GM uses both 6L80 6-speed and 8L90 8-speed in modern trucks. They look similar but have important differences. Here's the comparison.
Quick overview
6L80 (2006-present):
- 6-speed automatic
- Found in Silverado, Sierra, Tahoe, Yukon
- ~470 ft-lb stock capacity
- Hydramatic 6L80
6L90 (2007-present):
- HD version of 6L80
- 6-speed automatic
- Heavier internals
- ~580 ft-lb stock capacity
8L90 (2015-present):
- 8-speed automatic
- HD applications
- Stronger components
- ~600 ft-lb stock capacity
8L45 (2015-present):
- Lighter-duty 8-speed
- Smaller package
Read our 6L80 vs 4L60E comparison
Read our 6L80 mechatronics rebuild
Gear ratios
6L80:
- 1st: 4.03
- 2nd: 2.36
- 3rd: 1.53
- 4th: 1.15
- 5th: 0.85
- 6th: 0.67
8L90:
- 1st: 4.56
- 2nd: 2.97
- 3rd: 2.08
- 4th: 1.69
- 5th: 1.27
- 6th: 1.00
- 7th: 0.85
- 8th: 0.65
Result:
- 8L90 has lower 1st gear (better acceleration)
- 8L90 has wider gear spread
- 8L90 generally more efficient at cruise
Strength and capacity
6L80:
- Stock: ~470 ft-lb
- With HD upgrades: 700+ ft-lb
- Read our 6L80 input drum failure guide
6L90:
- Stock: ~580 ft-lb
- With HD upgrades: 850+ ft-lb
8L90:
- Stock: ~600 ft-lb
- With HD upgrades: 900+ ft-lb
Common failures
6L80 famous failures:
- TCC PWM shudder (45-65 mph)
- Wave plate cracking
- Input drum failure
- Read our 6L80 shudder fix guide
8L90 famous failures:
- TCC shudder (same as 6L80)
- Hard shifts at lockup
- Mechatronics wear
- Read our 6L80 mechatronics rebuild (similar issues)
Applications
6L80:
- 2007-2013 Silverado/Sierra 1500 (5.3L/6.2L)
- 2007-2014 Tahoe/Yukon/Suburban
- Camaro (early 6-speed era)
- Corvette (early 6-speed era)
6L90:
- 2007-2013 Silverado/Sierra 2500HD (gas)
- HD passenger applications
- Express vans
8L90:
- 2015-present Silverado/Sierra 1500 (5.3L/6.2L)
- 2015-present Tahoe/Yukon
- 2014+ Corvette Stingray
- ZL1 Camaro
8L45:
- Lighter-duty applications
- Mid-size Colorado/Canyon
Identification
By VIN:
- 8th character of VIN identifies trans family
- Verify on application-specific basis
By year and engine:
- 2006-2014 with 5.3L/6.2L = 6L80
- 2015+ with 5.3L/6.2L = 8L90
By transmission case:
- 6L80: shorter case
- 8L90: longer case, two extra gears means more length
Rebuild costs
6L80:
- DIY: $800-1,400
- Shop: $2,500-4,000
- Read our 6L80 rebuild cost guide
6L90:
- DIY: $900-1,500
- Shop: $2,800-4,500
- Slightly more than 6L80 due to HD parts
8L90:
- DIY: $1,000-1,800
- Shop: $3,000-5,000
- Newer trans, parts more expensive
Which to upgrade vs replace
Truck with 6L80, tow rig usage:
- Rebuild with HD parts
- Sonnax billet input drum
- Updated TCC PWM
- Read our best 6L80 rebuild kit
Truck with 8L90, daily driver:
- Reman often more cost-effective than rebuild
- Mechatronics is expensive item
Truck with 8L90, HD use:
- HD rebuild parts available
- Sonnax solutions emerging
- Plan for premium fluid, aux cooler
Maintenance considerations
Fluid:
- 6L80: Dexron VI
- 6L90: Dexron VI
- 8L90: Dexron VI HP (specific to 8-speed)
- Don't mix
- Read our transmission fluid types guide
Filter:
- Different filter elements between 6L80 and 8L90
- Read our transmission filter guide
Cooler:
- Both benefit from aux cooler for HD use
- Read our transmission cooler installation guide
Performance considerations
6L80 for HP builds:
- HD parts widely available
- Sonnax solutions established
- Aftermarket support strong
8L90 for HP builds:
- Aftermarket developing
- Stock capacity higher
- Some HD parts not yet available
- Performance tuning more limited
Need 6L80 or 8L90 parts? Shop our complete catalog. Master rebuild kits, Sonnax HD upgrades, mechatronics components. Free shipping over $70.
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