Torque is the moment of force applied to a shaft. Speed indicates how many turns the shaft makes per unit of time. Power relates torque and angular velocity.
P = power in watts; T = torque in N·m; ω = angular velocity in rad/s.
The transmission does not create power. It changes the relationship between torque and speed, with losses from friction, fluid churning and other factors.
1.2 Gear ratio
A reduction ratio makes the output turn more slowly than the input, increasing the available torque, minus losses.
In a 3:1 reduction, the input shaft turns three times for each turn of the output shaft.
With an input torque of 100 N·m and a hypothetical efficiency of 95%, the output torque would be approximately:
100 × 3 × 0.95 = 285 N·m
2. Comparison of the main types of transmission
| Type | Principle | Characteristic | Maintenance focus |
|---|---|---|---|
| Manual | Clutch and gears selected by the driver. | Direct control. | Clutch, synchronizers and oil. |
| Single-clutch automated | Mechanical gearbox with actuators. | Automatic shifts with a possible torque pause. | Actuators and learning. |
| Dual-clutch | Two torque paths. | Potentially fast shifts. | Mechatronics, clutches and fluid. |
| Planetary automatic | Planetary gearsets and hydraulic control. | Comfort and a wide variety of designs. | ATF, pressures and friction elements. |
| CVT | Continuous variation of the ratio. | Linear response in many applications. | Fluid, pressure and temperature. |
3. Mechanical or manual gearbox
The manual gearbox is a system in which the driver chooses the gear ratio with the lever and controls disengagement from the engine using the clutch pedal.
3.1 Main components
- Flywheel.
- Clutch disc, pressure plate and release bearing.
- Input shaft and output shaft.
- Gears of different ratios.
- Synchronizer assemblies.
- Fork and selector mechanism.
- Bearings, seals and housing.
- Differential, when integrated in the gearbox.
3.2 How does the clutch work?
In a single-plate dry clutch, the pressure plate clamps the disc against the flywheel, allowing torque to be transmitted by friction.
When the pedal is pressed, the release mechanism reduces the clamping force. This allows the transmission to be disconnected from the engine to make shifting easier.
The disc may keep turning through inertia or drag. So disengaging does not mean all internal components stop immediately.
Technical box — Clutch engaged and disengaged
The pressure plate presses the disc against the flywheel. Torque is transmitted.
Clamping force is reduced. The coupling is interrupted or reduced.
Conceptual representation, not to mechanical scale.
3.3 What do the synchronizers do?
In synchromesh manual gearboxes, the gear pairs generally stay in mesh. Gear selection is done by sleeves and synchronizers.
The synchronizer uses friction to bring the relative speeds closer before engagement. When worn, it can cause difficult engagement or grinding noise.
3.4 Advantages
- Direct control of gear selection.
- Relatively simple construction in many applications.
- Possibly lower repair costs, depending on the model.
- Good mechanical efficiency in suitable designs.
3.5 Disadvantages
- Requires frequent use of the clutch.
- Can tire the driver in heavy traffic.
- Depends on driving technique for smooth shifts.
- Improper use can accelerate clutch wear.
3.6 Maintenance points
Inspect clutch actuation, leaks, noises, fluid condition and gear engagement.
Replacing the clutch kit should be based on diagnosis and the condition of the assembly. There is no universal replacement interval.
Avoid resting your foot on the clutch pedal, holding the car on hills by slipping the clutch and keeping unnecessary pressure on the gear lever.
4. Single-clutch automated gearbox
The automated gearbox, also called AMT in certain classifications, uses a mechanical gearbox with actuators that operate the clutch and select gears.
The driver does not need to use a clutch pedal. The electronic module calculates when to shift based on sensor information.
4.1 How does the shift happen?
- The module identifies the need to change ratio.
- Transmitted torque is reduced according to the strategy.
- The actuator disengages the clutch.
- The selector mechanism engages the new gear.
- The system re-engages the clutch in a controlled way.
Because there is a temporary interruption in torque, some shifts may be felt as pauses or slight fore-and-aft movements.
4.2 Additional components
- Clutch actuator.
- Selection and engagement actuator.
- Position sensors.
- Electronic control module.
- Harnesses, connectors and power supply.
- Hydraulic circuit, when present.
