Is the 6R80 an option?

[askiles]

I am planning my MKIV build right now, and will most likely do a Coyote backed by an automatic transmission...don't flame me. LOL Has anyone tried or successfully installed a 6R80 into the Roadster? I know the 4R70W will work...but a 6 speed auto would be nice. If anyone has, please do share! Thanks!!

[Alan_C]

I am putting a 2nd Gen Coyote and 6R80 into a 70 Mustang Mach 1. I cannot help you with to determine if it will fit in a MK4, but I am willing to assist you with measurements, pics, etc. if that will help you at all.
I will say the 6R80 is a big SOB as I had to modify the tunnel and firewall to make it fit in my Mustang.
Having owned a MK4 with a 4.6L DOHC engine and T3650 5-speed, I would suggest the 6R80 is bigger. The closest manual transmission in size would be the T56 Magnum. I understand that the T56 has been used before. The 6R80 uses a slip joint incorporated into the driveshaft, so the transmission itself is shorter than most modern transmissions. The issue is it is wide and tall. I will suggest if you can weld, then you can make it fit. You will not have the issues of a tight footbox as there is no clutch pedal. An interesting project and a excellent choice of transmission if you can make it fit. I should have my Mustang up and running in about a year.
Feel free to reach out to me via PM if you have specific questions.

[askiles]

Thanks! Yes, the welding capability is there. It will be a must. I know I will have to make a transmission mount specific to the 6R80. Luckily it is shorter, I am just not sure it is short enough. I spoke to Denny’s Driveshaft about the slip style driveshaft, and what the shortest was that they could make one, that may be the crux of it. The Roadster is short wheelbase and takes a very short driveshaft, of which may be too short to make a slip driveshaft. I may need to research lengths of driveshafts of various transmissions, and compare them to the lengths of the 6R80 and determine if it will work. I think this is the one factor that may hold me back from using the 6R80 and instead going with the 4R75W.

[Alan_C]

svtfreak here is build a hot rod truck with the 6R80 and supercharged Coyote. He may be your best source of information here on what does and does not fit.
I had Denny's source my driveshaft. They make a high quality product, just not cheap or quick to deliver. I can likely estimate the minimum DS length from my DS. I will take a look tomorrow and post my best guess. At least with a good guess at the length, you will know if it is possible. If my minimum is longer than the space you have, then SOL I guess.

[Alan_C]

Sorry about the delay, distracted by other things. I took a measurement and as best I can suggest, the minimum DS length would be 20 inches. If that is close, you are golden. However, before making a final decision, I would discuss with Denny's to determine if they agree. I allowed for 1 inch sleeves to be used to join segments.
Good luck

[Bob Cowan]

You will probably have to modify the trans tunnel a little bit - it's a wider trans than others.

You will also need to fabricate a rear trans support. Not a big deal.

Get a stock Mustang drive shaft, and have it cut down. You need the tringle connector to the trans. Again, not a big deal.

The stock torque converter has the wrong stall speed for such a light car. You'll need to replace that as well. Not cheap.

You cannot use the stock Mustang shifter. It sits too far back on the tail shaft. There are a couple of shifters on the market specifically for the 6R80. Or you can use any 3 speed cable shifter, and modify it for 2 gears.

The stock Mustang rocker switch has gotten hard to find. There's a few available, but you might have to hunt for it. Or you could get one from the bone yard.

The ECU controls the transmission. Make sure you have an ECU for an auto car.

[Alan_C]

Yeah Bob is right, you can likely repurpose the Mustang driveshaft if you have a good DS shop in your area.
Here are the transmission mount components I used installing the 6R80 in my 70 Mustang. Or you can adapt parts you can obtain at a junkyard. It is up to you trading off new vs fabricating your own.
https://totalcontrolproducts.com/c-1...on-mounts.html
There are aftermarket controllers for the 6R80, so if you bought a Control Pack for a manual transmission, you have a way out.
The engine harness for use with the 6R80 is different. You can buy a AT compatible harness for a few hundred bucks if you have an engine from a manual transmission car. My guess would be that all crate engines are meant for manual transmission applications, check with Ford Performance to be sure. Even if Ford made a crate engine for use with the automatic, it is likely few resellers have one. I know Ford sold a crate engine and 6R80 transmission combo at one time. I remember as the price of around $17K sticks in my mind. I sourced my engine and transmission from a Mustang GT bought at auction and saved a lot of money doing so.
Holley has their Terminator X ECUs now that include the transmission controls as an alternative to the FP Controls Pack.