Mustang Donor IRS ?'s

[JIMLAND]

Planning on ordering my MK4 kit sometime this year and would like to install a rear IRS. Looks like I could save quite a bit of money if I could find a good salvaged 2015+ Mustang IRS 3.31 Rear End Drop Out. Sounds like if I do this I can use the differential, spindles, hubs, brakes and rotors. Is this correct? The ones I have found for sale are salvaged units that have 10,000 - 20,000 miles on them and far enough away I can't go look at it before buying so have to rely on pictures and description. I've heard sometimes you can find a new drop out but haven't yet. Any tips on what to look for or look out for when searching for one? What would be a good price for one of these salvaged units?

[boBQuincy]

I am planning to do the same, it looks like most wrecks are primarily front end damage and most of the IRS parts should still be like new at 20,000 miles. Some choices are iron or aluminum diff housing (FFR tech says either is ok); what size and type brakes. Although all GTs are supposed to have vented rotors I saw an assembly with the iron housing and non-vented rotors, not supposed to exist?

I am looking at the photos for any damage, other than anything obvious we are guessing that it is ok. Someone on the forums had to buy a new spindle, about $250. Prices look to be around $500 to $800 for the entire assembly, pretty good savings over ordering all the parts new.

[mach'er]

As you are looking at donor S550 parts, consider Misterfubar's experience with regards to the rear factory IRS brakes - depending on what wheels your looking at and/or what mods your willing to make.

http://thefactoryfiveforum.com/showt...ng-rear-brakes

I went the new parts route, and now have ~$450 worth of factory rear brakes that are apparently not going to fit in the 17" Halibrand replica wheels I ordered with my kit (without making modifications). I don't have first hand confirmation of the problem, because I'm not to that point yet - but I thought it worth pointing to that thread. I missed it during my planning stages.

Thanks do go out to Misterfubar. Sorry that happened to you, but thanks to your thread, it was caught before I ended up with the same stripe on the inside of my wheels.

[edwardb]

I am planning to do the same, it looks like most wrecks are primarily front end damage and most of the IRS parts should still be like new at 20,000 miles. Some choices are iron or aluminum diff housing (FFR tech says either is ok); what size and type brakes. Although all GTs are supposed to have vented rotors I saw an assembly with the iron housing and non-vented rotors, not supposed to exist?

I am looking at the photos for any damage, other than anything obvious we are guessing that it is ok. Someone on the forums had to buy a new spindle, about $250. Prices look to be around $500 to $800 for the entire assembly, pretty good savings over ordering all the parts new.

Thoughts from my side on this subject. I was lucky to find a zero miles new take-out 2015 IRS pallet for my build. 3.55 iron case center section. The supply of new take-outs seems a bit sporadic, but worth checking. Mine came from MPS Auto Salvage in Georgia. Seems to be a pretty big player in the Mustang salvage market. I had the Wilwood brake option with my kit, so didn't need the Mustang brakes. Good thing. MPS didn't include them with my pallet. Shipping for the complete pallet from Georgia wasn't cheap, and I had to pick it up at the freight terminal to avoid an additional liftgate charge. I thought the parts I didn't need (upper/lower control arms, CV axles, IRS cage, etc.) would have some Craigslist or eBay value. Basically they didn't. I made < $100 after a lot of work packing and shipping, and never did sell the IRS cage so had to throw it away. At the time I was putting my kit together, the new IRS components weren't available from Ford. They are now. The non-Torsen center sections are around $900. The knuckles about $250 each. That's for NIB parts. Shipping isn't going to be crazy expensive and you won't have parts to dispose of afterwards. If you don't need the brakes, definitely something to consider IMO.