4.3 Advantages and disadvantages
Advantages: no clutch pedal is needed and it can use a relatively simple mechanical architecture.
Disadvantages: some applications have more noticeable shifts; maintaining the actuators and adaptation procedures requires specialized knowledge.
4.4 Possible faults
Clutch wear, faulty sensors, power supply problems, actuation faults and improper learning can compromise gear selection.
Some systems require learning of the clutch engagement point and actuator positions after work. Perform only the procedures specified by the manufacturer.
5. Dual-clutch transmission — DCT
The dual-clutch transmission uses two torque paths, each controlled by a clutch. In many applications, one path serves one group of gears and the other serves the remaining ratios.
While one ratio is transmitting torque, another can be prepared for the next shift.
Diagram 2 — Two transmission paths in the DCT
Conceptual diagram. How the ratios are distributed depends on the design.
5.1 Dry and wet clutches
Dry clutches do not run with their friction surfaces immersed in oil. Wet clutches use fluid for cooling and operation, depending on the architecture.
Neither is universally superior: the result depends on torque capacity, cooling, calibration and application.
5.2 Mechatronics
The mechatronic unit combines electronic control functions with hydraulic or electromechanical actuation. It can control gear selection, pressure and clutch engagement.
5.3 Advantages
- Fast shifts under suitable conditions.
- Potentially good energy efficiency.
- Automatic operation with no clutch pedal.
5.4 Limitations and precautions
- Greater control and repair complexity.
- Some architectures can overheat during prolonged maneuvering.
- Work may require specific tools and adaptations.
- Incorrect fluid can compromise operation.
In systems that control launch by slipping the clutch, avoid holding the vehicle on a slope using only the accelerator. Heed temperature warnings and the manufacturer’s guidance.
6. Conventional automatic transmission with planetary gears
The conventional automatic uses controlled internal elements to select different ratios without manual gear changes.
In many applications, the initial coupling between engine and transmission is done by a torque converter, while planetary gearsets and friction elements establish the ratios.
6.1 Torque converter
The converter uses fluid circulating between impeller, turbine and stator to transfer energy from the engine to the transmission.
Under certain conditions, the stator helps multiply torque. Transfer depends on the relative motion of the fluid and components.
6.2 Lock-up clutch
Many modern converters have an internal lock-up clutch. When commanded, it reduces hydrodynamic slip, improving efficiency under suitable conditions.
So it is wrong to say that conventional automatic transmissions have no clutches.
6.3 Planetary gearset
A simple planetary gearset has a sun gear, planet gears, a planet carrier and an internal ring gear. Different ratios are obtained by controlling the input, output and holding elements.
Diagram 3 — Simplified planetary gearset
Positional representation, without teeth or real bearing geometry.
6.4 Valve body and solenoids
The valve body distributes fluid to the hydraulic circuits. Solenoids control or modulate pressures according to the electronic module’s strategy.
The pressures operate internal elements such as friction clutches and brakes.
6.5 Advantages and disadvantages
Advantages: comfort, smoothness in many applications and potentially high durability when the assembly is correctly sized and maintained.
Disadvantages: internal complexity, potentially high repair costs and energy losses that vary with the design.
6.6 Maintenance points
Use the specified ATF, check the level using the correct procedure, investigate leaks and follow the manufacturer’s intervals.
There is no universal requirement to change the fluid by machine, and no method automatically guarantees complete fluid replacement.
7. CVT — Continuously variable transmission
The CVT allows the gear ratio to change continuously within an operating range.
In many automotive applications, the system uses two pulleys of variable effective diameter linked by a metal belt or chain.
7.1 How does it work?
The pulleys have movable conical faces. By changing the distance between these faces, the system changes the effective contact radius with the drive element.
When the drive pulley works with a smaller effective radius and the driven pulley with a larger one, there is a reduction ratio. When the opposite occurs, the ratio becomes taller.
Diagram 4 — Ratio variation in the CVT
Launch example
Drive smaller | Driven larger
High-speed example
Drive larger | Driven smaller
The circles represent effective contact radii, not the physical shape of the pulleys. The drive element is omitted for clarity.
7.2 Does a CVT have gears?
A pulley CVT does not rely exclusively on fixed ratios like a conventional gearbox. However, that does not mean it has no gears at all.
