Overview of how and why GM Transmissions Fail
If you have a GM Truck or Van with a 6-speed transmission, built after 2006, these issues are likely to affect your truck. If you tow/haul frequently, or need to ensure as little down-time in your truck as possible, there are pre-emptive maintenance repairs that can be undertaken to prevent transmission failure.
This article focuses on what is happening, why, and touches on how National Transmission has developed a bulletproof fix for this issue.
Not sure if you have this transmission? There’s a list at the bottom of this page.
What are the symptoms of this failure?
- If the transmission is failing:
- It might skip gears
- It could be slow to engage into drive
- It is likely to start slipping
- A smaller repair bill
- If the transmission has likely failed (red alert!):
- The truck will not move – Sometimes called P-N-N-N-N-N (Park-Neutral-Neutral….)
- You are likely to smell burnt clutch material
- A larger repair bill
Non-Technical Summary
If you’re not overly ‘mechanical’ but you think you might be impacted by this issue. Here is a summary just for you.
The good news is that these transmissions have come through our shop 1000s of times, so we are able to fix the root causes before they cause catastrophic failure.
Watch the full 6L80 and 6L90 Transmission Teardown and Repair Video
(Or read more about it below the video.)
What is happening to the transmission and how is it starting to fail?
Basically, General Motors had decided to increase the manufacturing efficiency by cutting corners on welding, and by using too thin metals, which ultimately cause rotational balance issues, which lead to premature wear of the clutch – the clutch wear produces metal shavings, which get caught in the oil pump. The additional friction inside the pump from oil shavings cause it to fail, leading to a lack of lubrication inside the transmission, which breaks the whole system.
How do you know when the transmission has failed?
You’ll notice the moment of catastrophic failure because the truck will suddenly not move under its power. That said, there are warning signs to be aware of including slipping, missing gears, shuddering, vibrations, weird smells and loud clunking noises.
The National Transmission solution to fixing GM 6L80 and 6L90 Transmissions?
Thicker steel and better welds. We install a “billet” base to the Torque Converter, which is machined (not welded), which prevents warping and additional friction on the clutch. We also supplement the fusion welds in the the drum with spot-welds, which are then machined flat to maintain rotational and harmonic balancing, while also greatly increasing the structural strength between the two pieces.
Right to repair!
National Transmission works with local fabricators to create replacement parts. We believe that you should only replace the entire thing if you have no other choice, because a brand new OEM transmission will likely have a similar issue.
We can solve this for you at the root, so you’ll get a lot more use out of your vehicle without throwing money at the problem.
FAQ
Does my Truck have a 6L80?
Yes, if you have one of the following
Cadillac Escalade ESV, 2007-2015
Cadillac Escalade EXT, 2007-2013
Cadillac Escalade, 2007-2015
Cadillac STS-V, 2006-2009
Chevrolet Avalanche, 2009-2013
Chevrolet Silverado 1500 5.3 (ext. & crew cab), 6.2, 2009-2013
Chevrolet Silverado 1500 5.3 (reg. cab), 2010-2013
Chevrolet Silverado, (T1XX) 2019-2021
Chevrolet Silverado2014-2019 (K2XX)
Chevrolet Suburban 1500, 2009-2020
Chevrolet Suburban 2500 (6L90), 2008-2013
Chevrolet Tahoe, 2009-2020
GMC Sierra 1500 5.3 (ext. & crew cab), 6.2, 2009-2013
GMC Sierra 1500 5.3 (reg. cab), 2010-2013
GMC Sierra 1500, 2014-2019 (K2XX)
GMC Sierra 1500, (T1XX) 2019-2021
GMC Sierra Denali, 2007-2013
GMC Yukon Denali, 2007-2015
GMC Yukon XL, 2009-2020
GMC Yukon, 2009-2020
Hummer H2, 2008-2009
Does my Truck have a 6L90?
Yes, if you have one of the following
Chevrolet Express 2500-3500 (6L90-E), 2010-present
Chevrolet Silverado 2500HD/3500 HD 6.0 (6L90), 2007-2014
Chevrolet Silverado 2500HD/3500 HD 6.0 (6L90), 2015-2019
Chevrolet Silverado 2500HD/3500 HD 6.6 L8T (6L90), 2020-present
Chevrolet Suburban 2500 (6L90), 2008-2013
GMC Savana 2500-3500 (6L90-E), 2010-present
GMC Sierra 2500HD/3500HD 6.0 (6L90), 2007-2014
GMC Sierra 2500HD/3500HD 6.0 (6L90), 2015-2019
GMC Sierra 2500HD/3500HD 6.6 L8T (6L90), 2020-present
Which other GM vehicles have this transmission?
A few of the high-power LS sports cars, including:
Chevrolet Corvette, 2006-2013
Chevrolet Camaro, 2010-2015
Chevrolet Camaro ZL1 (6L90), 2012-2015