One other thing to consider. I just looked and there are several salvage IRS pallets on eBay in the $500 - $800 range. Shipping isn't included so that's something to check. But note that 3.15 ratio setups are cheaper than the rest. Probably the reason is there is a difference between the 3.15 center section and all the rest. I don't know the specifics other than the ratio can't be changed from 3.15. All the others (3.31, 3.55, 3.73) will accept ratio changes. If a 3.15 fits your needs, could be an economical choice. Just realize it can't be changed. Also note the stock 3.73 as part of the Performance Package is a Torsen setup. So they are basically twice the price of anything else. This chart shows the various combinations and brakes that come with each. https://media.ford.com/content/dam/f...tang_Specs.pdf

[CraigS]

As you are looking at donor S550 parts, consider Misterfubar's experience with regards to the rear factory IRS brakes - depending on what wheels your looking at and/or what mods your willing to make.

http://thefactoryfiveforum.com/showt...ng-rear-brakes

I went the new parts route, and now have ~$450 worth of factory rear brakes that are apparently not going to fit in the 17" Halibrand replica wheels I ordered with my kit (without making modifications). I don't have first hand confirmation of the problem, because I'm not to that point yet - but I thought it worth pointing to that thread. I missed it during my planning stages.

Thanks do go out to Misterfubar. Sorry that happened to you, but thanks to your thread, it was caught before I ended up with the same stripe on the inside of my wheels.

I asked in your thread where you got the idea they wouldn't fit but see it here. Did you read to the end of the thread you linked? He solved his fit problem w/ 1/4 inch spacers and longer studs. Seems like a fine low cost, easy to do, solution to me.
BTW a freidn bought a 2015 salvage unit w/ what we think are V6 brakes because of the solid rotors which are a little smaller OD. We compared to mine. We were doing this somewhat unscientifically be cause we didn't have any lugnuts for the stock 2015 studs. But, as best as we could visually center the lugs in the wheel holes it turns out that the V6 brakes offer no advantage. Really weird as the rotors are smaller, but the calipers are enough thicker that there is no, or an extremely small, advantage as far as wheel fitment.

[jcrumpley]

The 17 inch Halibrand replica wheels will fit on the 2015 mustang 13 inch IRS brakes with some slight clearancing of the calipers. Just use a grinder or a file. Mine mount fine now without any spacers.

[kcp1989]

This is exactly what I needed to know, thanks for being the guinea pig!

[chuckster]

I just bought a 2015 rear IRS setup from the parts farm, an eBay seller out of Georgia. 11000 miles , gt 13" brakes, cast iron center section with 3:55s. $849 shipped. The boys at FFR said that was a good deal. Delivery is scheduled
For tomorrow, Ill post my impressions here tomorrow night.

[GKindle]

I bought a complete rotor to rotor 3.31 cast iron IRS from a 2017 Mustang GT from Midway Mustangs in DeWitt, Iowa. The unit only had 161 miles and the cost was $700.00. I picked mine up at their shop, but he ships daily.

[Connedale]

If I just buy the center section and spindles, can I use my 1998 Cobra rear brakes with this setup? It seems like my braking would be better balanced using the 1998 brake parts. It would be less weight at least.

[Connedale]

Any ideas on if 98 Cobra brakes will work?

[edwardb]

If I just buy the center section and spindles, can I use my 1998 Cobra rear brakes with this setup? It seems like my braking would be better balanced using the 1998 brake parts. It would be less weight at least.

Any ideas on if 98 Cobra brakes will work?

Based strictly on pictures, won't seem a direct fit. At the very least, the distance from the mounting points to the hub looks quite different. A call to Factory Five or someone who works with these a lot like Gordon Levy might get you a more definitive answer.

Cobra rear brakes:


2015+ IRS setup:

[Connedale]

At worst case, if Mr. Levy does not have a solution, I could design a spacer, correct? It looks like it would be a simple waterjet part with reamed holes made from aluminum plate to me?

[CraigS]

If I just buy the center section and spindles, can I use my 1998 Cobra rear brakes with this setup? It seems like my braking would be better balanced using the 1998 brake parts. It would be less weight at least.

I don't understand your reasoning here. A salvage rear complete w/ brakes will be less than the cost of the parts so why buy parts and then hope your 98 brakes will fit. What if they don't? Now you need to buy 2015 brakes as separate parts. My experience is that the 2015 brakes work very well.