2015 Mustang IRS Components. So it begins.

[edwardb]

As I’ve mentioned in a few threads already, I ordered one of the 20th Anniversary Roadsters. These all will use the new 2015 Mustang IRS components along with a new rear suspension design from Factory Five. My kit is due in August, but I’ve been working to obtain the necessary Mustang center section and knuckles. FF announced they would make these parts available from Ford at an “attractive” price. But as of last week, they are not available and no pricing has been announced. At the recommendation of FF, I started looking for the parts in salvage. How much wear could 2015 parts have on them, anyway? Since this is all quite new, I thought others would be interested in more details.

What I found is that parts are out there as “zero mile takeoffs” from new Mustangs that leave the factory but then go to an aftermarket assembly line for further performance upgrades. The IRS assembly is on a subframe, and one of the common upgrades with a new more powerful drivetrain is to remove this entire assembly and replace with one that will handle the 600-700 HP engines, bigger and stickier tires, etc. Rather than re-using, these new IRS assemblies are being sold into salvage and are available. Strange IMO, but I’ll take new over used any time. MPS Auto Salvage, a pretty well known source for Mustang parts, has them available.

Last week I called MPS and they had just what I was looking for. A new zero miles assembly, the cast iron case recommended by FF, and the 3.55 ratio I’ve decided to use for my build. They offered the complete assembly to me for $1,350 plus shipping. It left Georgia last Thursday, and Conway called today for delivery. Turns out since my 2-car residential garage doesn’t have a loading dock (!!!) there was going to be an upcharge for a lift-gate delivery on top of the surcharge for a residential delivery. Since they were only 30 minutes or so from my house, I hooked up the SE and picked it up myself. Total shipping was $187. Not too bad for a 415 pound pallet from GA to MI. The IRS assembly was covered with cardboard, strapped to the skid, and everything stretch wrapped. All good. I used my shop crane to pick it out of the back of the trailer and get into the garage.

So here are some pics of the delivered IRS assembly. As best I can tell, it’s exactly what I expected. Everything looks new with no signs of any wear or shipping damage. There is a little surface rust on the cast iron case and the steel hubs, but not unexpected. The case will get a nice shiny coat of POR15 once I take it apart. My next step will be to remove the center section and the knuckles and get them ready for assembly to the new chassis. I've already backed out a number of the mounting bolts, and I was able to get the axle nuts loose. Obviously there will be a ton of parts I don’t need. I’m going to hang onto everything until the kit arrives and I make sure I have what I need. But then I’m hoping to make a few bucks off the unused parts. Seems that some of the parts should have some value, especially the CV axles. The subframe itself is a $900 part, but I’m not sure who might be looking for something like that plus wouldn’t be cheap to ship. No matter what, I think this is a relatively good value for what I received.

As delivered:





Center section waiting to be removed:

[edwardb]

Knuckle and hub assemblies, also waiting to be taken apart:









Interesting tag on the rear cover. No mention of friction modifier.



So now I’m up to four parts on hand for the new Roadster build. The IRS, the wind wings and visors I scored for 50% off at the FF Open House, and a new set of Harbor Freight horns. Don’t laugh. They work great and are cheap. I’ll be driving to FF to pick up the new kit hopefully in early August, based on my current production date. Then the fun really begins.

[BobCarter]

Well, i'm looking forward to receiving my shipment. Good to know about the last minute warning if my garage does not have a loading dock!
Everything in the photos gives me a sense of confidence. Keep us advised on your progress. I'll let you know how my delivery gores, should see it tomorrow or thursday. Thanks again for the tip on MPS. This takes the largest sourcing issue off the table.
:-)
BC

[2bking]

Nice find, and cheap for what you got. I assume when the upper and lower arms are removed they are replaced by FFR designs. I don't understand the lower A arm geometry that looks to put the A arm in a bind as it rotates through its travel. Otherwise, it looks to be a big improvement over the older design. BTW I don't see any tone rings for ABS. I wonder how ABS could be added if a builder was wanting to do so?

