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2019 Cadillac CT6 PremLux replacing 2017 CT6#2, Replacing CT6#1
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GM’s 8L45 Eight-Speed Cadillac CT6 Automatic Transmission: Recall, Replace, Re-tune or Deny

GM’s 8L45 Eight-Speed Automatic Transmission, currently churning away in Cadillac's CT6, is a clunker. GM’s customer assistance center acknowledges that the reviews are ‘mixed’ and one service bulletin has been issued. The ‘mixed’ aspect of the feedback shows that this 8L45 works normally for a while for some owners. Internet forums are heating up with discussions about otherwise fine cars cursed with this crude, confused and embarrassingly bad 8 speed lemon.

General Motors has managed to take its customers back several decades to an unpleasant time in the early development of the automatic transmission. The GM 8L45 Hydramatic Transmission is part of the powertrain in the Cadillac CT6, CTS, ATS, Chevrolet Camaro and perhaps more vehicles under a different name. This questionable feat of backwards design and engineering was accomplished with variable force solenoid technology, speed sensors and a processor executing hundreds of calculations and commands every 6.25 milliseconds. Clearly, this is not often enough, as evidenced by the ride experience inflicted on the driver and passengers when the thing desperately hunts for the proper gear and any gear will do … to lurch forward. With all that technology it performs far worse than the bands and torque converters of that our grandparents enjoyed in the 1960’s and later. In 2016, General Motors was simply not ready to evolve past the 6 speed transmission but that didn’t stop it from going ahead and cursing entire fleets of its new vehicles with the crudest powertrain component in its history. And yes indeed, it weighs over 30 lbs. less than its predecessor (one that actually works, though evidently grossly overweight). Perhaps the elusive 2nd, 3rd and 4th gears each weigh 10 lbs., accounting for both the weight loss and crude performance.

The 8L45 is a mess. Its crude state of performance sometimes rears its ugly head on a new GM vehicle on its way home from the dealership, or lurks deep inside its innards for a later outbreak of hard shifts, flares, thunks, and head jerking downshifts at random times in the early lives of the fleet. GM’s confidence with this clunker drove it to install it in the Cadillac CT6, CTS and ATS models. Dealerships are forced to appease customers with such phrases as ‘performs as designed’ and ‘performed adaptive fast learn’ as a way to force owners to get used to it. The other line of defense is that the transmission is learning and adapting to the driver’s style. Enduring the explanations and excuses of GM service technicians and service managers can be tiring. Confidentially, they’ll admit that the thing is a disaster.

Other than a single service bulletin, GM is ignoring this failure as of Spring 2017. To admit there’s a problem would be a devastating blow to the marketability of its current unsold inventory. There is also a lot of ego at stake here. GM promoted the 8L45 in its literature in a series of puffed up articles with statements like this:

“The 8L45 was designed to enhance the CT6’s driving experience, offering a strong balance between performance and efficiency,” said Bill Goodrich, GM’s assistant chief engineer for eight-speed automatic transmissions “Perhaps its best attribute will be that customers really won’t notice it – they’ll simply enjoy the CT6’s seamless, smooth driving experience and on-demand performance.”

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The owner of a vehicle cursed with this clunker will know there’s a problem when passengers ask why the brakes are being pumped when coasting to a stop. That’s the 8L45’s attempt at downshifting. When the driver gingerly feathers the accelerator to coax the thing into gear after an auto-stop shutdown it may skip several gears and slam into 4th or 5th with a violent shutter. The driver and passengers all feel it as the entire vehicle shutters. At times it may seem like the driveshaft is going to come up through the cupholder and cellphone battery charger. Its performance is indefensible. If it’s shifting like an average GM vehicle and it hasn’t yet slipped into this confused state, it soon will. No amount of learning, adaptive fast learns or software tunes can apparently help it find the right gears, other than reverse or park, which, luckily seem to work. Dealer lots are filling up with unsold inventory and returned vehicles, many with less than 2000 troubled miles on the odometer. Apparently, frustrated owners were not able to adapt and learn along with the car’s stuttering, clunking, and confused transmission.

So, what is the future of the 8L45? Maybe a software tune can bring it under control. If this is not possible, and clearly, GM is in no hurry to resolve this issue, the fate of the 8L45 has these possible futures:

1. It will quietly disappear in 2018, leaving the current fleet in an abyss of wildly unpopular clunkers. The CT6 is becoming known as the shimmying, stuttering, lurching flagship that looks nice.

2. It can finally break in at 40,000 miles or so and can then find the correct gears at appropriate times after a few years of learning and adapting.

3. Third party after-market companies will offer a way to replace and retrofit it with a nicely functioning transmission, like the 6L45, thus salvaging the resale value of the CT6 and others.

Corporate denial doesn’t help the brand. Blaming the customer for expecting better shifting insults the brand loyalists. It’s clear that the 8L45 was rushed into production without quality engineering and design. Hopefully, GM and its Cadillac division can conjure up a solution that can make its attractive CT6 flagship drive as nicely as it looks parked.
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