2015 Mustang GT rear axle source

[BobCarter]

In order to build a MKIV with the new FFR IRS, I need a source for a complete 2015 Mustang GT rear/gear setup. (Not just the ring and pinion). I have searched my local salvage yards, the web, and went to my local Ford dealer. I can purchase all the parts to build up the unit (from the Ford dealer and pay them to put it all together) but I prefer a source from whom I can purchase one fully assembled and ready to install. Does anyone have a source?

[Jeff Kleiner]

Ford Motor Company will be supplying Factory Five with all-new Mustang centers, spindles, and brakes in the near future, and we will be selling these factory-new parts at an attractive price.

I'd give FFR a call to find out the details.

Jeff

[edwardb]

Interesting timing. I talked to Factory Five a couple days ago. I officially changed my 20th anniversary Roadster order to a Coyote. :D During the call, I asked if there was an update about availability of 2015 Mustang IRS components from Ford. In the news release about the new IRS it's stated new Ford components would be available from FFR for an "attractive price." The response I received this week was no word from Ford and no update. I then asked if there was any estimate of the costs, since that was kind of an open item for my build budget. And a scary one if I might add... The advice I received was to look for the parts in salvage. Would be cheaper plus how many miles or wear could be on 2015 parts? So that's what I did. Started looking. It didn't take long to find them at MPS Auto Salvage in Georgia. They are a forum vendor over on the other forum, and I found numerous positive comments about dealing with them. They have complete 2015 Mustang IRS pallets. The complete assembly is in a cradle and drops off the chassis by removing a few bolts, the shocks, and the driveshaft. They aren't selling the individual parts, only a complete assembly. They had what I was looking for -- 3.55, posi (they all are), cast iron diff -- so I ordered it. The price I got was pretty good, IMO, and I'm hoping to sell all the unneeded parts (axles, CV joints, control arms, cradle, etc.) to offset some of the cost. Could turn out to be pretty reasonable, especially considering some of the costs I'm seeing guys pay for the older stuff. The great news is these are zero mile take-offs. Brand new, undriven. They are apparently from an aftermarket production line where factory Mustangs are upgraded with a Roush engine, new IRS assembly, plus some other changes. I am planning to post more information and pics when it arrives. It's coming by truck as of yesterday. BTW, I told the guy at MPS that Factory Five was changing over to the 2015 Mustang IRS setup. He said he did a lot of business with Factory Five customers but this was new information for him. I told him to expect more calls about the new IRS.

[tirod]

Went on a search this morning after reading the F5 email trying to discover some more info about the diff. So far all I can find is it's an 8.8 with 34 splines. Apparently there are other changes - obviously enough to warrant a complete redesign of the control arms to use the newer stock hub carriers.

Any links to an analysis of it and how it's better? Nuts and bolts talk if you ask the right questions. And as for the handling, it's nice to hear that Mr. George says it's faster on the track than the previous 2000 version. We'd like to hear it expressed with numbers and his insights on transient handling etc.

I have no doubts 15 years has created improvements and F5 is taking advantage of them to the fullest. A lot of us will be wanting to know just how much better it is - helps to salve the costs when it's right there in the numbers, ride quality, and handling.

Thanks for the link to a supplier, Edward, new take out pallets are likely to be a hot item for builders as knowledge of the upgrade gets around. And, it's going to be asked - it's it possible to upgrade an older model? There's going to be some who will do it.

[CraigS]

That is great news. I hope one day to upgrade my MkII. My wife traded her 2010 Mustang GT on a 2015 GT w/ the Performance package 3 months ago. The difference between the 2 cars is unbelievable and a major part of that is the IRS. Anyone putting this into an FFR is in for a real treat.

[RRussellTx]

I just bought my knuckles for my 20th anniversary IRS off of eBay from seller racer91m - he said that he had 16 2015 IRS complete assemblies with various gear ratios. My knuckles should show up next week so I can't verify quality yet.

[RRussellTx]

I also found this link that shows the different gear ratio options available for the 2015 Mustang.
http://www.saac-mcr.com/main/2014/2015mustangUnveil/Mustang_Specs_USA.pdf
Looks like 3.15 3.31 3.55 and 3.73 were available.