[RRussellTx]

Excellent - That is a great deal! I paid about $50 bucks more for the individual parts and I may or may not have everything we need...

BTW I don't see any tone rings for ABS. I wonder how ABS could be added if a builder was wanting to do so?

There is a spot to mount the ABS at the top of the hub but it looks like the tone ring is on the half shaft that will come with the kit.
IMG_0495.JPG

There should also be a tag on the bottom of the unit with the ratio mentioned (facing your pallet) - here is my 3.31 tag.
IMG_0487.JPG

[rmiller64]

Sure looks purdy Paul. Look forward to the build Let me guess next week will be that Coyote & TKO delivery

[edwardb]

Nice find, and cheap for what you got. I assume when the upper and lower arms are removed they are replaced by FFR designs. I don't understand the lower A arm geometry that looks to put the A arm in a bind as it rotates through its travel. Otherwise, it looks to be a big improvement over the older design. BTW I don't see any tone rings for ABS. I wonder how ABS could be added if a builder was wanting to do so?

Right. None of the OE arms are used in the FFR design. All new stuff in the kit. I agree the geometry looks a little unusual, but there's obviously a reason it's set up that way. No binding. It moves freely. What's not obvious is some of the pivots have some swivel to them. Not just straight bushings.

Regarding ABS, as RRussell said, there is a mounting point on the top of the knuckle for the ABS sensor and cable. The sensors came with my IRS pallet, but I had them out by the time I took the first pictures. I just took a picture of the knuckle with the ABS sensor in place, showing how it extends into the hub area. I also took a picture of the CV axle end that plugs into this area. Something different is going on here because you can see there aren't tone rings as in former designs. Just did some searching, and found that wheel bearings with a magnetic ABS pulse generator are now being used in some cars. Looks like that's what Ford did here. I believe it's the dark ring right under the tip of the ABS sensor in the first pic.

[edwardb]

Sure looks purdy Paul. Look forward to the build Let me guess next week will be that Coyote & TKO delivery

Slow down there big boy... Not planning any more purchases until the kit is here. That's my story and I'm sticking to it.

[edwardb]

Got everything apart already. Wasn't really that hard. Used a three-jaw puller to get the axles out of the hubs. Came off pretty easily. The CV axles popped out of the diff with a little bump from a crow bar, just like they're supposed to. Then took the diff out of the cradle. Will get everything cleaned up and that designer rust orange color of the diff painted gloss black with a POR15 treatment.

Note this picture also shows a pretty big design difference of the 2015 IRS knuckles compared to the older design. You can see the four bolts on the inside holding the bearing carrier in place vs. the pressed in bearings from the past.

[edwardb]

There should also be a tag on the bottom of the unit with the ratio mentioned (facing your pallet) - here is my 3.31 tag.
IMG_0487.JPG

Yep. My tag is visible in one of the earlier pictures I posted. Confirms it's 3.55.

[Jazzman]

How did you decide upon the 3.55 gear set as opposed to some other ratio? Even though I have not yet ordered my kit, I am thinking about following your lead and ordering one of these zero mile units while they are still available. I have decided to go with the coyote engine as well. I used the Gear Ratio Calculator that you or someone posted elsewhere on the forum. Tell me if I have these statements right:

1. The higher the gear ratio, the lower the top speed of the car, but the faster acceleration it can provide to get you there.
2. The higher the gear ratio, the more RPM you will have to use to achieve the same speed.
3. The lower the gear ratio, the better the fuel economy.
4. If the previous statements are correct, and my primary goal is cruising and long trips, (not road racing or drag racing), then a balanced, middle of the road approach would seem most prudent; a reasonable balance between acceleration and speed.
5. Since the Ford IRS comes in four ratios (3.15, 3.31, 3.55, and 3.73) it would seem that either 3.31 or 3.55 would be the prudent choices. I'm not sure how much difference there would be in fuel economy in either choice, and I'm really not sure I care!! I am certainly not building this to be an econo-car.

Therefore, I think that I have finally worked myself into the same conclusion you did. The 3.55 seems the best choice.

