Notes When Repairing - Replacing Car Gearboxes Effectively

Note on repairing/replacing car gearbox
Latest update date: February 07, 03

Car gearbox is an important part of the vehicle's transmission system, which functions to transmit power from the engine to the wheels, while adjusting the transmission ratio to suit the vehicle's speed and load.

With the development of technology, the types of gearboxes are increasingly diverse and complex, from traditional manual gearboxes to modern automatic gearboxes such as AT, CVT and DCT. However, after a period of use, the gearbox can encounter many problems such as unusual noise, difficulty shifting gears, oil leaks or electronic errors.

Understanding the signs of damage, when to replace them, and the correct repair process will help car owners protect their beloved car's "second heart," while saving costs and ensuring safety on the road.

According to the SAE Technical Documentation (USA), regular maintenance according to the manufacturer's specifications can help prevent 85% of gearbox failures. Using genuine spare parts also helps reduce the failure rate by 64% compared to replacement parts.

This article will provide you with detailed information about gearbox classification, signs of damage, repair procedures and important notes to help you make the best decision.

Note on repairing/replacing car gearbox
Car transmission repair/replacement: things to know

What types of car gearboxes are there?

There are four main types of transmissions: manual transmission, automatic transmission, continuously variable transmission, and dual-clutch transmission.

1. Manual Transmission

Manual transmission, also known as manual transmission, is a traditional type of car transmission in which the driver must manually control the gear changes using the gear lever and clutch pedal. The main features of a manual transmission include:

  • Simple structure, easy to maintain and repair.
  • Low production and maintenance costs.
  • More fuel efficient than automatic transmission.
  • For a sporty driving feel, better vehicle control.
  • Requires more complex control skills.
Manual transmission (Manual Transmission)
Manual transmission (Manual Transmission)

2. Automatic Transmission

An automatic transmission is a type of car transmission that automatically changes gear ratios without direct intervention from the driver. This allows the vehicle to automatically adjust speed and torque based on driving conditions and load. Highlights:

  • Smooth operation, easy to use.
  • Suitable for urban traffic conditions.
  • Complex structure, high production and maintenance costs.
  • More fuel consumption than manual transmission.
  • Response time when accelerating is slower.
Automatic Transmission
Automatic Transmission

3. Continuously Variable Transmission (CVT)

Continuously variable transmission is a unique type of automatic transmission, different from the traditional automatic transmission (AT) or manual transmission. The highlight of CVT is the ability to change the transmission ratio continuously, regardless of specific gears. Characteristics of CVT transmission:

  • Extremely smooth gear shifting, no jerking feeling.
  • Good fuel economy at steady speed.
  • Simpler construction than conventional automatic transmission.
  • Acceleration is not as strong as other types of gearboxes.
  • High production cost, long-term durability not proven.
Continuously Variable Transmission (CVT)
Continuously Variable Transmission (CVT)

4. Dual Clutch Transmission (DCT)

Dual-clutch transmission is an advanced type of automatic transmission that combines the advantages of manual transmission and traditional automatic transmission. It is designed to provide fast, smooth shifting and high performance. Main features:

  • Extremely fast shifting, virtually lag-free.
  • More fuel efficient than conventional automatic transmission.
  • For a sporty, powerful driving feel.
  • Complex structure, high production and maintenance costs.
  • Reliability problems may occur if not properly maintained.
Dual Clutch Transmission (DCT)
Dual Clutch Transmission (DCT)

What signs help identify a problem with a car's gearbox?

Strange noises when shifting gears, difficulty or delay when shifting gears, shaking when accelerating/decelerating, transmission fluid leaks, and transmission fluid warning light are 5 warning signs that your car's transmission is having problems.

1. Strange noise (squealing, rattling, howling) when shifting gears

When your transmission makes unusual noises such as screeching, rattling or howling, especially when shifting gears, it could be a sign of problems such as:

  • Gear wear or damage.
  • Lack of lubrication.
  • Bearing or bearing failure.

In this case, check and add the transmission fluid if needed. If the problem persists, take the car to a garage for a more thorough check.