Also, when I called FF - the tech said that the aluminum automatic would work too. I asked twice to be sure since the website stated otherwise and he confirmed. I would call and confirm yourself if you go with the automatic but it may be an option and it would be lighter too.

[edwardb]

I just bought my knuckles for my 20th anniversary IRS off of eBay from seller racer91m - he said that he had 16 2015 IRS complete assemblies with various gear ratios. My knuckles should show up next week so I can't verify quality yet.

I've been working on obtaining the necessary parts for the 2015 Mustang IRS pretty much since I ordered one of the 20th anniversary Roadsters, as I described in my earlier post. FF has only said you need the LH and RH knuckles, without being very specific. But in looking at the parts list FF provided in the IRS announcement, it seems the hubs and bearings are also required as part of the knuckle assembly. I was going to respond to your post saying you need the hub and bearing in addition to the knuckle. But I see by looking at racer91m's eBay listing, looks like that's what he's selling. One observation though. If that's what it is, e.g. knuckles FR3Z-5B758-B (RH) or FR3Z-5B759-B (LH) and the hub assembly FR3Z-1104-B and studs and bolts, the eBay listing price is higher than the individual parts cost for one assembly. Maybe I'm missing something though.

Another sort of related observation, and hopefully I'm getting this right because this IRS thing is all new to me. For the older design Ford IRS knuckles, it seems the rear axle bearings were pressed directly into the knuckle itself. Lots of posts and threads about getting them out, back in, etc. The new design appears to have the bearing in a separate carrier that is bolted into the knuckle. Hopefully this will be easier to maintain? We'll see soon enough. I'm sure there will be other differences.

[RRussellTx]

I'm trying to figure it out too! That's why I went the safe route with the full knuckle assembly. What I can't figure out is the spindle. I see the parts you listed, but in the pics there is clearly a nut to hold the hub to the spindle but I don't see the actual spindle in any of the online parts listings/schematics. Looking forward the parts showing up soon.

[edwardb]

I'm trying to figure it out too! That's why I went the safe route with the full knuckle assembly. What I can't figure out is the spindle. I see the parts you listed, but in the pics there is clearly a nut to hold the hub to the spindle but I don't see the actual spindle in any of the online parts listings/schematics. Looking forward the parts showing up soon.

The CV axle (shortened version included with IRS kit from FF) goes through the hub assembly (splined) and is held in place by a CV6Z-3B477-A axle nut. Don't see the axle nuts listed on the FF IRS kit. Not expensive, and supposedly one time use. On the old IRS design, the axle nuts take a 36mm socket and are supposed to be torqued to 250 ft-lbs. I'm expecting these to be similar, but will find out.

I bought the whole assembled IRS pallet, as indicated previously, and expect it to be here sometime this week. Hope to learn more seeing how it's assembled from the factory. BTW, I see the place I bought my complete assembly (MPS Auto Salvage) is now selling just the pumpkin. New listing on eBay. They weren't selling individual parts when I talked to them last week. Looks like they're realizing there's a market out there.

[RRussellTx]

Makes perfect sense - thanks for clearing that up!

[RRussellTx]

Well, My center just arrived from MPS Auto Salvage today and one of the bolts they left in was cross threaded badly. They did not package the 100 lb unit very well so it could have been caused by shipping - but either way it is not usable until I get that worked out. I'll let you know if they help make it right but if you have a center shipped I would ask them to remove the bolts and package it properly first.

[edwardb]

I also found this link that shows the different gear ratio options available for the 2015 Mustang.
http://www.saac-mcr.com/main/2014/2015mustangUnveil/Mustang_Specs_USA.pdf
Looks like 3.15 3.31 3.55 and 3.73 were available.

Also, when I called FF - the tech said that the aluminum automatic would work too. I asked twice to be sure since the website stated otherwise and he confirmed. I would call and confirm yourself if you go with the automatic but it may be an option and it would be lighter too.