Ok, so how did I do? Did you use the same basic process, or did I miss something important? Thanks for your counsel.

[CraigS]

Jazzman you are correct. There are a couple of other things to consider. 1-what ratio is your 5th gear, 2-how much power will your engine have, 3-will that power be there at low rpm-say 2000- or will you have to zing it, 4-even if the power is at higher rpm, will the engine run along smoothly in 5th at 1500 or so rpm?

[edwardb]

How did you decide upon the 3.55 gear set as opposed to some other ratio? Even though I have not yet ordered my kit, I am thinking about following your lead and ordering one of these zero mile units while they are still available. I have decided to go with the coyote engine as well. I used the Gear Ratio Calculator that you or someone posted elsewhere on the forum. Tell me if I have these statements right:

1. The higher the gear ratio, the lower the top speed of the car, but the faster acceleration it can provide to get you there.
2. The higher the gear ratio, the more RPM you will have to use to achieve the same speed.
3. The lower the gear ratio, the better the fuel economy.
4. If the previous statements are correct, and my primary goal is cruising and long trips, (not road racing or drag racing), then a balanced, middle of the road approach would seem most prudent; a reasonable balance between acceleration and speed.
5. Since the Ford IRS comes in four ratios (3.15, 3.31, 3.55, and 3.73) it would seem that either 3.31 or 3.55 would be the prudent choices. I'm not sure how much difference there would be in fuel economy in either choice, and I'm really not sure I care!! I am certainly not building this to be an econo-car.

Therefore, I think that I have finally worked myself into the same conclusion you did. The 3.55 seems the best choice.

Ok, so how did I do? Did you use the same basic process, or did I miss something important? Thanks for your counsel.

I agree with these statements, as well as the comments from CraigS. For the Coyote, based on my experience plus the numbers from the calculator, either 3.31 or 3.55 would be the best choices. The final choice is most heavily going to depend on what final drive you select for the transmission, and also how you use the car. I had 3.55 in my Mk3 with a pretty warmed up 306 and a T5Z with .63 5th gear. It was just about a perfect combination. Nice and snappy, if not a little short in 1st. RPM at 70 mph in 5th was about 2,100, which was OK and about as low as that engine was happy with how it was cam'd, etc. For my current Mk4, I changed it up quite a bit. I'm doing 3.27 with a TKO600 and .82 final drive. The much stronger DART 347 carries the 3.27 just fine, and I really like the close spacing between 4th and 5th. There's not a big drop-off like in O/D ratios in the .60's. It's even usable in town driving in the 40-50 mph range. But I did give up a little for cruising. RPM at 70 mph is a little over 2,400. It's fine, and the engine is very happy there. I can slow down a bit, speed up, etc. without having to drop back to 4th. But probably giving up just a bit in economy, although that's not all that important. So kind of putting this together for the latest build, it will be a Coyote with a TKO600. The Coyote has somewhat less HP and torque than the current 347, so going back to 3.55 final drive to keep the "spirited" street cruising alive and well. I'm going with the .64 5th gear, which puts me back into a more pure O/D mode. The calculator shows 2,100 at 70 mph, which I'm fine with. The Coyote should handle that all day long. 3.31 with a .64 5th gear also shows good numbers. It would be slightly softer in the 1st - 4th gears, but 5th cruise at 70 mph would be around 1,950. Still easily handled by the Coyote, and probably slightly better fuel economy. But I just don't think it's a big difference, and I'll take the slightly quicker performance all around. My carb'd SBF engines are not known for economy. Now that I've got the DART 347 dialed in, it is getting 13+ mpg in mixed driving each time I've checked it, so it's not that bad actually. But I'm expecting the Coyote will be much better, especially at highway speeds. But as you said, we don't exactly have these for economy. Hope that all isn't too confusing. Either would be fine IMO.

[CHOTIS BILL]

Ok I am jealous. I do have one question which is what is the black link that looks like it goes from the outer bolt in the lower arm up to the top bolt in the knuckle. The only thing I can think of is it might be there to add strength to the knuckle but I doubt that is the reason. As far as adding friction modifier to the diff I believe I has a Torsen LSD and they don’t use it. On the lower A arm geometry it looks to me that the center line of the lower a-arm mounting bolts not being perpendicular to the center line on the car is to give it some anti-squat.