2. Difficulty or delay in shifting gears

If you have difficulty shifting gears or feel a delay when shifting, it could be due to:

  • The control valve system is damaged.
  • Valve piston stuck or stiff.
  • Solenoid fault.
  • The gasket is stiff or damaged.

To fix, check and replace damaged parts such as valves, solenoids or gaskets.

3. Shaking when accelerating or decelerating

Shaking when accelerating or decelerating can be caused by:

  • Loss of clutch pressure.
  • Valve wall scratches.
  • Piston leak.
  • The digital control box is broken.

The solution depends on the specific cause, may require replacing the valve, checking the wiring or replacing the TCM control box.

4. Gearbox oil leakage

Leaking transmission fluid is one of the most common signs of a failing transmission. It is often caused by:

  • Rubber gasket is aging.
  • Seal is warped or misaligned.
  • Damage due to collision or lack of maintenance.

To fix, check and replace damaged gaskets and seals.

5. Transmission fault light is on on the dashboard

When the transmission fault light comes on, it is usually related to problems with:

  • Gear oil temperature.
  • Oil pressure.
  • Oil level in gearbox.
  • Sensor error.

In this case, it is recommended to use specialized diagnostic equipment to accurately determine the cause and take appropriate corrective measures.

When to replace car gearbox?

Car gearboxes need to be replaced when they are severely damaged after an accident or flooding, the repair cost is high (>70% of the replacement value), the gearbox is too old and needs to be upgraded to increase operating efficiency.

When to replace car gearbox
When to replace car gearbox?
  • Severe damage after accident or flooding

When the vehicle is involved in a serious accident or is submerged in deep water, the transmission may be irreparably damaged. In this case, a complete transmission replacement is necessary to ensure the safety and performance of the vehicle.

  • Repair costs exceed 70% of replacement value

If the estimated cost of repairing a transmission exceeds 70% of the value of a new transmission, a complete replacement will be the more economical option in the long run. This ensures better reliability and performance than repairing a transmission that is too old or badly damaged.

  • The gearbox is too old (over 15 years old) and there are no spare parts available.

For older vehicles (over 15 years old), finding replacement parts for the transmission can be difficult and expensive. In this case, replacing it with a new or remanufactured transmission is the optimal solution.

  • Upgrade gearbox for improved performance

Some car owners decide to upgrade their transmission to improve performance, fuel economy, or load capacity. For example, switching from a manual to an automatic transmission or upgrading to a transmission with more gears.

What is the process of repairing car gearbox?

The standard car gearbox repair process includes the following 5 basic steps:

Step 1 – Check and diagnose with specialized equipment

Use modern diagnostic equipment such as OBD-II scanners to read fault codes and pinpoint the exact problem with your transmission. This saves time and increases accuracy in determining the cause of the failure.

Step 2 – Disassemble the gearbox and inspect the parts

Once the problem is identified, the technician will remove the transmission from the vehicle and inspect each part. This process includes:

  • Remove the transmission from the vehicle.
  • Clean the parts.
  • Check the size and wear of parts such as gears, shafts, bearings, and clutches.

Step 3 – Replace damaged parts with genuine spare parts

Based on the inspection results, the damaged parts will be replaced with genuine spare parts or high quality equivalents. This ensures the durability and performance of the gearbox after repair.

Step 4 – Clean and reassemble the gearbox according to the correct procedure

After replacing the necessary parts, the gearbox will be thoroughly cleaned and reassembled according to the manufacturer's procedures. This includes:

  • Assemble the parts in the correct order.
  • Tighten the bolts to the specified torque.
  • Lubricate necessary parts.

Step 5 – Check and calibrate after assembly

Once assembly is complete, the gearbox is thoroughly tested on a dedicated test bench to ensure smooth and faultless operation. Parameters such as oil pressure and gear shifting smoothness are checked and calibrated if necessary.

What to note when repairing and replacing car gearboxes?

6 important notes when repairing/replacing a car's gearbox include: choosing the right reputable garage, carefully checking the details before repairing, using genuine or equivalent spare parts, ensuring proper installation, changing the gearbox oil periodically and requesting a warranty after replacement.

