Everything You Need To Know About GM Automatic Transmissions
If you’re looking for an indication of how much automotive technology has changed, one way is to count the number of forward gears in automatic transmissions. GM introduced the Powerglide back in the early 1950s and it employed only two forward gears. Shifting nearly 70 years into the 21st century and GM’s latest technology is now pushing 10 forward speeds with three overdrive ratios. We’ve come a long way, baby.
This story will outline the transformation, if you will, from the Powerglide all the way to the new 10L90E transmission that sits behind the 650 horsepower ZL1 supercharged Camaro with a dizzying collection of automatic gearboxes in between. We will briefly touch on the older transmissions like the TH350 and TH400 and the 700-R4 / 200-4R but since all of these gearboxes have earned a wealth of individual attention there’s little need to recap them here.
The focus of this story will be on the electronically controlled transmissions like the 4L60E, 4L80E,6L90E, 8L80E and the most current in the 10L90E. We’ll also clue you in on what those numbers and letters mean, although it’s far less complicated than trying to decipher Ford and Chrysler’s gearbox hieroglyphics. So let’s get started by first breaking down the alpha-numeric transmission identity puzzle.
The first number that appears is the number of forward gears followed by a letter that is only going to be either a T for transverse (front-wheel-drive or FWD) applications or L for longitudinal or rear wheel drive (RWD). The final two numbers relate to torque capacity with 80 and 90 offering much more load capability than a 30 or 40-rated transmission.
Before you fire up the email attacks, this story is intentionally ignoring a whole slew of GM automatics that are best described as obscure like the TH350C lockup, the TH475, the ill-fated TH-200, and several others. It's not that they didn't exist, only that their relevance is to collectors to collectors more than hot rodders. So let’s start with the simplest and oldest of the GM automatics.
It doesn’t get much simpler than a torque converter tied to a simple planetary First gear that then shifts directly into 1:1 for High gear. The ‘Glide was originally used in 1950 Chevy sedans using a cast iron case that later went on a weight reduction program courtesy of aluminum. The aluminum case appeared for 1962 and lasted until 1973, when it was supplanted by the three-speed TH350 in 1969. This was not GM’s first automatic. The first automatic was known as the four-speed Hydra-Matic (commonly referred to as the Hydro) introduced in 1940. This transmission used a fluid coupling as opposed to a torque converter and enjoyed limited use in early drag racing. The Hydro was quickly supplanted by the Powerglide. The GM two-speed was also fitted with two different First gear ratios, either 1.76:1 or 1.82:1, with the 1.76:1 ratio reserved for high-performance vehicles and some trucks, making the 1.82:1 version far more common.
Turbo-Hydramatic 350 (TH350)
The TH350 three-speed transmission replaced the Powerglide as the base automatic beginning in 1969. The TH350 employs a deeper 2.52:1 first gear ratio which improved initial acceleration compared to the Powerglide. Plus, with an interim second gear, this box was an immediate success for both street performance and drag racing. This trans can handle quite a bit of big-engine torque if built correctly yet has always played the little brother role to the real torque king – the TH400.
Turbo-Hydramatic 400 (TH400)
The top dog among the GM three-speed automatics appeared in 1965 in the passenger car lineup behind the 396 big-block, multiple truck applications, and later in the Camaro, Chevelle, and Corvette. The Turbo 400’s First gear ratio of 2.48:1 offered excellent gear multiplication and it soon became the first choice for street and drag racing applications based on its strength and durability. More than 50 years later, it retains much of its popularity and was the engineering basis for the four-speed overdrive 4L80E that appeared in the early 1990’s.
If the TH400 has a limitation, it is in its heavy rotating mass. Internally, it has to accelerate a very heavy direct drum that absorbs a measurable amount of power. The aftermarket has addressed this issue with a tremendous number of performance upgrades to the extent that a complete TH400 transmission can now be built with aftermarket parts – offering a tremendous number of different opportunities for street and race applications.