Some designs have auxiliary gears, reverse mechanisms or electronically simulated ratios.
7.3 CVT and e-CVT are not necessarily the same
Certain hybrid transmissions called e-CVT use planetary gearsets and electric machines to split power. They do not necessarily work with pulleys and a metal belt.
7.4 Advantages
- Continuous variation of the ratio.
- Smooth driving in many applications.
- Ability to keep the engine in a favorable operating range.
- Good efficiency in certain powertrains.
7.5 Disadvantages
- Acceleration feels different from conventional shifts.
- Possibility of high, constant engine speed under hard acceleration.
- Specialized repairs in certain architectures.
- Sensitivity to fluid specification and pressure control.
7.6 Maintenance and care
Use only the approved fluid, respect the level-check and temperature conditions, and do not exceed the load and towing limits set by the manufacturer.
Noises, vibrations and changes in behavior in a CVT need diagnosis. Not every vibration indicates a belt or chain fault, and not every failure can be solved with a fluid change.
8. Which transmission is most economical and durable?
There is no universal winner. Consumption depends on the combination of engine, transmission, vehicle mass, available ratios, control strategy and conditions of use.
Likewise, durability depends on the design, sizing, temperature, maintenance, usage history and quality of repairs.
The professional must identify the architecture before diagnosing. Manual, automated, DCT, planetary automatic and CVT can show similar symptoms but use different components, fluids and service methods.
EXCELLENCE AUTO TECH | ARTICLE 13 OF 116 | PRACTICAL SECTION
Automotive Transmissions: Professional Maintenance and Diagnosis
Workshop procedures, tests, symptom interpretation, safety and a technical test with a commented answer key.
Learn to investigate faults without replacing parts by trial and error, carry out inspections suited to each architecture and give correct guidance on transmission maintenance.
9. Diagnosis starts with identifying the system
Before any work, the technician must identify the vehicle model, the engine and the code of the transmission fitted.
Vehicles from the same line may use different transmissions, with different fluids, filters, capacities and procedures.
9.1 Interviewing the customer
Record the information before removing components:
- When did the fault start?
- Does it appear with the vehicle cold, hot or both?
- Does it occur when pulling away, shifting, accelerating or decelerating?
- Is there noise, vibration, a jolt, slipping or delayed engagement?
- Is there a warning on the dashboard?
- Was there a recent fluid change, battery, clutch or other repair?
- What is the maintenance history?
9.2 Not every jolt comes from the transmission
Misfires, irregular engine torque, damaged mounts, loose driveshafts and power supply problems can produce symptoms similar to those of a faulty transmission.
That is why confirming the source of the problem must come before replacing components.
The symptom guides the investigation but does not by itself identify the faulty part. Correct diagnosis combines history, inspection, measurements, electronic data and the tests specified by the manufacturer.
10. Professional diagnostic flowchart
The sequence below organizes the steps of an investigation. Each transmission requires its own test and interpretation procedures.
Diagram 5 — Diagnostic sequence
General flowchart. Specific steps depend on the transmission and the technical documentation.
11. Symptoms and probable causes
| Symptom | Possible causes | First investigation |
|---|---|---|
| Manual hard to engage | Clutch drag, selector, synchronizer or fluid. | Compare engagement with engine running and off; check actuation. |
| Gear grinding | Poor synchronization or incomplete disengagement. | Assess clutch travel and the behavior of the affected gear. |
| Engine revs rise without a matching gain in speed | Clutch or internal element slipping. | Relate engine speed, road speed, load and architecture. |
| Jolt when selecting D or R | Mounts, hydraulic control, adaptation or internal fault. | Inspect mounts, data and fluid condition. |
| Delay before the vehicle moves | Inadequate pressure, internal leak or actuation fault. | Check level, temperature, codes and specified tests. |
| DCT shudder when pulling away | Clutch, engagement control, mounts or adaptation. | Consult clutch and temperature parameters. |
| Noisy CVT | Bearings, pulleys, metal belt, differential or external components. | Locate the source and relate the noise to speed and load. |
| Limp-home mode | Electrical, hydraulic, thermal or plausibility fault. | Read codes and activation conditions. |
12. Transmission fluid: why is the specification critical?
The fluid can perform different functions: lubricate, dissipate heat, transmit hydraulic pressure and control friction between components.