Good information. I saved that document with all my other build files. Yea, FF told me the same thing when I called. Said I could use an aluminum center from an automatic if I wanted to. Said that, per Ford, they were limited to 500 HP, and that was in a 4,000 lb car. So should be fine in our lighter cars especially if we don't exceed that HP. Said they required a different length driveshaft, that's where there are two listed on the 2015 Mustang IRS order form. Also said they were roughly 36 lbs lighter. That's quite a bit I guess, but not a deal breaker for me. I decided to stay with the cast iron to eliminate any variables since all the previous information was so specific about it. Just not something I want to get wrong. Plus, they didn't have an aluminum center in the 3.55 ratio I was looking for.



Well, My center just arrived from MPS Auto Salvage today and one of the bolts they left in was cross threaded badly. They did not package the 100 lb unit very well so it could have been caused by shipping - but either way it is not usable until I get that worked out. I'll let you know if they help make it right but if you have a center shipped I would ask them to remove the bolts and package it properly first.

Sorry to hear that. Since you bought only the center I assume it's one of the chassis mounting locations that was damaged? If it's cross threaded, hard to imagine that's shipping damage. Will be interested to hear how this gets resolved. I'm still waiting for a call from Conway for my complete IRS pallet.

[RRussellTx]

Sorry to hear that. Since you bought only the center I assume it's one of the chassis mounting locations that was damaged? If it's cross threaded, hard to imagine that's shipping damage. Will be interested to hear how this gets resolved. I'm still waiting for a call from Conway for my complete IRS pallet.

Yes, check out eBay Item # 121694218962 from mpsautosalvage. They left those steel bolts sticking out of that aluminum rear cover (FR3Z-4033-D). I also thought it had to be damaged before shipment but they put that 16X18X12 pumpkin in a 20X20X26 cardboard box without any packaging material and let FedEx ground have their way with it. I can see how that steel bolt could strip the half inch of aluminum threads if it was hit wrong. Worst case I'm out $100 bucks for the new rear cover. Hopefully they will help me out somehow.

43426

[RRussellTx]

Here is another link that I found useful and might be relevant for this thread.
http://www.tremec.com/calculadora.php - It's the Tremec Gear Ratio Calculator.

The 18" Halibrand Style Replica Wheels on my 20th Edition run 315/30 ZR18s which has a 25.4 inch Tire Height (Googled 'tire height calculator' to figure that out).
I'm looking at the TKO-600 with the .64 Overdrive. I picked the 3.31 as it gets me 71mph at 2000 rpm - I figure that's my cruising sweet spot for the open Texas roads.
It's also not that much different than the 3.55 at moderate to high RPM's in the lower gears.

Anyway, I just thought I would post my logic in case others found it useful.

[edwardb]

Yes, check out eBay Item # 121694218962 from mpsautosalvage. They left those steel bolts sticking out of that aluminum rear cover (FR3Z-4033-D). I also thought it had to be damaged before shipment but they put that 16X18X12 pumpkin in a 20X20X26 cardboard box without any packaging material and let FedEx ground have their way with it. I can see how that steel bolt could strip the half inch of aluminum threads if it was hit wrong. Worst case I'm out $100 bucks for the new rear cover. Hopefully they will help me out somehow.

43426

Ouch. Google the rear cover part number FR3Z-4033-D. $60-70 bucks a number of places. Just looking at the pictures of the IRS setup in the chassis, those rear mounts look like they're in pretty well supported chassis bushings. Maybe it could be saved. Helicoil? Sure didn't have to happen though.

[RRussellTx]

Well, it looks like mpsautosalvage is going to hook me up with a new rear cover to make it right.

I also received my knuckles and hubs from racer91m today. Packaging was good and they look like what I need. Here is a pic so you can see what I got and maybe let me know if you think it's what we need.
43450

[edwardb]

Well, it looks like mpsautosalvage is going to hook me up with a new rear cover to make it right.

I also received my knuckles and hubs from racer91m today. Packaging was good and they look like what I need. Here is a pic so you can see what I got and maybe let me know if you think it's what we need.
43450

Just got the knuckles and hubs off the complete IRS assembly I purchased. Look just like yours! I will be interested to see if the FF setup uses the rubber bushings already pressed into the knuckles. They look like they'd be pretty hard to get out. Glad MPS is taking care of you on the diff cover.