There are a couple of quick and easy ways to identify a TH400 compared to its smaller TH350 cousin. The TH400 places the vacuum modulator valve closer to the front of the case on the passenger side while the TH350 positions the valve at the very end of the main case on the passenger side. The TH400 is also significantly larger and heavier and uses a larger, 32-spline output shaft compared to the TH350’s 26-spline output that it shared with the Powerglide and Muncie four-speed manual gearboxes.
The first overdrive automatic to transfer power in the GM lineup was the 200-4R that arrived in 1981 behind A- and G-body cars as well as full-size sedans. This transmission is often mistakenly lumped in with the TH-200 three-speed automatic that GM attempted to make work in the early ‘80s. This is unfortunate since the 200-4R is in fact a very robust, true, three-speed automatic with a separate overdrive unit. This transmission eventually found favor when employed behind turbocharged Buick V6 cars like the Buick Grand National and GNX but could also be found in other applications like the G-body Monte Carlos SS and Oldsmobile 442.
The 200-4R was the first to replace the vacuum modulator valve with the throttle valve (TV) cable system. This system used a cable assembly tied to the throttle linkage as the load indicator to the transmission. As the cable moves, this increases line pressure in the transmission to properly apply and load the clutches and bands. In factory applications, this TV cable was properly adjusted and generally worked well.
Transmissions failures in aftermarket applications are often linked to improper installation and/or adjustment of this TV cable that results in low transmission line pressure that causes clutch slippage and transmission failure. But when properly built and modified, the 200-4R has outstanding potential as an overdrive automatic in a street performance application. Transmission builders such as Art Carr’s California Performance Transmissions and several others can assemble one of these transmissions into an excellent street trans.
Following the 200-4R one year later in 1982 was the 700-R4. While similar to the 200-4R, it operates somewhat differently, with a deeper First gear ratio of 3.06 vs the 200-4R’s 2.74:1 with a nearly similar 0.70:1 overdrive ratio. The 700-R4 also employs the TV cable arrangement to signal load to the transmission in exactly the same manner as the 200-4R.
There are actually two versions of the 700-R4, with the early ones employing a 27-spline input shaft that was upgraded around 1987 to a larger, more robust 30-spline input shaft that logically also requires a different torque converter. For nearly all performance applications, the later model 700-R4 is the transmission to use. The 700-R4 has suffered from a somewhat checkered reputation as a performance transmission in the aftermarket unfortunately due in large part to improper TV cable adjustment.
In 1990, GM changed its automatic transmission nomenclature and the 700-R4 became the 4L60. Despite the name change, operation of the transmission remained exactly the same. Despite the 700-R4 / 4L60’s somewhat undeserved reputation for problems, there is a wealth of aftermarket upgrade parts that make it capable of handling power well in excess of 500 to 600 hp.
GM upgraded the 4L60 to electronic control with the 1993 model year and these transmissions were used in a wide variety of applications from the Camaro and Corvette to full size cars and light and medium duty trucks. The big improvement was total electronic control which eliminates the need for the troublesome TV cable and also did away with the spinning weights and springs used in the governor, since input and output speeds are now measured by sensors and the up and down-shifts are controlled by an electronic transmission controller.
The advantage for the performance enthusiast is that this transmission can now be controlled electronically to up-shift at wide-open-throttle at very specific engine speeds which was difficult to achieve with the 700-R4’s mechanical/hydraulic control. Plus, the torque converter lockup could also now be controlled with the same ECU. There are multiple companies now that offer a stand-alone controller for the 4L60E family of transmissions, including the MSD Atomic Transmission Control Module, and both Holley’s Dominator and Terminator X ECU versions also offer transmission control over the 4L60E/4L80E family of four-speed automatics.
The 4L60E went through some case changes during its tenure. The ’93-’97 versions used a one-piece or integrated bellhousing much like earlier TH350 andTH400 transmissions. In 1999, the 4L60E converted to a bolt-on bellhousing. One year later, in 2000 it changed again with a deeper bellhousing to accommodate a 300mm input shaft and larger torque converter. This last one can be identified by its bellhousing bolt hole located at the 12 o’clock position.
