2015 Mustang IRS Components. So it begins.

[edwardb]

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.

I think this is pretty well known and established information. There are a few builds out there with 4-speed toploader transmissions, same as the originals. But the most common manual transmissions for these builds are T-5-s (with several variants) and TKO500/600. All are 5 speed. All fourth is 1:1. All fifth gears are an overdrive. Different models have different ratios. Some in the .80's, some in the .60's. I know that modern DD's are designed to cruise at very low RPM, some as low as the 1200 you mention. Most performance engines, however, are cam'd to get their torque at a higher RPM, and will not be happy at that speed. Very generally, most need to be kept at 1,900 - 2,000 or higher in some cases. The best O/D and final drive ratios are dependent on a number of factors, and vary a lot from build to build.

[edwardb]

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?

I believe your information is correct. Only the 3.73 comes from the factory with the Torsen option. But the assembly can be bolted into one of the other ratios. There is a method to setting up the internals in these diffs, involved shims, checking and setting lash, etc. So unless you know what you're doing, probably should be done by a pro.

The Ford Traction Lok is a clutch style system where the Torsen is a gear style system. No question the Torsen is technically a better system. Do you need to spend the extra money and would you notice the difference? For normal street cruising, probably not. For track use, and apparently especially Auto-X, it is a better setup. I've had regular Traction Lok on my first two builds, and for my purposes and use, it's fine. Not planning to change out the Traction Lok in the new build with the 2015 setup either. I'll spend the money elsewhere. More discussion here FWIW:

http://www.ffcars.com/forums/21-ffr-...-trac-loc.html

http://www.ffcars.com/forums/17-fact...slip-diff.html

http://www.ffcars.com/forums/17-fact...-trac-lok.html

http://www.ffcars.com/forums/66-2006...en-vs-lsd.html

[Jazzman]

I just called MPS Salvage to order the same setup that you bought, and was told they don't have any left. Everything that they had was just purchased by . . . Factory Five!!! I don't know how many IRS "take off's" that is, but MPS doesn't have any more at the moment. They said they often get them, so call them back in a couple of weeks. Or maybe Factory Five is reselling them. Who knows. Since I was just stockpiling parts anyway, that isn't a big deal to me. I'll call in a couple of weeks . . . or three, maybe four.

[rickscobra]

Happy to report that my kit will have all the 20Th Anniversary items short of the badging, silver chassis powder coating, and white powder coated engine compartment panels. This was most welcomed news. Kit should be ready for pick up on 19 September.

[edwardb]

I just called MPS Salvage to order the same setup that you bought, and was told they don't have any left. Everything that they had was just purchased by . . . Factory Five!!! I don't know how many IRS "take off's" that is, but MPS doesn't have any more at the moment. They said they often get them, so call them back in a couple of weeks. Or maybe Factory Five is reselling them. Who knows. Since I was just stockpiling parts anyway, that isn't a big deal to me. I'll call in a couple of weeks . . . or three, maybe four.

Interesting. They still have a number of active listings on eBay. Those were sold too? There is another seller on eBay that is listing them as well. Will be watching to see how this all plays out when the first 2015 Mustang IRS kits start deliveries to builders in the next few weeks.

[edwardb]

I just called MPS Salvage to order the same setup that you bought, and was told they don't have any left. Everything that they had was just purchased by . . . Factory Five!!! I don't know how many IRS "take off's" that is, but MPS doesn't have any more at the moment. They said they often get them, so call them back in a couple of weeks. Or maybe Factory Five is reselling them. Who knows. Since I was just stockpiling parts anyway, that isn't a big deal to me. I'll call in a couple of weeks . . . or three, maybe four.

This morning I received an email from Factory Five offering a 2015 Mustang center section and knuckles/hubs for my 20th Anniversary Roadster kit order. The email said they were zero miles Mustang take-off parts, so clearly these same ones. I won't post the price offered, but it was on par with what I paid directly. I obviously don't know their plan for offering these assemblies to customers needing the pieces. The supply is limited. Maybe others are hearing from them as well?

Also got a message today that my kit is going into production and to call for final details. Looks like my early August date is really going to happen.

[Georg]

Me as well got the mail from FF and I added this new option to my 20th anniversary kit order. Will safe a lot of research and trouble I guess - seems to be a great deal...

