It wasn’t that long ago when an automatic transmission having four gears was considered high tech. Automatic transmission design has continued to advance, and now, these hydraulic marvels possess six, eight, and even ten forward gears. While this is great for fuel mileage and driving long distances, we want to know if one of these new gear changers can handle any sort of performance.
We decided to take a look at GM’s 8L90-E eight-speed transmission that is becoming a favorite with performance enthusiasts. While these are solid transmissions to hang behind a built LS or LT engine, there is always room for improvement. To find out more about that, we reached out to ATI Performance Products, Inc. to get an understanding of where this heavy-duty transmission could be improved upon and how to make those improvements. But first, a little history for our vintage Chevy muscle car fans to catch them up with the electronically-controlled slushbox.
When the ’90s rolled around and cars were adding more and more electronics under the hood, new technology, like drive-by-wire, became a reality. Almost unnoticed at the time, GM’s Hydramatic transmissions had begun the move to electronic versions.
The early electronic transmissions were based on the tried-and-true Turbo-Hydramatic design. Those transmissions infused with modern electronics used the “-E” designator to identify them as different from the mechanical versions.
A Quick Rundown Of GM’s Electronic Transmissions
Here’s a brief look at the family tree of the electronic transmissions used by GM since 1991. The first generation of electronic transmissions designed for use in rear-wheel-drive vehicles – referred to as “longitudinal” transmissions – hit the streets in four-speed architecture across various applications. In 1991, the 4L30-E transmission was used in light-duty passenger cars. Heavy-duty trucks had the 4L60-E and 4L65-E available in 1991. In medium-duty trucks and passenger cars, both the 4L60-E and 4L65 were deployed in 1992.
The next generation of longitudinal transmissions used in GM cars is a little more eclectic, with several ratios and number of gears ranging from five to eight-speeds for commercial use. The 10L90-E looks to be the new standard after its 2017 introduction. There is even a ten-speed available for GM performance cars. Here’s the second-gen breakdown:
- 5L40-E and 5L50 (2000-2007). A five-speed medium-duty transmission.
- 6L45 and 6L50 (2006-present). A six-speed medium-duty transmission.
- 6L80 and 6L90 (2006-present). A six-speed heavy-duty transmission.
- 8L90 (2014-present). An eight-speed heavy-duty transmission.
- 8L45 (2016-present). An eight-speed light-duty transmission.
- 10L80 (2017-present) A Ford-GM ten-speed in light trucks/SUVs.
- 10L90 (2017-present) A Ford-GM ten-speed in performance cars.
- 10L100 (2017-present) Allison-GM ten-speed in medium-duty trucks.
The Ford-GM transmissions are a joint venture between GM and Ford that splits the development of two-transmissions between the automotive giants. Ford led the design of the ten-speed transmission and GM was responsible for designing the nine-speed, transverse automatic gearbox used in many front-engine SUVs. GM is allowed to use the ten-speed transmission with rights to modify and manufacture it for its own applications, with Ford having the same rights to the nine-speed. In the end, Ford declined the use of the 9T.
A Deep Dive Into The 8L90-E
The 8L90-E is an eight-speed automatic transmission with gear ratios of 4.56, 2.97, 2.08, 1.69, 1.27, 1.00, 0.85, 0.65, and a Reverse gear ratio of 3.82. It is manufactured with a standard bell housing unit for front-engine/rear-wheel-drive cars. The unit was designed for use with the GEN-V LT1, LT4, or LT5 engines.
With a numerically higher (4.56:1) first gear ratio for stronger take-off performance, the transmission also employs a double-overdrive sixth-gear ratio of 0.65:1 to help optimize cruising efficiency. The 8L90-E is equipped with a slip-yoke tail shaft for use with the LT1 engine and a fixed-yoke design for use with the LT4 and LT5 engine platforms.
Many vehicle owners with the stock 8L90-E have reported an inherent “shudder” issue and harsh shifting problems with the transmission. GM issued a Technical Service Bulletin TSB 18-NA-355, with updates that address the “torque converter clutch (TCC) shudder conditions.”