1. Choose a reputable, experienced garage

Choosing the right repair garage is the most important factor to ensure the quality of service. Reputable garages often have a team of skilled technicians and modern equipment, helping to diagnose and repair the gearbox accurately.

2. Carefully check the details before repairing or replacing.

Before proceeding with any repair or replacement, a thorough inspection of the transmission components is required. This will help pinpoint the exact cause of the failure and avoid unnecessary replacement. Components such as gears, clutches, and electronic components should be carefully inspected.

3. Use genuine spare parts or equivalent

When replacing damaged parts, it is important to use genuine spare parts or spare parts of equivalent quality. This not only ensures durability but also helps maintain the performance of the gearbox after repair.

4. Ensure proper installation

Transmission installation needs to be done properly to ensure everything runs smoothly. Technicians need to follow the manufacturer's instructions on how to assemble and adjust the transmission.

5. Make sure to change the transmission oil with the right type and at the right time.

Transmission fluid plays an important role in lubricating and cooling internal components. Using the wrong type of fluid or not changing it regularly can lead to serious damage. Vehicle owners should consult the manufacturer's instructions for the appropriate type of fluid and when to change it.

6. Warranty claim after replacement

After completing the repair or replacement of the transmission, the car owner should request a warranty for the services performed. The warranty is not only a commitment to the quality of the service but also helps the car owner feel more secure during use.

FAQ – Frequently Asked Questions

1. What is car gearbox overhaul? When is a gearbox overhaul needed?

Automotive gearbox overhaul is the process of repairing all or a large part of the transmission to restore its performance. Vehicle owners often need to overhaul the transmission when it has suffered serious damage, the repair cost is high, or when the vehicle has been used for many years without proper maintenance.

2. How to distinguish between a damaged car gearbox due to mechanical failure and an electronic failure?

To differentiate between mechanical and electronic faults, car owners can check for fault codes using an OBD-II diagnostic tool. If there is a fault code related to a sensor or electronic control system, it is an electronic fault. On the other hand, if there are signs such as strange noises or difficulty shifting gears without a fault code, it may be a mechanical fault.

Read the article now: Instructions How to check, diagnose, read and fix errors using a diagnostic machine fast, accurate

3. What factors affect the life of an automatic car transmission?

The lifespan of an automatic car transmission depends on many factors such as:

4. Should I buy a used car gearbox to replace it?

Buying a used transmission can save money, but it also comes with risks. If you decide to buy one, you should ask for documentation proving the origin and condition of the transmission, and have it thoroughly inspected before installation.

5. Can I change the transmission oil at home?

Self-employment change transmission oil at home is possible but requires the right knowledge and tools. Vehicle owners need to ensure that they use the correct type of oil and follow the oil change procedure as recommended by the manufacturer to avoid damaging the system.

6. Which garage repairs/replaces reputable car gearboxes in Ho Chi Minh City?

Thanh Phong Auto Thanh Phong Auto is proud to be a trusted address for auto gearbox repair and replacement services in Ho Chi Minh City, providing customers with a professional experience and absolute peace of mind. With a team of skilled, well-trained and experienced technicians, Thanh Phong Auto is committed to accurately diagnosing the condition of the gearbox and providing the most optimal solution.

Outstanding advantages at Thanh Phong Auto:

  • Modern equipment: Thanh Phong Auto invests heavily in the most advanced gearbox diagnostic and repair equipment, helping to detect and handle problems quickly and effectively.
  • Genuine spare parts: The center is committed to using 100% genuine spare parts or equivalent, ensuring quality and durability for the gearbox after repair.
  • Professional process: The gearbox repair and replacement process is carried out according to strict, clear and transparent standards.
  • Considerate warranty policy: Thanh Phong Auto provides long-term warranty policy, bringing absolute peace of mind to customers.
  • Dedicated consulting team: The team of consultants is always ready to listen, answer questions and support customers in choosing the appropriate repair plan.
  • Convenient location: With 7 large branches in District 7 and Nha Be, Thanh Phong Auto brings convenience to customers in traveling and using services.

Coming to Thanh Phong Auto, customers will experience high quality, fast and efficient auto gearbox repair and replacement services.

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