Numerous class-action suits have been filed against GM over its 8L45E and 8L90 eight-speed automatic transmission. Plaintiffs claim the eight-speed automatic transmission will slip gears, shift. TSB Seems To Fix 8-Speed Automatic GM Transmission ProblemsAugust 13, 2019 Multiple GMC Acadia Owners Report ‘Shift To Park’ Issue December 13, 2019 Poll: Should GM Bring Back Pontiac? EPA-estimated MPG city/highway: Camaro LS/LT with 2.0L 4-cylinder engine and 8-speed paddle-shift automatic transmission 22/30; Camaro LS/LT with 2.0L 4-cylinder engine and 6-speed manual transmission 19/29.

The GM 8-speed 8L45 Hydramatic Automatic Transmission from GM Powertrain OEM Sales makes the most of its horsepower and torque to optimize performance. The all-new Allison 10-speed 10L1000 automatic transmission (RPO MGM, MGU) available on 2020 Silverado HD and Sierra HD models equipped with the 6.6L Duramax diesel engine combines enhanced performance, fuel economy, and operational flexibility with an industry-leading reputation for reliability.

The all-new Allison 10-speed 10L1000 automatic transmission (RPO MGM, MGU) available on 2020 Silverado HD and Sierra HD models equipped with the 6.6L Duramax diesel engine combines enhanced performance, fuel economy, and operational flexibility with an industry-leading reputation for reliability. Designed for high-performance and low-maintenance, the new 10-speed transmission (Fig. 14) — the first-ever offered in the heavy-duty pickup segment — has been tested and validated in partnership with Allison Transmission and, combined with the proven Duramax 6.6L diesel engine, offers a powertrain combination that provides superior power delivery and productivity.

The Duramax/Allison powertrain standard axle ratio has been reduced to 3.42:1, which lowers engine speed, enhances refinement and increases efficiency. The powertrain combination is available on 2WD or 4WD models.

Fig. 14

Transmission Architecture

The transmission has 10 speed ratios that are generated using four simple planetary gear sets, two brake clutches, and four rotating clutches. The on-axis transmission architecture uses a squashed torque converter, an off-axis pump and four close-coupled gear sets. The four rotating clutches are located forward of the gear sets to minimize the length of oil feeds that provide for enhanced shift response. There are different variants of the transmission, all based on torque capacity. Architecture is common between the variants, and component differences are primarily related to size.

The transmission architecture features a case with an integral bell housing for enhanced powertrain stiffness. (Fig. 15) A unique pump drive design allows for off-axis packaging very low in the transmission. The pump is a variable vane type, which effectively allows for two pumps in the packaging size of one. This design and packaging strategy provides for ideal oil routing to the controls system with the pump located in the valve body itself.

Fig. 15

The 4-element torque converter contains a pump, a turbine, a pressure plate splined to the turbine, and a stator assembly. (Fig. 16) The torque converter acts as a fluid coupling to smoothly transmit power from the engine to the transmission. It also hydraulically provides additional torque multiplication when required. The pressure plate, when applied, provides a mechanical direct drive coupling of the engine to the transmission.

Fig. 16

The hydraulic system primarily consists of an off-axis gear-driven variable vane-type pump next to the valve body, and two control valve body assemblies. The pump maintains the working pressures needed to stroke the clutch pistons that apply or release the friction components, which consist of six multiple disc clutches. The multiple disc clutches deliver 11 different gear ratios, 10 forward and one reverse, through the gear sets.

Transmission Control Solenoid Valves

The Transmission Control Module (TCM), which is externally mounted, uses three speed sensor signals for enhanced shift response and accuracy .The TCM receives and monitors various electronic sensor inputs and uses this information to shift the transmission at the optimum time.

The 10-speed transmission could contain a maximum of nine individual solenoids — RPO dependent — installed in various bore locations on the lower control valve body assembly and internal transmission case. Eight of the nine solenoid valves are used to control pressure regulation and direction of transmission fluid. The one on/off solenoid valve is only used to direct transmission fluid. The normal operating current range for these solenoid valves is between 0–1.2 amps. If the TCM detects an electrical circuit malfunction or excessive current flow, the TCM will turn off the high-side driver to that solenoid and set a DTC.

Transmission control solenoid valves 1–8 are pressure regulating valves. Each solenoid valve is tested after assembly to determine the output fluid pressure at certain electrical values, applied to the coil winding, and is referred to as solenoid current/pressure data points. The current versus pressure data points are saved and assigned a file number, which is marked on the solenoid valve housing end or on the valve body itself. The solenoid performance data file is programmed and stored in the vehicle’s TCM as well as stored on the Techline Information System (TIS) website. Replacing any of the following components require the TCM to be programmed with either the new or existing solenoid valve performance data, depending on what component is replaced.

• Transmission assembly – program the TCM with the new data file stored on the TIS web site for all pressure regulating solenoid valves.
• Lower control valve body assembly with solenoid valves – program the TCM with the new data file stored on the TIS web site for all pressure regulating solenoid valves.
• Transmission Control Module – program the TCM with the existing data file stored on the TIS web site for all pressure regulating solenoid valves.
• One or more solenoids – program the TCM with the new data file stored on the TIS web site for all pressure regulating solenoid valves that were replaced.

Power Take-Off

The available all-new factory-integrated, engine-driven Power Take-Off (PTO) eliminates the need for an aftermarket unit. Exclusively offered with the 10-speed transmission (RPO MGU) on select diesel models, it’s the first fully integrated PTO system in the HD truck segment, with the PTO’s drive gear operated via chain to direct engine power. (Fig. 17) And because it is engine-driven rather than turbine-driven, the PTO can be used while the vehicle is idling. A button inside the cab enables the PTO, and a mode selector allows adjustment of load and torque output.

