The 8L90 is the eight-speed automatic GM introduced for the 2015 model year to follow the six-speed 6L80 and 6L90 in its performance cars and many full-size trucks and SUVs. It adds two gears, a deeper first and a taller top gear, in a package designed to fit roughly the space the six-speed used. The 6L80 has a longer track record and simpler service; the 8L90 is known for torque converter shudder and harsh shift complaints, many of them addressed by a fluid change and software updates.
6L80 vs 8L90 at a glance
| 6L80 | 8L90 | |
|---|---|---|
| Gears | 6 | 8 |
| Gear ratios | 4.03 / 2.36 / 1.53 / 1.15 / 0.85 / 0.67 | 4.56 / 2.97 / 2.08 / 1.69 / 1.27 / 1.00 / 0.85 / 0.65 |
| Introduced | 2006 | 2015 model year |
| Typical vehicles | Silverado, Sierra, Tahoe, Camaro, Corvette | Corvette, Camaro SS and ZL1, 6.2 Silverado and Sierra, Escalade |
| Fluid | Dexron VI | The fluid GM currently specifies, which changed during its run |
Which is better?
For towing and highway economy the 8L90’s closer steps and taller top gear help, and it suits high-output engines. The 6L80 is simpler, widely understood and well supported in swaps. Reliability depends heavily on maintenance and whether known fixes have been applied; see 8L90 problems and 6L80E problems.
The 8L90 shudder and the fluid change
Many 8L90 shudder complaints were traced to the torque converter clutch and the original fluid. GM issued service bulletins that include a fluid flush with an updated fluid, and some trucks also needed a converter. If you are shopping for an 8L90 vehicle, ask whether the fluid service and updates were done.
How to tell them apart
The model year and option codes on the vehicle’s service parts label settle it, and the transmission tag confirms it. The 8L90 has a different pan and electrical connector, so the two are not interchangeable without changes to wiring and programming.
Swapping
Both are used in swaps, and both need a compatible controller and programming. The 6L80 is the more common, simpler choice; see 6L80 swap and LS swap transmission options.
What came next
GM moved many trucks to the ten-speed 10L80; see 8L90 vs 10L80 and 6L80 vs 6L90.
Replacement units we list
- RoadReady Chevy 6L80E: $2,699.00
- StreetMonster Chevy 6L80E: $3,399.00
- RoadReady Chevy 8L90: $4,399.00
- StreetMonster Chevy 8L90E: $3,999.00
Each includes a torque converter. Browse 6L80E and 8L90 transmissions.
More guides: how long a 6L80 lasts · how much power a 6L80 can handle · how long an 8L90 lasts.
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