Thanks for all the info,

Bill Lomenick

[jceckard]

My guess for the ABS is the magnet is in the sensor. My bet is the four webs on the end of the half shafts (just above the splines) cause a pulse in the sensor when they pass by. Think guitar string vibrating over a pickup. Of course this is just a guess.

[edwardb]

My guess for the ABS is the magnet is in the sensor. My bet is the four webs on the end of the half shafts (just above the splines) cause a pulse in the sensor when they pass by. Think guitar string vibrating over a pickup. Of course this is just a guess.

Nope. I thought that at first too, but those tabs are a good 1/2 inch away from the ABS sensor when the axle is installed into the hub. I looked at it closer this morning. That dark ring I described before is clearly magnetic. You can observe it with a small screwdriver or knife blade. Check this video. https://www.youtube.com/watch?v=e32t-d32SEg

[jceckard]

Wouldn't the first time that I was wrong. Thanks for the clarification. If I were a cat, curiosity would have killed me a long time ago.

[FFRSpec72]

I would be so on this if we could get the challenge rules to change to allow an IRS like this, very nice.

[CHOTIS BILL]

After checking out the cad drawings and other pictures there are several changes made to the IRS which will account for the improvements mentioned. The first major change is the mounting of the spring /shock package. By moving them closer to the wheel and standing them upright will be a major benefit to their motion ratio. You can kind of thinking of it as the difference of trying to wright holding the pencil near the point or holding it near the eraser end. The next thing that caught my eye is the roll center seems to be raised which will make it happier to the front suspension, if the front suspension stayed the same. They also added a rear sway bar which will add adjustability which is always a good starting point. Once I get a car to handle properly I like to adjust the spring/shock package and front sway bar so that I can remove the rear sway bar to maintain as much rear tire compliance as possible.

Bill Lomenick

Another change for the better is the upper control arm has an added element to help take braking forces which the earlier one doesn’t have.

[edwardb]

After checking out the cad drawings and other pictures there are several changes made to the IRS which will account for the improvements mentioned. The first major change is the mounting of the spring /shock package. By moving them closer to the wheel and standing them upright will be a major benefit to their motion ratio. You can kind of thinking of it as the difference of trying to wright holding the pencil near the point or holding it near the eraser end. The next thing that caught my eye is the roll center seems to be raised which will make it happier to the front suspension, if the front suspension stayed the same. They also added a rear sway bar which will add adjustability which is always a good starting point. Once I get a car to handle properly I like to adjust the spring/shock package and front sway bar so that I can remove the rear sway bar to maintain as much rear tire compliance as possible.

Bill Lomenick

Another change for the better is the upper control arm has an added element to help take braking forces which the earlier one doesn’t have.

I'm 99% certain there are no changes to the front suspension. The anniversary edition has the higher end Koni shocks and the Wilwood brake upgrade. But no changes to the current Mk4 geometry. My understanding about the rear sway bar is that it's an available option, but not included as part of the kit. The connection points for it are all there though.

[edwardb]

Wrapping up the tear down and preparation for the 2015 Mustang IRS parts. Thought I would share a few more things. Got out the scale and weighed some of the parts. The knuckle and hub assemblies weigh 17 lbs each. The cast iron diff weighs 94 lbs all up. It wasn't easy to get the thing to sit still on the scale, but I think this is quite close. The fact that I can lift it (barely...) says this weight is in the ballpark. Multiple on-line sources cite the aluminum version is 24 lbs lighter, putting it in the 70 lbs range. Looking at some threads about the older design, appear both numbers are slightly heavier than before. But not much. Finally, even though I won't use them, weighed the CV axles. 43 lbs between the two of them. The new design is 34 spline at the diff, and 32 at the hub. Pretty meaty.

