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This is a long read… but i have these conversations many times each week, so I’m trying to provide this info to educate those interested in this swap.
Team321 has been designing custom IRS and making kits for factory IRS components for years. As mentioned above our original target IRS was the Lincoln Mark8 / Thunderbirds from the 1990s. We still produce mounting kits for these older 1990s IRS subframes, but since their availability is decreasing, we are constantly looking into the next big thing… and the Mustang IRS is the next big thing! The performance and cost is the best thing going right now.
Ford started equipping their Mustangs with Independent Rear Suspensions in 2015 and have been making quite a few of them to date… they are showing up in wrecking yards and make GREAT rear suspension upgrade for classic trucks and other vehicles. Think about the Coyote and Boss powered cars… These rear ends hold up to high HP / Torque and will be the Rear Suspension of choice going forward for many years.
Here is a picture of an IRS as you would get it from The Parts Farm in Lyons GA…. I have purchased 3 from them and they are great to deal with.
Team321 has been known in the Ford Truck community for providing TruckIRS kits for 10+ years with 4 – 500 kits sold using the 1990s era Thunderbird and Lincoln Mark8 IRS subframes. I would like to point out that at first glance, the new Mustang IRS subframes look very similar to the Tbird/Mark8 subframes but there are a few things that prohibit a simple $395 mounting kit to fit it to your truck. I want to go through those items with the hopes of educating those that would like to use this new platform and spawn any additional questions you may have…
The first few things you will notice is the input to the differential… not a traditional U joint, but Factory Five has an adapter – https://www.factoryfive.com/ I could not find a more direct source for the exact part, but talk to them… again, another great company to buy from.
The next thing you will notice is the separate Coil Spring and Shock. A coilover shock with a concentric spring is a better option since Coilovers allow you to select your spring rate and shock length… and to mount the shock that far outboard is simply not practical… so coilovers are the best solution… Team321 has Upper and Lower Coilover mounts… Both the upper and lower coilover mounts are bolt-in, so regardless if you use my mounting brackets or design your own, I have parts to help you easily meet your end goal. Team321 has designed around QA1 shocks for over 20 years and would be happy to help you select the right shock for you for your desired ride height.
When we looked into mounting the 2015 and newer Mustang subframe, the original goal is to create a kit that mounts the unaltered Mustang IRS subframe to meet up with Classic Truck frames with minimal to no modifications.
The IRS Subframe has four mounting locations… 2 FWD and 2 REAR mounts. I’ve spoken with Ford Engineers about this and during install on the factory line, the subframes are aligned, but the subframe mounts use 14mm bolts (around 9/16″) and the holes that the bolts fit in the subframe are around 1 1/4″ diameter… that’s a large gap between the OD of the bolts and the ID of the mounts… so I created some Nylon bushings to take up that gap.
After locating a Mustang IRS Assembly we position it relative to the truck frame rails. It is important to keep the suspension
Such a goal creates quite a few challenges… first of all is the resulting ride height. We will get to that later… let’s just say the “correct” ride height is like opinions.
On to the mechanicals:
The Mustang Rear suspension solution using the 2015 and newer Mustang IRS is complete, but I discovered a variety of things that may not be immediately apparent when you look at what’s involved.
The factory mustang IRS subframe has 1.25” mounting holes in the subframe and uses 15mm bolts to meet up with the Mustang unibody. Let me restate… The IRS subframe has 1.25″ (approximately) and expects a 15mm or 9/16″ bolt to adequately locate the subframe. That’s a huge gap… and it’s not acceptable to me… So I machined bushings to take up that gap. The inside diameter fits the mounting bolt… and the outside diameter fits the subframe.
Here is a pic trying to show the bushing sleeve.
The next thing you will notice is the factory Mustang coil spring / shock will not work due to the dimensions of your truck’s frame rail spacing… but this can be resolved with coilovers… and the associated upper and lower coilover mounts. I have noted that below… Now we need to mount coilovers to the lower control arm, this is easily accomplished with a special lower mount from Team321
And due to the position of the coilovers, the rear sway bar is impacted… which requires relocating the swaybar rearward… so I’ve added a pair of sway bar relocation brackets.
Mustang IRS install kit – $695 (2 FWD mounts, 2 REAR mounts, 2 Coilover mounts (upper and lower) and associated hardware + $57 shipping Continental US
For more information…Call (321)960-5945 or email dave@team321.com
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