IRS - Auto Trans Donor Question

[M22_COBRA]

I've got my eye on a dropout IRS complete 3.55 gear, spindles, brakes, hubs, etc. for my upcoming build.
It says it was out of a 2018 with an auto trans, but I'm looking at putting it in my car with a coyote and a TKX-600. Is there a compatibility issue I'm not aware of?
I cant see why it would be a problem but I figured I would ask.

[narly1]

All 2018 Mustangs used the 8.8 IRS axle, albeit in different gear ratios and differential types, and I believe that some (meant for use with smaller, lighter 4 cylinder engines) had aluminum vs cast iron differential cases.

So in my opinion as long as the axle ratio is appropriate for your engine/transmission set-up you're good.

Earl

[Jeff Kleiner]

Auto trans IRS is compatible however the manual and automatic versions use a different pinion flange. FFR will provide the correct adapter to couple the driveshaft to either; just let them know which one you’ll be using.

Jeff

[M22_COBRA]

Thanks! Forgot I read that somewhere else yesterday on the aluminum vs steel housings, maybe in the EdwardB 20th build thread I'm binge reading right now.
Makes sense.

[narly1]

Auto trans IRS is compatible however the manual and automatic versions use a different pinion flange.

Yes, I kind of forgot about that. The variable is going to be the driveshaft. As Jeff stated all you need to do is let FFR what your plans are for the engine/transmission/rear axle and they will sort you out.

Earl

[Hoooper]

The pinion flange changed sometime around 2018 and they all then became the same. Im not sure when it happened but I did research this about a year ago and found the measurements for the flange are all the same now. I just put a new aluminum diff in my car and it used the same adapter as the cast iron diff that came out. Aluminum diffs were only ever used in auto cars

[M22_COBRA]

Yeah copy that. I was just on another forum doing research and they had a great post with photos showing the difference pre 2015 to 2017+.
Sounds like it was to dampen a harmonic.

https://www.mustang6g.com/forums/threads/differential-flanges-any-experts.120933/

-2015-2017 Mustang with MT82 use 113mm pinion flange, 95mm bolt circle.
-2015-2020 Mustang w/ Automatic Transmissions use 110mm pinion flange, 93mm bolt circle.
-2018-2019 Mustang w/ Manual Transmissions use 110mm pinion flange, 93mm bolt circle.
-2015-2020 Shelby GT350 (Manual Transmission) use 110mm pinion flange, 93mm bolt circle.

[Hoooper]

For what its worth my kit came with the 110mm adapter so perhaps that is the standard size FFR has been including in the kits. A quick check in with FFR might get you an answer on what diameter adapter they are shipping.

[M22_COBRA]

Update:
I bought a thing today.... 2018 full rear irs asm, 31k miles, $1375 delivered!

189025