My completion date was scheduled for end of August. So looking forward to follow your build Paul, guess you will be twice as fast as me since this is my first build. All the best!

Georg

[rickscobra]

I am a happy camper as well. When I called FFR and asked about securing one of the MPS IRS assemblies, they added it to my order One less thing to have to chase down. Now I am looking at tires for the new 18inch wheels. This is going to be a fun adventure. Delivery date is 19 September, but I may well wait till 24 September to pick it up. Will make a great birthday present.

[edwardb]

Yesterday I finished prepping the 2015 Mustang IRS center section for my upcoming build. I drained the fluid by tipping it sideways and out the axle holes. Probably perfectly good fluid, but I'll feel better giving it a fresh start including friction modifier as specified once it's installed. Plugged the open axle holes with clean shop rags, and cleaned everything up. The iron case just took a little wire brushing with various size wheels in a hand drill and then Scotch-Brite. Peeled the stickers off the rear cover (after taking several pictures) and cleaned it up as well. I sprayed clear Dupli-Color engine enamel on the back cover. Then brushed black POR-15 engine enamel on the iron case after a thorough cleaning with POR-15 degreaser and metal prep. I was careful to not get anything very wet and especially around the front seal. My shop crane was handy for this project. That thing is not light and kind of clumsy to move around. Didn't take any pics yet, but also cleaned up the knuckles and hubs. I'm going to put some clear on the knuckles too, but not until I get the kit and instructions. Best I can tell, as mentioned before, the upper arm gets trimmed back a bit.

This was a relatively lightweight clean-up job given the age and basically zero time on the road. But let's just say I have a new found appreciation for you guys that have the patience to harvest real live donor parts with years of rust and grime to clean up. I've avoided much donor work to date, and probably will keep it that way.

So now I just need a chassis to put this stuff in! We're off to Factory Five next week, with our pickup date of Wed, Aug 5, now confirmed.

Cleaned and ready for finish:


All done. Compare this to the orange rusty look earlier in the thread. Nice improvement.


Clean and shiny rear cover. I'll be interested to see how that vent is handled. I don't remember seeing how it was plumbed when I saw the new suspension at the Open House.

[BobCarter]

Nice cleanup. Looks very good with the paint and clearcoat. I got a couple pictures today of my 20th and i think your kit was also visible. Ill send you the pic when i figure out how to do it. I'm not picking mine up at FFR so I have to wait for Stewarts delivery date.
looking forward to sharing our build activities with each other. Safe travels!
PS I learned that my quick response to Dave Smith's 20th Anniversary announcement put me right behind the FFR donor to the Ohio club. They will receive serial number 1, that put me in with serial number 2. I bet you will be number 3. Very cool.

[edwardb]

Nice cleanup. Looks very good with the paint and clearcoat. I got a couple pictures today of my 20th and i think your kit was also visible. Ill send you the pic when i figure out how to do it. I'm not picking mine up at FFR so I have to wait for Stewarts delivery date.
looking forward to sharing our build activities with each other. Safe travels!
PS I learned that my quick response to Dave Smith's 20th Anniversary announcement put me right behind the FFR donor to the Ohio club. They will receive serial number 1, that put me in with serial number 2. I bet you will be number 3. Very cool.

Cool! I called right after the details were posted on-line to order mine, and they said someone was already on the phone ordering one. I'll bet that was you at number 2, and have wondered if I would be number 3. Would love to see whatever pics you have. PM sent.

[BobCarter]

Cool! I called right after the details were posted on-line to order mine, and they said someone was already on the phone ordering one. I'll bet that was you at number 2, and have wondered if I would be number 3. Would love to see whatever pics you have. PM sent.

3 pics sent

[CraigS]

Here is my experience w/ the two types of lim slips. In my FFR I had the standard LOK for 3-4 years but decided to upgrade to a TrueTrac (very similar to a Torsen) for autocrosses. Very little difference at the autocrosses but one thing I did definitely notice was more driveline slop. Posted here and found that is a characteristic of those units. Recently my wife traded in her 2010 Mustang GT stick w/ LOK on a 2015 GT stick w/ the Performance Package which includes the 373 Torsen. The first weekend after she had been driving it we go for a ride because she has questions. She had noticed the driveline slop although it is less than in my FFR due to the rubber in the diff mounts and control arms. She also noticed that, when pulling out from a stop and making a 90 degree turn, it makes some noise. The noise she hears is the inside tire spinning slightly as the Torsen locks up. It is more obvious w/ more throttle or w/ gravel on the road. My thinking is that the standard Ford LOK is much nicer on the street w/ nearly no downside unless you drive extremely hard.