The correct specification is set by the manufacturer. Similar color or viscosity does not guarantee compatibility.
12.1 Manual gearbox fluid
It must meet the lubrication and synchronizer compatibility requirements. Unsuitable oil can impair operation and accelerate wear.
12.2 Automated gearbox fluid
Some systems have the mechanical gearbox fluid and a separate actuation circuit. These circuits must not be confused.
12.3 DCT fluid
The specification depends on the architecture. Certain systems have wet clutches and specific lubrication circuits; others use dry clutches.
12.4 Automatic transmission ATF
Besides lubrication and cooling, ATF can take part in hydraulic control and in the friction characteristics of the internal clutches.
12.5 CVT fluid
In pulley-and-metal-belt transmissions, the fluid is part of the proper operation of the assembly and must meet the exact specification.
Do not replace ATF with CVT fluid, or use generic products without specific approval. Always consult the documentation for the transmission fitted.
13. Fluid level, temperature and condition
The correct level is essential for lubrication, cooling and hydraulic operation. Both too little and too much can cause problems, depending on the design.
In many modern transmissions, the check depends on a specific temperature and an operating sequence defined by the manufacturer.
13.1 What to look for during inspection?
- Leaks.
- Abnormal odor.
- Contamination by water or other fluids.
- Metal particles or friction material.
- History of overheating.
- Changes in behavior during operation.
Fluid color alone is not a conclusive diagnosis. Interpretation must consider the type of fluid and the other signs.
13.2 Change interval
There is no universal interval. Some manufacturers distinguish between normal and severe operating conditions.
The technician must consult the maintenance schedule and record the work done.
14. ATF change: draining and equipment
The fluid in an automatic transmission may be spread between the pan, passages, torque converter and cooler.
That is why a conventional drain does not always remove the whole volume of the system.
14.1 Conventional drain
Removing the accessible fluid by the specified procedure and refilling with the correct quantity and specification.
Depending on the design, the filter, gasket or seals may need replacing.
14.2 Fluid exchange equipment
Specific machines can help renew the fluid in compatible applications.
However, using a machine is not mandatory on every vehicle and does not, by definition, guarantee exact 100% fluid replacement.
14.3 Caution with chemical flushes
Do not use cleaners or additives without specific approval. Unsuitable substances can change friction characteristics and affect seals.
A fluid change is a maintenance operation, not a universal repair. It does not rebuild worn clutches or correct existing electrical or mechanical faults.
15. General fluid maintenance procedure
The following sequence is a study guide. The actual sequence must be taken from the vehicle’s technical manual.
- Identify the transmission code.
- Confirm the fluid specification and quantity.
- Check the temperature and level-check method.
- Inspect for leaks and external condition.
- Lift and support the vehicle correctly.
- Confirm the fill point before draining.
- Collect the used fluid in a suitable container.
- Replace filters and seals when specified.
- Fill with approved fluid using clean tools.
- Perform the specified operating sequence.
- Check the level under the correct condition.
- Check for leaks and correct operation.
- Road test and record the work.
15.1 Cross-contamination
Containers, hoses and tools must be clean. Mixing different fluids can compromise operation.
15.2 Disposal
Used fluid must be disposed of in an environmentally appropriate way through authorized channels, according to applicable legal requirements.
16. Electronic diagnosis with a scan tool
Modern transmissions use sensors and modules to control gears, clutches, pressures and protection strategies.
The scan tool allows relevant information to be checked, but the meaning of each parameter depends on the manufacturer’s architecture and strategy.
16.1 Important data
- Engine speed.
- Transmission input and output speed.
- Gear requested and recognized.
- Fluid temperature.
- Lever position.
- Torque converter status.
- Solenoid commands.
- Actuator position.
- Requested and measured pressures, when available.
- Clutch adaptation status.
- Supply voltage.
16.2 Interpreting fault codes
A code related to a solenoid does not by itself prove the solenoid is faulty. The source may involve the harness, connector, power supply, electronic command or hydraulic conditions.
The correct procedure is to check the technical description of the code and perform the specified tests.
16.3 Freeze-frame data
When available, they help identify the temperature, speed, load and operating condition at the moment the fault was recorded.
16.4 Learning and adaptation
Some transmissions require learning procedures after replacing a clutch, actuator, module or certain internal components.
