Mustang Automatic Transmissions | Essential Guide

Automatic transmissions are the most common kind of transmission found in vehicles built in the U.S. today. Although, their history in Mustangs goes all the way back to the beginning. Earlier Mustangs would come equipped either with a 4-speed manual or a 3-speed automatic.

With Foxbodies, the coveted 3-speed C4 and C5 Ford transmissions would still live on, though the addition of an automatic overdrive, or AOD, 4-speed transmission was brought on board. This made for a total of three different transmission options available to the Foxbody platform.

A unique characteristic of the Mustangs is they're regularly paired with Tremec manual transmissions with more and more options available to each subsequent generation. When it comes to automatic transmissions, however, only one per generation has been available since the last Foxbody rolled off the assembly line. The SN95 was paired with a 4-speed automatic, the S197 a 5-speed, and the S550 with a 10-speed, all being overdrive units.

Foxbody (1979-1993) Auto Transmissions:

• C4 3-Speed (1979 5.0L, 1980-1982 4.2L)
• C5 3-Speed (1980-1982 4.2L)
• AOD 4-Speed W/Overdrive (1984-1993 5.0L)

SN95 (1994-1998) Auto Transmissions

• A0D-E (1994-1995 5.0L)
• 4R70W 4 Speed W/Overdrive (1996-1998 4.6L 2V)

S197 (1999-2014) Auto Transmissions

• 4R70W 4 Speed W/Overdrive (1999-2004 4.6L 2V)
• 4R75W 4 Speed W/Overdrive (2003-2004 4.6L 4V)
• 5R55S 5-Speed W/Overdrive (2005-2010 4.6L 3V)
• 6R80 6-Speed W/Overdrive (2011-2014 5.0L 4V)

S550 (2015-2018) Auto Transmission

• 10R80 10-Speed Automatic W/Overdrive

For newcomers, overdrive might sound like this big crazy add-on that makes a car go super fast. How many sci-fi movies have we seen where they slap a vehicle into “overdrive” and rocket off? While overdrive is an amazing thing, it’s not exactly what you may believe.

Overdrive is a gear ratio higher than anything that is 1:1. Having the higher gear allows for the engine to keep the vehicle up to speed without overworking itself. This improves fuel economy and, of course, helps reduce wear and tear on the working parts. Sure, overdrive helps raise top speed on paper, but it’s not exactly some maximum force adder. It’s still extremely desirable for any car found on the highway for prolonged periods of time.

Manual transmissions get all the love. They get the sweet Hurst shifters, fancy knobs, and even tougher clutch assemblies to help with spirited driving. This doesn’t mean automatic transmissions can’t be upgraded though. For as long as racing has been around, automatic transmissions have been found in all sorts of race cars.

Naturally, hot-rodders would dream up ways to seriously modify automatic transmissions to stand up to the test. Sure, in order to increase the power threshold of the transmissions, one would have to look for someone to modify internal workings, just like a manual, but torque converters, shifters, and shift kits can be had fairly easily and will help your Auto-Mustang power through gears.

Flexplates are a defining characteristic of automatic transmissions. They are commonly, incorrectly, referred to as flywheels as they are very similar in appearance.

The truth is they serve very different purposes. A flexplate is called as such because it does exactly that, it flexes as the engine travels through RPMs to help out with proper shifting. If you want to start upgrading a Mustang’s power output and improve the shifting capabilities, this will need to be addressed.

Aftermarket flexplates are usually a lot lighter than factory equipment and can take a lot more abuse. If you’re upgrading the torque converter, you might as well swap in a flexplate while you’re at it.

Torque converters serve an important part in an automatic transmission’s function. Namely, it helps the transmission shift at specific RPMs. Right there you can already tell this is a great place to start making upgrades to your automatic transmission. A torque converter's “stall speed” is the rpm at which the converter achieves a hydraulic lock, the point at which the car has to move or cause the engine to stall.

High stall torque converters are great for launching. The higher stall allows the engine to rev to a higher RPM without shifting into gear. Obviously, the higher the RPM at launch, the faster your Mustang can accelerate.

In the past, high stall torque converters were not the greatest thing to have in your daily driven streetcar. They would cause your Mustang to be in a constant state of slippage since the stall speed would be higher than the actual rpm needed to maintain the car's speed on the road. Because of the advent and widespread usage of “lockup” type torque converters, this slippage is a thing of the past at cruising speed. A lockup torque converter has a large clutch plate inside that is applied by hydraulic pressure in the higher gears as directed by the powertrain control module, effectively locking up the torque converter and making for a solid connection between the motor and transmission. This means you can have your cake and eat it too. You get the high stall torque converter for those great launches at the drag strip as well as the lockup feature for the improved efficiency and mpg at cruise speed. We can all thank the fuel economy gods for this torque converter improvement.

Choosing the correct high stall torque converter for your Mustang makes a difference. In many instances, there can be a half-second or more drop in your quarter-mile time. It would take a great deal of engine modifications to match the performance improvement that the high stall torque converter is capable of providing. Getting the correct stall speed to match the power curve of the motor is critical to maximizing performance. You want a converter that has a stall speed where the engine is getting to the meat of its powerband. Somewhere in the area of 500 to 750 rpm below the torque peak for a max performance application is ideal. A street application can go for something more sedate if you rarely see the drag strip.  

Something else you must consider is to make more heat, so it is a good idea to add a transmission oil cooler. This is a simple thing to do and there are many available kits that will more than compensate for the added heat. All in all, a good high stall torque converter can be one of the best performance modifications for your automatic transmission equipped Mustang!

Shift kits are dedicated to manipulating the way the automatic transmission shifts as well. What’s important to know is having complete control over what your Mustang is doing is crucial to precision driving.

Equipping the automatic transmission in your Mustang with a shift kit gives you just that. Manual valve bodies are likely the most popular type of shift kit for older transmissions as they allow you to run through the gears manually, shifting once the engine has reached its peak power output.

Older transmissions like C5s will require being taken apart for you to install a shift kit. Newer transmissions like what will be found in S550s or S197s can have the shift points manipulated with custom tuning, which saves you from having to get dirty.

Factory shifters can feel rather clumsy when trying to hammer through gears with an automatic transmission. Sure, they may look more natural in a Mustang’s stock interior, but they still don’t always feel natural.

Again, this is an area where S550 Mustangs may not need too much work considering the factory setup is pretty well equipped for spirited driving.

Other generations of our favorite pony car can benefit from aftermarket shifters especially if you’ve done other transmission upgrades. They make ease of gear selection for rapid succession through the gears.