By Dave Riccio, ASE Certified Technician, Owner of Tri-City Transmission & Auto Repair, Co-Founder of Bumper to Bumper Radio
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| Dave Riccio, Owner/Technician |
CASE STUDY: 2018 Chevrolet Colorado Transmission Issues 8L45 / 8L90 - Tri-City Transmission and Auto Repair Order Number #3010840 - #19-NA-018
Shake and/or Shudder During Light Throttle Acceleration Between 25 and 80 mph
This Case Study Would Also Apply to Similar Vehicles w/the Same Transmission: Chevrolet Silverado, Chevrolet Colorado, GMC Sierra, GMC Yukon, GMC Canyon, Cadillac Escalade, Cadillac ATS, Cadillac CT6 & Cadillac CTS
Case Study Details
This customer fell subject to inexperience. This inexperience shows up most when it comes to the need for transmission diagnosis. It is our experience that most in the automotive repair industry don't have much understanding of transmissions and how they work. This is even though they think they do. The symptoms that this customer had are oftentimes misdiagnosed. Technicians can incorrectly identify them as a misfire and then attempt to make repairs to the fuel and ignition systems. In this case, this customer went to two shops where both took his money and he left with the same issues. Neither of the shops he went to took a road test with him to understand his symptoms. An unfortunate all too common misstep by consumers and shops alike. His frustration was significant when he reached out to us at Tri-City Transmission and Auto Repair. After all, his truck only had 77,438 miles on it and why he was dealing with this issue.
When he dropped the vehicle off, our technician went for a five-mile road test with the customer to verify the symptoms he was experiencing. The symptoms were not totally consistent, so it took a smooth road and know how to make the symptom happen. From there, our technician checked all the basics that often get passed over in the novice diagnostic process. Battery, alternator, computer logic, software calibration, fluid condition, transmission operating temperatures and so on. After the road test with the customer, from his experience, our technician had a hunch he was looking at torque converter clutch chatter. His next step was with a scanner. He set up a graph on the scanner to compare engine RPM and transmission input shaft speed. This is a sure way to see torque converter clutch slip RPM in the live scanner data. This was not a code diagnosis, and usually isn’t, as this vehicle had no diagnostic trouble codes set. After setting up the scanner, our technician then headed out on an additional road test while reading scanner live data. He experienced a direct correlation between the graphing on the scanner and the seat of the pants feel driving the truck. Graph data is included in the attached PDF.
Our preliminary diagnosis: Failing torque converter clutch, failing transmission fluid, or both. The next step of diagnostic and repair is either to perform the specific Mobil 1 transmission fluid service developed for this issue or remove the transmission, replace the torque converter and reinstall with new Mobile 1 fluid now designed for this transmission.
Feedback from GM dealerships has been that servicing them doesn’t work. Our experience is that it does in fact work. We realize that GM technicians on flat rate pay are going to favor the guaranteed fix of the transmission replacement. They make more money and skip the hassle of a service that may or may not work. General Motors has really made it a pain in the ass for technicians to do the service first. Another reason we have seen technicians condemn a perfectly good transmission.
In this case, we decided this Chevrolet Colorado being a light truck, and low miles that a service would more than likely work. Guess what, it did! We have done several other different GM vehicles for this same issue and they all have worked with a fluid change. This includes GMC trucks and SUVs, Cadillac SUVs and Cars and Corvettes. Vehicle list provided below. Scanner data cleans right up after the service and the symptom is alleviated. No need for the expense of a different torque converter or in some cases, transmission as the dealers seem to be recommending without any due diligence in the diagnostic process.
Transmission Background
General Motors is not a new player when it comes to torque converter clutch chatter and torque converter clutch failure. The issue has been going on for General Motors for years since their introduction of the 4L60E transmission in the early 90’s. Even though GM has been a pioneer in transmission design and manufacturing, specifically the lock up torque converter from the 80’s - they have had a myriad of issues that seem to get worse with each iteration of their transmissions. The TH700R4 / 4L60 had trouble with its P1870 codes for slipping converter clutch, its predecessor the 6L80 / 6L90 had a much bigger issue with torque converters crashing in the early life of the vehicle. This newest longitudinal car and truck transmission from GM, model number 8L45 and 8L90 is looking to be the cherry on top of GM’s torque converter clutch lock up control and design issues.
This newest model GM Transmission the 8L45 and 8L90 is littered with technical service bulletins with more expected to come. We have attached one of those here.
Why does our industry see torque converter clutch failures?
Most late model transmissions begin failing at the torque converter clutch. If not caught soon enough, they wipe out the whole transmission. So why is this a struggle for auto manufacturers? Fuel Efficiency, Fuel Efficiency, Fuel Efficiency and ride quality for the passengers. As a result, auto manufacturers have way overcontrolled the torque converter clutch. Torque converter clutches typically only used to come on with the final gears. However, that was inefficient for fuel consumption. So late model torque converter clutches are turned on often in 2nd gear and are modulated on and off through the gear ranges up to the final gear. Additionally, auto manufacturers never fully lock up the converter to hide engine performance idiosyncrasies with active fuel management systems with cylinder cancellation.
You will find an attached bulletin from General Motors (GM). This is one of many bulletins for this transmission. You will also find the scope data from this case study for the 2018 Chevrolet Colorado - You can see 90 RPM swings that are not intended. The first graph and the second graph are a simple move of the cursor to show the difference in RPM.
Other Related Articles
Chevrolet Suburban - 6L80 / 6L90E - Torque Converter Clutch Issues
List of Affected Vehicles Which Have the 8L45 or 8L90
2015-2019 Cadillac Escalade/Cadillac Escalade ESV
2016-2019 Cadillac ATS
2016-2019 Cadillac ATS-V
2016-2019 Cadillac CTS
2016-2019 Cadillac CTS-V
2016-2019 Cadillac CT6
2015-2019 Chevrolet Silverado
2017-2019 Chevrolet Colorado
2015-2019 Chevrolet Corvette
2016-2019 Chevrolet Camaro
2017-2019 GMC Canyon
2015-2019 GMC Sierra
2015-2019 GMC Yukon/Yukon XL
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General Motors 8-Speed Automatic Transmission Problems Case Study | GM Torque Converter Chatter Shake Shutter
2015 2016 2017 2018 2019 8L90 8L45