I managed to spill some of the fluid out the axle holes while moving it around. I'm just not smelling the quite distinctive odor of friction modifier. But the Ford instructions clearly state 3.2 pints (1.5L) SAE 75W-85 Premium Synthetic Hypoid Gear Lubricant and 4 oz. Motorcraft XL-3 Additive Friction Modifier. I'm planning to drain and replace the fluid as specified. This diff is a standard clutch-pack style limited slip setup. A Torsen setup is available only in the 3.73 ratio.

Several have asked if the internals are the same as past 8.8 diff, e.g. ring and pinion, bearings, etc. I can't answer specifics, but I'm guessing the answer is mostly no. In multiple searches, I found Ford referring to this new IRS diff as a "Super 8.8" touting its strength compared to past versions. I found a side-by-side pic of the new pinion gear compared to the old. The new is larger and longer. The slightly heavier weight compared to the past is also a clue.

Several have commented about the geometry of the new IRS, including the somewhat unusual looking links between the upper and lower pivot points. I compared the pics and knuckles now in hand with the pictures and drawings FF has provided of the new design installed. None of these short links are in the FF design. In fact, clearly one of the pivot points looks like it gets cut off the knuckles, as in the picture below. I won't be cutting anything until the kit and full instructions are on hand. But interesting.

[BobCarter]

Guesing there is no need to further disassemble the knuckle and hub ***'y?

[BobCarter]

Assembly

[edwardb]

Guessing there is no need to further disassemble the knuckle and hub assembly?

For now, I'm not planning to. The FF IRS parts lists has 10 wheel studs included. Required? Different threads or length? I don't know. If the old ones need to be pressed out and new ones pressed in, then some dis-assembly would be required. We'll see.

[karlos]

Interesting thread. The new IRS looks great, and at $1350 you got a smokin' deal. I have a MKIV on the way with the 'old' IRS. Sourcing the parts to complete the system was also what I first turned my attention to. I spent about $1550 just on the center section alone ($150 for a used center section out of a '94 Lincoln and $1400 for new innards plus labor to put it all together). The knuckles and hubs were another $650. So all told I'm in at about $2200.

For anyone contemplating IRS, you might want to jump on one of these zero-mile takeoffs before they're all gone. I doubt you'll ever find a better deal.

[edwardb]

For anyone contemplating IRS, you might want to jump on one of these zero-mile takeoffs before they're all gone. I doubt you'll ever find a better deal.

I doubt the zero mile takeoffs will be gone anytime soon. The aftermarket mods to new Mustangs is ongoing. But I have no doubt the prices could go up when the sellers see the marketplace demand. Just in the few weeks I've been at this, they've changed from only offering the complete pallet to now offering the individual components in total for more.

[rickscobra]

Seems as though FFR could get us a better deal from Ford. Time will certainly tell. I suppose Edward is correct, the time to buy is now.

[edwardb]

Seems as though FFR could get us a better deal from Ford. Time will certainly tell. I suppose Edward is correct, the time to buy is now.

I too will be very curious to see what the FFR deal is from Ford. What I did was a gamble, and I know it. As I described previously, exact prices for the new stuff that's required is hard to determine at this point. But looking at what parts are available, best I can tell the deal I came up with is around one half retail, if not more. Hard to imagine Ford will let them go through FFR for less than that, but we'll see. The other factor is when I first talked to MPS Auto Salvage a couple weeks ago, I mentioned that FF was switching to the 2015 Mustang IRS components for several of their designs. He said he did a lot of business with FF customers, but this was the first he had heard this. It wasn't long after that the individual parts starting showing up for sale. I don't think it's a coincidence, and if the demand is there, I think we all know what will happen with the prices. But just judging from eBay, MPS isn't the only one selling these take off assemblies.

What I can say is I've never been accused of being patient, so with my kit delivery just a few weeks away I wanted to have these parts on hand. I will also say that wrestling around a 400 lb IRS pallet is some work. I'm a solo act and also a grandpa. You do the math. Now that I have the necessary parts separated, not so bad. But I have a pretty big hunk of leftover metal and parts that hopefully I can get rid of and reduce the price even a little more. In the end, though, building one of these, especially the Anniversary Edition, is not a low budget exercise. So for those with delivery dates still a while away, it could make sense to wait. I think the zero take off option is going to be there as long as there are buyers for the upgraded performance Mustangs, and right now that market seems alive and well.

