The Biggest Problems With Gm's 8-speed Transmission

For years, automakers were reliant connected 6-speed transmissions. However, they began to adopt 8-speed replacements, pursuing unit from nan authorities to meet caller biology regulations. When nan 8-speed gearbox kicked disconnected successful nan mid 2000s, it was recovered to devour little substance per mile and produce fewer c dioxide emissions. General Motors decided to subordinate nan statement rather precocious successful 2014, erstwhile it released its heavy-duty 8L90 to switch its 6-speed 6L80, respective years aft different manufacturers had implemented their ain 8-speed transmissions.

The 8L90 went into much demanding models for illustration nan Silverado and Corvette. A spot later, nan 8L45 was introduced for little rigorous applications and recovered a location nether nan hood of vehicles for illustration nan Cadillac and Colorado.

Unfortunately, nan move to nan 8L transmissions didn't spell arsenic smoothly arsenic nan automaker had hoped, arsenic location were immoderate important issues pinch these 8-speeds. With reports of shaking, difficult shifts, and hesitation, galore are leery of GM's 8L bid transmissions. 

One of nan hallmarks of a bully transmission is really soft nan cogwheel shifts consciousness down nan instrumentality arsenic nan conveyance accelerates. How your automatic transmission knows erstwhile to alteration gears is apt acold much analyzable than you whitethorn imagine, truthful diagnosing issues wrong it tin beryllium arsenic challenging. Unfortunately, for galore GM drivers pinch an 8-speed transmission nether nan hood, nan knowledgeable was rather nan other of smooth. Several reports picture pronounced vibrations during normal driving. Obviously, this behaviour severely dampens thrust quality, and it apparently affects thing from Camaros to Yukons and different GM vehicles.

So, what could beryllium responsible for this stuttering that plagues immoderate GM drivers pinch 8L bid transmissions? Well, early successful 2020, a method work bulletin (TSB 18-NA-355) was released to shed immoderate ray connected nan problem that affects various GM models from 2015 done 2019. A much precise explanation of nan rumor was included, adding that nan behaviour occurs betwixt 25 and 80 mph during ray acceleration. The bulletin claims that nan torque converter clutch (TCC) is nan root of nan vibration and recommends replacing nan aged transmission fluid pinch a caller type.

Another communal title among GM drivers pinch 8L90 and 8L45 transmissions is that nan gearbox lurches when going into 2nd gear. Some drivers person described nan problem arsenic if they were successful mobility and revved nan motor successful neutral and past abruptly threw it into gear. Others picture nan rumor arsenic being much severe, characterizing it arsenic nan emotion of different motorist crashing into nan rear of nan vehicle.

Fortunately, nan recommended hole described supra besides seems to correct nan unsmooth displacement into 2nd cogwheel problem. The caller recommended fluid is bluish explanation Mobil 1 synthetic HP, and immoderate outlets declare that pursuing a transmission fluid flush, things look to person improved for immoderate drivers. However, for those still dealing pinch these issues, it surely puts a damper connected nan GM acquisition — not dissimilar different examples of great cars that were ruined by their transmissions. One poster connected Car Complaints noted that their Sierra 1500 Denali still lurches during shifting, contempt pursuing nan guidance outlined successful nan work bulletin. The poster goes connected to opportunity that GM dealers person been small thief and that immoderate of them couldn't moreover replicate nan issue.

So, not only person GM's 8L45 and 8L90 transmissions exhibited shaking during acceleration and difficult shifts into 2nd gear, but owner's person besides reported delayed shifts betwixt gears. Essentially, it's almost for illustration nan transmission isn't rather judge which cogwheel to gaffe into. 

Some hypothesize that these issues pinch GM's 8-speed gearbox are related to nan computer, making this a package problem, not a mechanical one. A 2015 method work bulletin outlined nan steps required to reprogram nan transmission power module (TCM) successful prime GM vehicles pinch nan 8L90 (M5U) transmission. In fairness to GM, programming errors successful nan TCM person been progressive successful respective of the worst transmission recalls of nan past 5 years, affecting aggregate automakers. 

The shaper did present a caller transmission version successful 2019, nan MQE, which replaced nan M5U. GM promised that nan caller version would bring pinch it improvements. Nevertheless, immoderate drivers are still reporting problems and cautioning against purchasing an 8-speed from GM, particularly considering that nan automaker is embroiled successful aggregate people action lawsuits related to its transmissions.