Needing some IRS recommendations

[BRRT]

Hey guys,

I'm in the market for a 2015 (or newer) Mustang IRS dropout. Any recommendations on a source? How about the best year if I come across a choice? Are all of the brakes the same, or are some years/option packages better than others? Will the aluminum housing hold up, or should I focus my search on the iron housing? I'm thinking a 3.55 ratio, clutch type limited slip.

Thanks for any info.

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Jeff

[toadster]

hit up Mike Forte at Fortesparts.com I got my IRS rear from him and the knuckles - FFR can supply them as well

I believe any 2015-2021 IRS should work and get the 3.55 setup that should work best depending on your desired results, not too crazy on the upper RPMs on the highway, but also not too low to lug the motor

[edwardb]

Couple of responses based on my experience. New parts are of course available. They're catalog items from Ford Performance. Same as what Factory Five offers. Don't know about Forte. The standard offering is an iron case 3.55 ratio standard Trak-Loc setup. Most common and will work for many builds. The knuckles/hubs are the same for all (M-5970-M) and just over $500 new. Could argue best to start new to get new bearings, etc. but salvage could yield serviceable units. For my first IRS build, I purchased an entire IRS palette, thinking I could recover some of the cost by selling all the parts I didn't use. Turned out not to be the case. The Mustang specific suspension pieces just don't have much market value and the extra shipping cost for the entire palette wasn't a good value. Your experience could vary, but don't expect for the leftover parts to be much more than recycle. When the newer 2015+ IRS was introduced, Factory Five said only to use the iron case. Later changed to either iron or aluminum. So either is fine and I've heard zero reports of issues with either. They're very robust and our cars are much lighter than a Mustang so hold up fine. The center sections are widely available in salvage, Ebay, etc. Just search and you'll find them. As already stated 3.55 is the most common and would be a safe bet. But other ratios could work depending on your build plan, intended use, etc. I would avoid the 3.15 ratio. They're generally cheaper but for a reason. They're the only ratio that can't be retrofitted to a different ratio. 3.15 can work for some builds, and guys have definitely used them. But something to be aware of. You'll also find Torsen lockers available vs. the standard clutch pack lockers. Interesting for our builds (I have that in my Coupe) but typically the cost is much higher and many don't want to pay for it. Can't help you with brakes because I've only used Wilwoods. But lots of value there too with the right parts. Good luck.

[CraigS]

Some of the ratio decision depends on what engine you will have. I had one of the 315s because it wasn't as expensive and I didn't realize it can't be swapped. It worked out fine though because my 408 was a mild build w/ plenty of torque.

[BRRT]

Thanks for the info. Very helpful!

[racingandfishing]

I wanted a torsen for my upcoming build and they are no longer available from Ford Performance. Got lucky and found a 3.55 with 20 miles on it from a 2021 Mustang that had front end damage that looked to have occurred in transport as the car was still in wrappers. It was from an automatic car and has the iron housing (I think all torsens have the iron housing, but could be wrong).

I sourced it from LKQ online. I've bought other parts from them in the past and had good luck. They offer returns and warranties on most items. They also have pics of the donor car. For me, I just try to avoid any with damage to the area of the part I am looking for, in this case damage to the rear.

Looks like they have several torsen 3.55's and 3.73's right now with various mileage and prices. Depending on where you live, there may or may not be freight as they will transfer parts within a given region at no cost.

As far as the spindles and knuckles, I found the Ford Performance kit (M-5970-M) to be cheaper as LKQ only sells it similar to a drop out less the diff with parts I didn't need or want. Plus the kit is brand new.

Best of luck with your build!