There are also several performance variants to the original 4L60E including those from, B&M. The big durability factor is aftermarket and heavy-duty factory pieces that push the original 4L60 trans well into 4L80E torque territory.
Looking to improve highway mileage on late model trucks, beginning in 1991 GM upgraded the original TH400 by adding a 0.70:1 overdrive along with complete electronic control to create the 4L80E. This trans is significantly larger and heavier than its three-speed predecessor, but like the 4L60E it is easily employed for performance use in earlier vehicles by using the same aftermarket controller that manages the 4L60E.
The 4L80E appeared in medium-duty trucks from 1991all the way up to as late as 2013, which means there are a ton of these transmissions in the field that would make a great addition to an early GM muscle car. This trans will fit under most ‘60s floor pans with a few modifications.
There is an early and late variation on the 4L80E. Internally, both versions are essentially the same in terms of torque capacity. Early versions position both the inlet and outlet cooler lines up near the bellhousing while the later variant that appeared in 1997 moved the return side cooler line to the rear of the transmission to assist in lubrication.
Several other aftermarket transmission companies offer stages of performance builds that will increase this transmission’s already-stout torque capacity with multiple internal upgrades.
The next rung in the transmission ladder bumps up to six forward gears with the 6L80E with two overdrive ratios. This transmission is considered the beginning of what was a major engineering advancement where each gear change was accomplished using what is called clutch-to-clutch gear changes instead of using bands and over-running clutches with previous automatics. Among the more interesting features is that this transmission placed the computer inside the oil pan.
Perhaps of more importance is that this transmission also dramatically deepened the First gear ratio from the TH400/4L80E’s 2.48:1 to a radical 4.02:1. Digging even further, this transmission goes against the grain with a 1.15:1 fourth gear instead of the more traditional 1.00:1. On the overdrive side, it employs two ratios spinning 15 and 33 percent faster than the input.
A variant of the 6L80E was first used in the 2006 -’14 Corvettes as well as several truck models including a 6L90E version in a 2500HD series Silverado truck. It also appeared in the ’09-’13 Cadillac CTS-V in a 6L90 configuration. The Corvette usage means that this trans was behind both the Gen IV 6.2L LS3 as well as the direct-injection LT1 Gen V engines. If you look closely at the photos of the 6L80E, you can see both the traditional 12 o’ clock bellhousing bolt hole position as well as a drilled hole shifted to the passenger side to accommodate the position of the Gen V’s mechanical fuel pump.
The Chevrolet Performance 6L80E trans comes with a set of wiring harness adapters and a flash drive that is used to configure the transmission to be used behind a GM LS engine in a rear wheel drive application. Swapping to this transmission is currently difficult from an electronic control standpoint.
Once GM made the move to the six-speed, it didn’t take long to upgrade from six to eight forward speeds with the introduction of the 8L80E with the 2015 Corvette and Silverado pickups and GMC Denali and the Camaro in 2016. The eight-speed transitions the gear ratio chart is even deeper by using a 4.56:1 First gear and adding another ratio in between First and its 1:1 sixth gear while maintaining two overdrive ratios.
If we combed this deep 4.56:1First gear ratio with a theoretical 2.48:1 rear axle ratio, this combination would be exactly the same as an early muscle car with a TH400 (2.48:1 First gear) with a 4.56:1 rear axle gear. The obvious advantage for the 8L80E is that once it hits Sixth gear at 1:1 it still has two overdrive ratios to employ for excellent highway cruising. That hypothetical, old-school Camaro would still be stuck with a 4.56:1 rear axle ratio and no overdrive.
The 8L80E and its performance variant the 8L90E were built to be used behind the Gen V V8 applications with a bellhousing bolt pattern specific to the Gen V engines. This means that it cannot be used with previous Gen III/IV LS engines because with the missing top bellhousing bolt, the span between the top of the transmission is too wide and can cause stress fractures to the case.