However, electronic adaptation does not correct mechanical wear or internal leaks.
17. Hydraulic and mechanical tests
In transmissions that allow pressure measurement, this test can help assess the pump, regulators, circuits and actuating elements.
Measurements must only be made with suitable instruments, adapters and procedures.
17.1 Low pressure
May be related to incorrect level, internal leakage, pump wear or regulation faults, among other causes.
17.2 Excessive pressure
May involve electronic control, regulators, solenoids or protection strategies.
17.3 Normal pressure does not rule out every fault
A measurement within the expected range under one condition does not prove there are no problems in every circuit.
Do not perform converter stall tests, full-load tests or actuator activation without an authorized procedure. These tests can generate intense heat, high loads and unexpected movement.
18. Removing and installing the transmission
The transmission is a heavy assembly and may be integrated with mounts, driveshafts, hydraulic systems and electronic components.
18.1 Preparation
- Consult the manufacturer’s removal sequence.
- Use suitable support for the engine and transmission.
- Identify connectors, cables and lines.
- Check lifting points.
- Set aside special tools.
- Identify single-use fasteners.
- Observe torques and tightening sequences.
18.2 Torque converter
In automatic transmissions with a removable converter, correct seating in the internal couplings is essential.
Do not use the bolts to force the engine and transmission together when the components do not fit correctly.
18.3 Manual clutch
Inspect the disc, pressure plate, bearing, flywheel and actuation. Use alignment tools and proper procedures.
18.4 Dual clutch
Some assemblies require positioning tools, clearance measurement and electronic procedures after assembly.
18.5 CVT
Internal disassembly may involve components under mechanical load and requires specific training and tools.
19. P position, parking brake and towing
In many automatic transmissions, the P position engages a mechanical parking lock.
It does not replace the parking brake. The correct sequence must follow the vehicle manual, especially on systems with an electronic parking brake.
On slopes, avoid leaving the vehicle’s weight held only by the transmission lock.
19.1 Towing
The towing method depends on the transmission and drive system. Some architectures can be damaged when certain wheels turn without adequate lubrication.
Consult the manual before moving a broken-down vehicle.
20. Workshop case studies
Symptom: first gear is hard to engage with the engine running, but improves with the engine off.
Investigation: clutch travel, hydraulic or mechanical actuation, disc drag and selector mechanism.
Lesson: investigate disengagement before condemning the synchronizers.
Symptom: selection faults and irregular behavior after the repair.
Investigation: installation, actuator position, sensors and required learning.
Lesson: confirm the initialization procedure before replacing additional parts.
Symptom: vibration when moving off at low speed.
Investigation: clutches, mounts, temperature, adaptation parameters and contamination where applicable.
Lesson: shudder does not necessarily mean a mechatronics fault.
Symptom: the vehicle is slow to start moving.
Investigation: fluid, level, temperature, electronic data, pressure and possible internal leaks.
Lesson: diagnosis must distinguish hydraulic, electronic and mechanical faults.
Symptom: noise that increases with vehicle speed.
Investigation: bearings, differential, tires, pulleys and metal drive belt.
Lesson: locate the source of the noise before blaming the CVT assembly.
21. Maintenance and diagnosis checklist
- □ Transmission identification confirmed.
- □ Complaint recorded.
- □ Maintenance history consulted.
- □ Leaks and external damage inspected.
- □ Mounts and related components checked.
- □ Power supply assessed.
- □ Codes and freeze-frame data recorded.
- □ Fluid specification confirmed.
- □ Level and temperature checked correctly.
- □ Targeted tests performed safely.
- □ Cause of the fault confirmed.
- □ Repairs carried out according to the manufacturer.
- □ Adaptations performed when required.
- □ Road test completed.
- □ Report delivered to the customer.
22. Workshop safety
- Use suitable lifting and support equipment.
- Do not work under a vehicle supported only by a jack.
- Keep your hands away from rotating components.
- Control the risk of burns from hot fluid.
- Follow depressurization procedures.
- Do not activate removed actuators without technical guidance.
- On hybrid and electric vehicles, follow the specific high-voltage procedures.
- Do not road test with faults that compromise safety.