[karlos]

Anybody know what brake options are available with the 2015 IRS? Do you have to use the OEM brakes off the Mustang? I'm guessing the system as a whole is too new for Wilwood, etc, to have already produced much in the way of aftermarket options, but I could be wrong about that...

[Dragonfire]

The new IRS system should be awesome.

[edwardb]

Anybody know what brake options are available with the 2015 IRS? Do you have to use the OEM brakes off the Mustang? I'm guessing the system as a whole is too new for Wilwood, etc, to have already produced much in the way of aftermarket options, but I could be wrong about that...

The FF IRS announcement says that 2015 Mustang brakes can be used. No other OEM brakes mentioned. The 20th Anniversary announcement shows a Wilwood option that is used for those 20 kits, and says the Wilwood option will be offered separately.

[rickscobra]

Well, to the dozen of us that waited a little too long to order the 20th version, I think we should come up with a name for the, "20th Anniversary not so much" models. LOL September 24 seems like a long way away. Heck, we could have snow by then.

[BobCarter]

My IRS setup arrived today from MPS. looks just like yours Paul. Thanks again for letting us know about you find. This has a great impact on my budget $, and time. Really appreciate your sharing the info.

[edwardb]

My IRS setup arrived today from MPS. looks just like yours Paul. Thanks again for letting us know about you find. This has a great impact on my budget $, and time. Really appreciate your sharing the info.

Great! Glad it worked out for you. Now we just need a chassis to hang that stuff on.

[Jazzman]

Paul, What kind of warranty do you get on a "zero mile take off" IRS that you buy from MPS? You are certainly much more experienced than I at evaluating and restoring these parts. Was there any concern that all the rust might indicate enough neglect that there could be hidden issues? If I order one, I don't really expect to be able to "see" anything that might really be a concern. Caveat Emptor?

How difficult is the POR15 process, and how dangerous is it to the parts? How do you keep the cleaner from going where you do NOT want it to go? is sandblasting and powder coating a better long term solution?

Thanks!

[edwardb]

Paul, What kind of warranty do you get on a "zero mile take off" IRS that you buy from MPS? You are certainly much more experienced than I at evaluating and restoring these parts. Was there any concern that all the rust might indicate enough neglect that there could be hidden issues? If I order one, I don't really expect to be able to "see" anything that might really be a concern. Caveat Emptor?

How difficult is the POR15 process, and how dangerous is it to the parts? How do you keep the cleaner from going where you do NOT want it to go? is sandblasting and powder coating a better long term solution?

Thanks!

I'm not aware of (or expecting) any warranty beyond that it is what they say it is and arrives in advertised condition. Not unlike most salvage parts unless there is some agreement otherwise. MPS is a forum vendor over on the other forum, and as best I could determine, is a reputable source. I've never used them before, but my transaction went exactly as it should have and I would use them again if the need arises. I'm convinced the parts are exactly what they say they are. The IRS assembly shows little/no evidence that it's been driven, all the factory tags are in place and still very clean, etc. These 8.8 diffs are pretty tough, especially in our application where the vehicle weight is much less than in a Mustang. The risk of not having a warranty is low IMO. But everyone needs to do what lets them sleep at night. I expect the new parts from Ford, once they're offered, would have some kind of warranty.

Just to digress for a minute... I've been poking around on some of the Mustang forums learning about these parts plus sizing up what resale there might be for some of my leftover parts. As guys are upping the power on their new Mustangs, putting on sticky tires, etc. and running drag passes they are apparently popping axles pretty frequently. Multiple threads about this, and the various sources for aftermarket axles. I haven't found one mention yet of guys doing anything with the diffs or breaking them. This is with a 3,500 to 3,700 lb car running 10 second passes in some cases. I'm pretty sure they will hold up to our use.

