Introduction
The GM 8L90 (8-speed automatic transmission) was introduced by General Motors in 2014 as a high-performance successor to the 6L80. Designed for rear-wheel-drive (RWD) and all-wheel-drive (AWD) applications, the 8L90 aimed to improve fuel efficiency, enhance performance, and provide seamless shifting. Despite its technological advancements, the transmission has faced notable reliability issues.
Technical Innovations of the 8L90
The 8L90 was engineered to handle high-torque applications, making it a common choice for GM’s high-performance and full-size vehicles. Some of its key technical innovations include:
1. Improved Gear Spread & Fuel Efficiency
- The 8-speed design allowed for a 7.0 overall gear ratio, enabling better acceleration and highway fuel efficiency.
- A steep first gear (4.56:1) improved low-speed torque, while the 0.65:1 top gear helped with fuel economy.
2. Lightweight & Compact Design
- Built using an aluminum case and lightweight internal components, the 8L90 weighed only 8 pounds morethan its predecessor (6L80) despite having two extra gears.
- It featured an integrated bell housing for better structural rigidity.
3. Faster Shift Times
- The new torque converter and optimized clutch-to-clutch shifting allowed up to 40% quicker shiftscompared to the 6L80.
- Used adaptive shift control and direct Active Fuel Management (AFM) integration to enhance responsiveness.
4. Advanced Hydraulics & Cooling
- Featured dual internal transmission fluid pumps, ensuring better lubrication and cooling.
- Utilized a thermally controlled transmission oil pump that optimized fluid pressure based on driving conditions.
Common Issues & Faults of the GM 8L90
While the 8L90 introduced several improvements, it has been plagued by reliability issues, leading to complaints and lawsuits. Some of the most common problems include:
1. Torque Converter Shudder (Shuddering/Vibration)
- One of the biggest complaints with the 8L90 is the shuddering sensation during acceleration or cruising.
- Caused by torque converter clutch (TCC) failure, leading to fluid degradation and poor lockup engagement.
- GM attempted to resolve this with multiple TSBs (Technical Service Bulletins) and updated transmission fluid formulas.
2. Harsh or Delayed Shifting (“Slipping” or “Clunking”)
- Many owners report jerky downshifts or hard upshifts, especially at low speeds.
- This is often due to valve body wear, solenoid malfunctions, or clutch pack issues.
3. Transmission Overheating & Fluid Issues
- The 8L90’s complex cooling system has had failures, leading to overheating and fluid contamination.
- The original Dexron HP transmission fluid was later replaced with Mobil 1 Synthetic LV ATF HP to reduce shudder.
4. Internal Component Wear & Metal Contamination
- Premature clutch pack wear leads to internal metal shavings, which clog the valve body and result in gear slipping or no reverse/drive engagement.
List of Vehicles Equipped with the GM 8L90
The 8L90 was used in several high-performance Chevrolet, Cadillac, and GMC vehicles. Below is a list of cars and trucks equipped with this transmission:
Chevrolet
- Corvette C7 (2015-2019) – Z06 & Grand Sport models
- Camaro (2016-2019) – SS, ZL1
- Silverado 1500 (2015-2018) – 5.3L & 6.2L V8 models
GMC
- Sierra 1500 (2015-2018) – 6.2L V8 models
- Yukon & Yukon XL (2015-2018) – Denali models
Cadillac
- CTS-V (2016-2019)
- Escalade (2015-2018)
Conclusion
The GM 8L90 was a significant step forward in automatic transmission technology, offering faster shifts and improved fuel efficiency. However, its torque converter issues, shifting problems, and overheating concerns have tarnished its reputation. While GM has made improvements over time, many owners have faced expensive repairs or replacements.
If you’re considering buying a used vehicle with an 8L90 transmission, make sure to check service records for fluid updates and transmission software patches to mitigate known issues. Action Transmission can rebuild, replace, or repair the 8L90 transmission.