Fig. 17

Gm 8 Speed Transmission Fluid Check

– Thanks to Kevin Minor and Sherman Dixon

— A General Motors 8-speed transmission lawsuit alleges fixes offered by the automaker haven't solved problems with hard shifting, shaking, jerking, hesitating and shuddering.

The proposed class-action lawsuit includes all consumers who purchased or leased the following vehicles in California, Florida, Illinois, New York, Oklahoma and Texas:

• 2015-2019 Chevrolet Silverado
• 2017-2019 Chevrolet Colorado
• 2015-2019 Chevrolet Corvette
• 2016-2019 Chevrolet Camaro
• 2015-2019 Cadillac Escalade
• 2015-2019 Cadillac Escalade ESV
• 2016-2019 Cadillac ATS
• 2016-2019 Cadillac ATS-V
• 2016-2019 Cadillac CTS
• 2016-2019 Cadillac CT6
• 2016-2019 Cadillac CTS-V
• 2015-2019 GMC Sierra
• 2015-2019 GMC Yukon
• 2015-2019 GMC Yukon XL
• 2015-2019 GMC Yukon Denali XL
• 2017-2019 GMC Canyon

The GM vehicles are equipped with GM 8L45 or 8L90 automatic transmissions that allegedly hesitate when drivers accelerate or decelerate. Drivers claim the transmissions can shift so hard it feels like being hit by another vehicle. One owner claims the GM transmission shifted from REVERSE to DRIVE so harshly the vehicle almost went through the garage door.

Every 'fix' offered by the automaker has allegedly failed to repair the shaking, shuddering and jerking, and the plaintiffs claim both the torque converters and transmissions cause problems with the hydraulic systems and gears.

Court documents claim metal shavings allegedly circulate throughout the transmissions and damage the components. Additionally, the plaintiffs claim the 8-speed transmissions cause consumers to face expensive repairs to flush the systems, and to replace the valve bodies, torque converters and finally the transmissions.

According to the proposed class-action lawsuit, General Motors has allegedly known about the 8-speed transmission problems because the automaker has issued multiple versions of technical service bulletins (TSBs) about the transmissions.

GM dealers have been told to perform certain repairs to fix the transmission issues, including performing the “clutch drive learn procedure, replace the valve body, replace the entire transmission, flush the cooler lines and cooler, remove debris from and clean the transmission pan, replace the transmission filter, replace the transmission fluid, and flush the transmission.'

The lawsuit alleges no fix works and GM is fully aware of it, something allegedly reflected on repair orders. The plaintiffs say repair notes indicate, “GM is aware of concern and a release date of late January/February to correct issue.” Another repair order allegedly said, “no repair available until quarter 1 in 2019.”

According to the lawsuit, General Motors is doing nothing but stalling, buying time until vehicle warranties expire. The automaker also allegedly conceals from consumers the serious problems with the 8-speed transmissions even though dealers have been told.

GM issued a preliminary information bulletin (PIP5337) to dealerships about 8L90 transmissions entitled, “Shake or Shudder on Acceleration Excessive Engine RPM Fluctuation.”

The bulletin covered 2015-2016 Cadillac Escalades and Escalade ESVs, 2015-2016 Chevrolet Silverados and 2015-2016 GMC Sierras, Yukons and Yukon XLs. GM told technicians that customers may report, “A shudder feeling that may be described as driving over rumble strips or rough pavement.”

“These conditions may be caused by an internal torque converter issue. A revised torque converter that addresses these conditions will be available soon.”

In June 2016, GM issued TSB 16-NA-014, entitled “Delayed Engagement After Sitting With Engine Off' about 8L45 and 8L90 transmission. Technicians were told customers may complain about multiple issues: “Vehicle delaying into gear,” “Not wanting to move,” “Feeling like the transmission is slipping,” or “Delayed engagement followed by a harsh engagement.”

“This condition may be caused by the torque converter draining the transmission fluid back into the transmission pan.”

Technicians were told to replace parts of the transmission or pan.

The plaintiffs claim the automaker knew the 8-speed transmissions were wearing out early and causing metal shavings to build up in the transmission pans. This is allegedly reflected in TSB 16-NA-175 entitled, “Shake and/or Shudder During Light Throttle Acceleration, Between 48 and 104 KM/H (30 and 65 MPH) at a Steady State.”

GM technicians were told vehicles equipped with 8L90 transmissions could experience “A shudder feeling that may be described as driving over rumble strips or rough pavement.” Technicians were advised to flush the transmission with new fluid and “clean the pan/magnet if any metallic particles present and replace filter if debris is found.”

Another bulletin was issued in December 2017 allegedly claiming transmission shudders affected all 2015-2018 “GM passenger cars and trucks” equipped with 8L45 or 8L90 transmissions.

Gm 8 Speed Transmission In Trucks

According to the lawsuit, GM technicians have also been told:

“Do NOT replace the torque converter or transmission assembly for this condition. Engineer reviews have proven that replacing the torque converter does not provide a long-term solution to TCC [torque converter clutch] shudder. A revised service procedure will be released in Q1 of 2019. If the vehicle experiences a repeat shudder condition, this document should be followed again.”

The plaintiffs also claim the automaker says the automatic transmissions are “adaptive” and need to “learn” the individual driving habits in order to shift smoothly.

The General Motors 8-speed transmission lawsuit was filed in the U.S. District Court for the Southern District of Florida - Duffy, et al., v. General Motors, Inc.

Gm 8 Speed Transmission Lawsuit

The plaintiffs are represented by Cohen Milstein, and Gordon & Partners.

Gm 8 Speed Transmission Fluid Check

CarComplaints.com has owner-reported complaints about the GM vehicles named in the proposed transmission class-action lawsuit.