Boxes of the 6T30 series are built to work with small-displacement, low-power engines. They appear in models such as the Chevrolet Aveo, Cruze, Orlando, Cobalt, and Lacetti, and in Daewoo Gentra as well. The 6T40 units are designed for heavier, more powerful vehicles, including Chevrolet Captiva, Cruze, and Lacetti. The 6T45E is installed in front-wheel drive and all-wheel drive cars up to 3.2 liters, for example the Opel Antara.
The first digit in the designation shows the number of gears. The letter T indicates that these gearboxes are paired with transversely mounted engines. The numbers 30, 40, and 45 specify their torque class.
Regardless of the exact model they’re paired with, owners tend to face similar issues.
Overheating of the working fluid
In hot summer conditions, in city traffic, and under heavy-load driving, the transmission fluid can exceed 100 C. When automatic transmission fluid overheats, its performance declines quickly. To reduce this risk, keeping the air conditioning heat exchanger and the engine radiator clean is helpful; they can be washed by the owner if needed.
For transmissions that experience frequent heavy loads, adding an auxiliary radiator is worth considering. A thermostat is also useful to prevent the fluid from getting excessively cold in winter. Installing such a kit can cost up to 15 thousand rubles.
Kits are available to add a radiator for automatic transmissions, though the thermostat is not included.
The thermostat, set around 75-85 C, directs fluid flow through the additional radiator.
Complex design
Chain drives are uncommon in traditional hydromechanical automatics. Most transverse automatics rely on cylindrical gears for power transfer. In the GM box, torque from the planetary sets to the differential is transmitted by a multi-row chain, a design that wears quickly due to numerous joints. Debris from wear travels with the fluid and can disrupt other components.
Energy chain transmission remains a rare feature in automatic transmission design.
Malicious unification
To cut production costs, designers unified gearboxes for engines with significantly different power outputs. In compact cars, this can lead to a heavier box with ample safety margins, while in larger cars the endurance may fall short. The typical mileage before overhaul ranges around 120-150 thousand kilometers, which is insufficient for a hydromechanical machine in some cases.
Many elements in a number of gearboxes are interchangeable, reducing manufacturer costs but not necessarily lowering repair costs for consumers.
Premature pressure loss
Higher vibration from transmitting maximum torque can degrade shaft sleeves. Worn bushings allow ATF to escape from working cavities, reducing pump performance. The electronic control system then prompts solenoids to open further, causing clutch slip. Debris in the fluid can clog the valve body and impair operation.
Problems with the valve body
This design has undergone several modernizations, yet issues persist. When operating with a superheated liquid containing ferrous particles, shaft speed sensors based on the Hall effect can misread due to metallic debris sticking to them. The issue often starts with gears from fourth through sixth, and can escalate.
A practical tip is to change the fluid and filter more frequently to prolong the life of the transmission.
Here are additional precautions for maintenance and repair of these transmissions.
Check the torque converter
When servicing 6T30, 6T40, or 6T45 transmissions, attention should be paid to the friction discs inside the torque converter. Malfunctions can cause excessive chip contamination in the fluid, which rapidly wears the clutches.
During dismantling, the torque converter remains attached to the engine and still requires diagnosis and possibly repair.
Avoid aggressive tuning
All boxes in this family have limited torque margins. They perform best when driven smoothly and within reasonable limits. Forcing the engine with these automatics is discouraged, as it can lead to early repairs for the transmission and potentially the engine as well.
These insights come from ongoing automotive testing and field experience, drawn from automotive engineering reports and data from vehicle databases and service manuals.