23. How to advise the customer on choosing a transmission?
The best type of transmission depends on the vehicle, the route, the budget and the usage needs.
| Usage profile | What to consider | Guidance |
|---|---|---|
| Heavy city traffic | Comfort and low-speed behavior. | Compare automatics, CVTs and DCTs of specific models. |
| Highway use | Ratios, consumption, noise and performance. | Assess the engine and transmission combination. |
| Load and towing | Approved capacity and thermal control. | Respect the manufacturer’s limits. |
| Low maintenance cost | Parts, history and complexity. | Compare total cost, not just the type of transmission. |
| Sporty driving | Response, control and thermal capacity. | Assess calibration and the specific application. |
24. Technical assessment — 10 questions
Read each question and choose an answer from A to D. Check the commented answer key at the end.
A) To create additional power.
B) To adapt torque and speed to the vehicle’s needs.
C) To replace the brakes.
D) To eliminate all mechanical losses.
A) To increase engine oil pressure.
B) To control cooling.
C) To bring relative speeds closer to make engagement easier.
D) To replace the differential.
A) Electronically controlled actuators.
B) A mandatory torque converter.
C) A metal belt between pulleys.
D) The driver alone.
A) Complete absence of gears.
B) Mandatory use of CVT fluid.
C) Purely hydrodynamic transmission.
D) Two torque paths controlled by separate clutches.
A) To eliminate the differential.
B) To reduce converter slip under suitable conditions.
C) To permanently increase engine speed.
D) To replace the planetary gears.
A) Manually changing external gears.
B) Changing tire pressure.
C) Changing the effective radii of the pulleys.
D) Permanently locking the converter.
A) The method must be compatible and does not necessarily guarantee 100% renewal.
B) It is mandatory on all automatics.
C) It makes the level check unnecessary.
D) It automatically repairs worn clutches.
A) Replace the whole transmission.
B) Clear the code without investigating.
C) Install any solenoid that looks compatible.
D) Diagnose the circuit, power supply, command and hydraulic conditions.
A) Check only the tires.
B) Assess fluid, temperature, electronic data and hydraulic conditions.
C) Always replace the converter.
D) Consider it normal on any vehicle.
A) Ignore electronic procedures.
B) Use CVT fluid in the actuator.
C) Check whether the manufacturer requires learning or calibration.
D) Force engagements until the system adapts.
25. Answer key with comments
1. B — Adapt torque and speed.
The transmission changes the mechanical ratios but does not create power.
2. C — Bring relative speeds closer.
The synchronizer makes engaging the selection components easier.
3. A — Electronically controlled actuators.
The system automates clutch actuation and ratio selection.
4. D — Two torque paths.
The dual clutch allows ratios to be prepared on different paths.
5. B — Reduce slip.
The lock-up reduces hydrodynamic losses under specified conditions.
6. C — Changing the effective radii.
Changing the contact on the pulleys alters the ratio continuously.
7. A — Compatible method, no universal 100% guarantee.
Renewal depends on the equipment, circuit and procedure.
8. D — Diagnose the system.
The code may involve the solenoid, harness, power supply or control.
9. B — Assess fluid, data and hydraulics.
Delayed engagement can have multiple causes.
10. C — Check learning or calibration.
Some transmissions require electronic procedures after work.
26. Review summary
- The transmission adapts torque and speed.
- The manual uses a clutch and synchronizers.
- The automated gearbox uses actuators to operate a mechanical gearbox.
- The DCT has two torque paths.
- The planetary automatic uses friction elements and hydraulic control.
- The converter may have a lock-up clutch.
- The pulley CVT continuously changes its effective radii.
- Not every CVT uses a metal belt.
- Fluids are not universally interchangeable.
- No fluid change method is mandatory for every vehicle.
- Fault codes guide tests, not automatic replacements.
- Electronic adaptation does not repair mechanical wear.
- Diagnosis must end with validation of operation.
27. Technical references for the workshop
For real jobs, use the vehicle and transmission manufacturer’s documentation, including:
- Exact identification of the gearbox.
- Fluid specification, volume and level procedure.
- Temperatures and operating conditions.
- Torques and tightening sequences.
- Removal and installation procedures.
- Authorized electronic and hydraulic tests.
- Learning and calibration procedures.
- Applicable technical bulletins and updates.
Technical training, well-founded diagnosis and excellence in automotive mechanics.
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