Perhaps more importantly, this transmission has adaptive learning capability built into the software and also has moved the control module outside the transmission. While Chevrolet Performance offers the 8L90E, it is only offered for use with choices of an LT1, or supercharged LT4/LT5 engines with specific matched ECUs.
GM and Ford created a joint venture program in which GM was to design and build a nine-speed transaxle while Ford would create a heavy-duty 10-speed automatic for use in rear wheel drive applications. The GM version of this new 10L80E / 10L90E employs a 4.70:1 First gear ratio. The transmission initially appeared in multiple 2017 vehicles such as the Cadillac Escalade, GMC Suburban, and eventually in the Camaro SS ZL1 package.
The transmission uses an externally mounted transmission control unit along with a 260mm (10.2-inch) diameter torque converter. Torque capacity for the stock Tahoe application is rated at 460 lb-ft, while Chevrolet Performance rates its 10L90E version at a much more aggressive 715 lb-ft of torque. The transmission weighs around 230 pounds and is only available through Chevrolet Performance for use behind the Gen V engines such as the LT1, LT4, and LT5. This is mainly due to the fact that the 10L80E / 10L90E transmission case features a bellhousing pattern that is only applicable to the Gen V engines with their relocated top bellhousing bolt location.
This new generation of clutch-to-clutch transmission requires very sophisticated control mechanism and much of the performance capabilities are tied into input and output shaft speeds. The ECU also has a self-learning function along with a sport mode that creates higher line pressures for firmer shifts and higher rpm shift points. Along with its other unique features, this new gearbox does not offer an external dipstick and requires the use of GM’s new Dexron HP ATF fluid.
Alphanumeric Designation - Late Model Transmissions
|First Number||Forward Gears (4-10)|
|Second Letter||L = Longitudinal (RWD), T = Transverse (FWD)|
|Third and Fourth Number||Torque Rating (larger number, stronger torque rating)|
|Fifth Letter||E = electronic control|
While two and three-speed automatics dominated the automotive world for decades, in the last 20 years, we’ve seen a major surge in ratios that currently top out at 10 forward speeds that include three overdrive ratios. All of this does improve performance and durability, but it also comes at the price of size, weight, and complexity that will no doubt add to rebuild costs. We’ve come a long way from the old Powerglide.
|700R-4 / 4L60E||3.06||1.63||1.00||0.70|
|6L80E / 6L90E||4.03||2.36||1.53||1.15||0.85||0.67|
- - Powerglide was also offered with 1.82:1 First gear.
|Transmission||Output Spline Count and Style|
|10L90*||28 Male with keyway|
- - Most truck applications use a slip-on yoke while cars use a bolt-on yoke.
Torque Capacity Listings For Late Model GM Overdrive Automatics
- * These torque ratings are for the aftermarket Chevrolet Performance transmissions. The remaining listings are stock transmission ratings that tend to be more conservative. Note for instance the significant difference in torque capacity between the Chevrolet Performance 4L85 and the production 4L80E. It is likely that the stock 4L80E can handle much more torque than the factory rating of 440 lb-ft.
Automatic Transmission Fluid Requirements
|Powerglide, TH350, TH400|
200-R4, 700-R4, 4L60, 4L60E
|Dexron III (H)|
|4L60E, 4L70E, 4L75E, 4L80E,|
|8L80E, 10L80E, 10L90E||Dexron HP|
If you study this chart, it’s obvious that things have changed in the world of ATF. It used to be there were two fluids – GM’s Dexron and Ford Type F. But that is no longer true. Even Dexron VI is not even applicable across the board. Late model transmissions demand that the correct fluid be used – as with the 10L90E transmission using Dexron HP.
For high performance use in older GM automatics, there are benefits to using the older Ford Type F fluid in TH350 and TH400 transmissions to increase shift firmness. Type F does not add friction modifiers to the fluid. Do not use Type F in any transmission requiring Dexron VI or Dexron HP fluid. The Dexron HP is defined as an ultra-low viscosity (ULV) fluid. An example of the GM HP fluid would be Mobil 1 LV ATF.
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