The rust in the pictures is surface rust only, and is 100% normal for parts of this kind. The diff case is raw cast iron, the hubs are raw steel. They're going to get some surface rust almost from day one. It's possible that since they were taken off and transported around they may have been left out in the rain or exposed to high humidity (came from Georgia in the summertime...), but that's nothing to be concerned about. That's exactly the exposure they get in normal use under a car. Look under your DD, and you'll see the same thing. Look under brand new cars sitting on a dealer lot and you'll see the same thing. I'm going to clean up the diff and put some paint on it just because that's we do with builds like this. These parts are designed for the extreme exposure on the underside of a car, so they should be completely unaffected by any cleaning or painting. Within reason of course. I've already knocked most of the surface rust off the hubs, and don't plan on doing anything more. They are pretty much hidden once the suspension is assembled and the wheels mounted. They will get rusty again, but no matter.

I'm going to use POR15 because it looks good (almost like powder coating), it's extremely durable, and I happen to already have some gloss black on hand. They have degreaser and metal cleaner products I will also use, but nothing particularly special. Just like any paint job, the surface should be clean before application. They say to knock off any loose rust, which I'll do with a little sandpaper or wire wheel. POR15 paints pretty normally, although it does have a pretty strong smell and you don't want to get it on your hands or whatever. Hard to get off! The one negative about POR15 is that it's sensitive to UV light (sun). In this application under the car it will be fine. It needs a topcoat if it's going to regularly have exposure to UV light. But all this talk about POR15... you could just as easily use something like Rust-Oleum or similar from a big box store. It would be fine in this case.

Powder coating isn't necessary IMO, and I wouldn't want to be exposing the diff to the heat involved. Plus with the axles out, the diff internals are open to the outside. I have some rags stuffed in there and will exercise some care while handling. I wouldn't want to have any media or sandblasting done on them though.

One other comment. Factory Five specifically says on their website re: the new 2015 Mustang IRS to use the iron case differential, which is from manual shift Mustangs. But when you talk to them, they will tell you it's OK to use the aluminum case version. They're from automatic shift cars. No doubt the iron case is stronger, but they tech guys are saying the aluminum case is up to the task. About 25 lbs lighter and no rust. Another option guys can consider.

Hope this answers your questions!

[CraigS]

Edward can you tell what type of bushings/bearings on in the hub control arm mount points. I am hoping they are modern style and not the old rubber stuff like the old IRS.

[R Thomas]

In older manual transmissions high gear was direct drive 1:1 because it was believed to be most effective in transmitting power, however you might have noticed lately manufacturers have added 5th and 6th gears in the case of my Mustang both overdrive .80 and .60 in the pursuit of the all important mileage number. My car runs at 1200 rpm on the freeway doing 70 mph with its stock gears. So if you go to a 5-speed and spending a lot of time open highway cruising I would look for a rear for running in 4th at 1:1 and go for the wide gear .68 or so 5th for the highway.

[RRussellTx]

OK, I have some findings and a question.

Based on my research, it looks like all of the 3.73's are part of the GT Performance Package option that includes the M4204MT ($1,150 List Price on FordParts.com) Torsen Differential as opposed to the M4204M ($199 List Price on FordParts.com) LOK Differential.

From what I see, ALL of the 3.73's have the Torsen and ALL of the other gear ration have the LOK.
Also, the M4204MT TORSEN is compatible with the 3.31, 3.55 and the 3.73.

Soooo, does anyone know the difference between LOK and TORSEN Differentials?
And is it worth a smooth grand to upgrade if you are really interested in getting power to the ground?

[edwardb]

Edward can you tell what type of bushings/bearings on in the hub control arm mount points. I am hoping they are modern style and not the old rubber stuff like the old IRS.

I can't say because I don't know anything about nor have ever owned any of the previous IRS components. The 2015 knuckles I just received have a combination of metal and some type of elastomer bushings in the two lower arms. They appear to be in there quite substantially. I don't know if these are intended to be left as is, or replaced with parts provided in the FF IRS kit. I'll find out when the kit arrives. That's all I can say for now.