The problem was identified by many customers who reported the transmission shuddering frequently and shifting harshly between first and second gear. The same harsh shifting was identified when shifting down between second and first gear. The issue was magnified when accelerating during the upshift or decelerating in the downshift.
GM identified a fluid flush as a probable fix for the issue. This is plausible, given the explanation by the automaker. According to GM, the issue was caused by “moisture content in the transmission fluid.” The old GM transmission fluid was to be swapped out for Mobil 1’s new synthetic LV ATR HP fluid, which seems to have solved many of the issues.
Upgrades With ATI Performance Products
Even with the “shudder” issue solved, the stock eight-speed GM transmission can be improved with performance upgrades from ATI for serious driving enthusiasts. These upgrades include increased clutches and different clutch materials for performance applications. “ATI starts with an LT4 clutch drum that holds an extra clutch,” explains ATI’s Chief of Operations, JC Beattie Jr. “The supercharged cars came with this drum from the factory.”
Anyone interested in having an ATI-rebuilt 8L90-E transmission can have their unit rebuilt, along with the stock converter, or receive a new, multi-friction lock-up, billet converter. But, enthusiasts who have knowledge of automatic transmissions can purchase the upgrade components to “soup-up” their own transmission. The master overhaul kit (part number 706520) for an 8L90-E includes Raybestos’ upgraded friction components – manufactured with GPZ high-energy fibers for durability – and all paper, clutches, seals, and rings needed to overhaul the unit.
Making Lots Of Power Or Towing Some Series Weight?
Added available goodies include a Vasco input shaft (part number 704000) that is made from heavy-duty Vasco Max Aerospace steel. It is designed to be strong and resilient enough to handle even the most severe torsional shock. It works like a torsional spring bar that is designed to twist and then return to its original form. Not only does this configuration eliminate breakage, but it also reduces shock to the gear train. According to company literature, “The shaft is made from 100-percent American-made heat-treated steel from raw bar stock to hobbing millwork, heat-treated, and then finish ground in-house,” said Beattie Jr.
If you are lucky enough to be behind the wheel of a C7 or ZR1 Corvette equipped with the 8L90-E, ATI’s 300M output shaft (part number 704050) may be a wise upgrade. This heavy-duty shaft is a direct replacement for the OEM unit and requires no modifications.
“The units we were getting in from the high-horsepower Corvettes started to show a lot of wear on the teeth, so an upgrade was needed,” explained Beattie Jr. “The output shaft can be installed when the transmission is in the car, but it is certainly not the best way to do it, and by the time you are there, you only have a few other things to unbolt to get the transmission out. If you are twisting your stock output shaft or hurting the teeth and need to install this part, you most likely need the upgraded clutches and input shaft as well,” he added.
If you are wondering how much power this shaft can hold, it’s a lot. “Harvey Baker, a sales associate at ATI Performance Products, says, “This output shaft uses the same material as our 3,500 horsepower Turbo 400 output. We don’t have a horsepower rating yet, but it will outlast the rest of the components in the transmission.”
For those wanting maximum performance in higher horsepower applications, a separate HDXTREME clutch and friction kit for the eight-speed transmission is currently being tested by ATI and is expected to hit the market soon. This kit is designed to increase holding capacity by 21- to 40-percent in all positions. It will feature American-made billet-steel pressure plates with high-performance frictions and new steels. As of this writing, this kit is in the vehicle-testing phase.
It’s a simple proposition to get the transmission upgraded with parts from ATI and even combine it with an ATI torque converter designed for any application. If you’re building a restomod and are considering a late-model drivetrain, this combo would be a great choice for everything from a street rod to a ’69 Camaro Pro-Touring car, to a weekend drag car. When it’s mated to an LT1, LT4, or LT5 crate engine, the GM Connect and Cruise package makes it an easy install.
For more information on ATI’s upgraded transmissions or any of the performance products mentioned here, visit them online at www.atiracing.com.