[RRussellTx]

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.

CraigS,

I'm concerned about the bushings that that come with the 2015 IRS kit to mount the differential in the chassis. They are not rubber and seem like some kind of poly but they are very light and I think very soft for what they are going to be used for. I see from your posts that you have some experience in this area.

What are your thoughts on the expected lifespan of this part and how it would perform under a high load in a light car?
I REALLY don't want to pull the differential after a year or two of service...

It's probably fine for my use but I would be mad at myself if I did not do some due diligence before I installed the unit?

Here is a pic of the part where I am showing off my manly grip and compressing it a bit to show how soft it is.


Thoughts or opinions from anyone would be appreciated!

[edwardb]

Well you know from our brief discussion in your build thread that my opinion is these will be OK. But several things occur to me. I don't think the experience with the previous IRS mounting is completely applicable to the new 2015 Mustang setup. The previous design has a vertical flange mount along the center of the rear cover, and two vertical bushing mounts on each side of the nose at the front near the pinion flange. This design, which has been very successful BTW, would seem not as capable to resist twisting forces as the 2015 Mustang setup which has four wide horizontal mounting locations. So I'm not sure how much experience with the old design applies to this one. The other point is these four mounting points are very solidly wedged into the chassis. Trust me when you try to install, you will find out just how tightly it's wedged in there. This too would really resist motion in any direction. More than just the bolts pressing against the sleeves in those bushings. Those are some of the reasons I think it's OK. But I understand your concern and I don't want to take it out again either.

The other thought would be call Factory Five. Try to get feedback from one of the design guys, not just the tech support guys answering the phone. Of course they're not going to tell you they designed and sold us a kit with a defective design. But it may be useful to find out just how much this new setup has been actually tested, and what their experience has been from that testing. Maybe that would give you some confidence. Or not. During the FF Open House, when Dave was unveiling the 20th Anniversary Edition Roadster, he spoke at some length about the new IRS. It's been under development for a while, and he described quite a bit of track testing, beating previous best times, etc. Maybe there's something to be learned from that. Just a thought. I too will be interested in what others think.

I'm not a chemist, but I'm also pretty sure those are poly. For those reading this that don't know, the pictured bushing is one of two for each of the four mounting points. They are pressed into steel tubing welded to the chassis, and have a steel bushing through the center for the mounting bolts. M14 bolts (.55 inches) in the back, M16 (.63 inches) in the front.

[CraigS]

Googling '2015 mustang rear wheel hop' I found this;
https://www.youtube.com/watch?v=dA0kzu4Ukzk
Steeda is stiffening the subrame to body mounts and leaving the diff to subframe mounts alone. You can see the bolt head of the diff mount move quite a bit and also notice that the stock bushings are much larger than the one you picture and have voids in them. My "guess" is yours will be fine.

[RRussellTx]

Thanks guys. I really appreciate your perspective!
I'm going to do some more research this weekend so let me know if anyone else has any thoughts.
Since this IRS is so new I really want to consider everything carefully while I'm at this stage of the build.

[RRussellTx]

I called FFR and confirmed that the Diff bushings are Energy Suspension Poly bushings. I got my hands on a similar set of Energy Suspension bushings to compare the hardness. The ones I have for comparison are the same material as the ones in the kit but they seem a lot harder (more like I am used to). But they had a much smaller ID for the bolt to go through so the bushing was much thicker and therefore firmer. After looking at both and talking to several knowledgable people, I am convinced that the bushings are just fine.

I also was able to get my differential mounted this weekend and I don't think it would be possible with bushings that are very much harder. I also followed some steps that made it a little easier so I thought I would share those here in this thread.

First, don't install the steel tube spacers all the way in the bushing before you start. You can get them started in the bushing on the outside of the differential but just press them in about an inch.
Then you can position the differential in place and start the threaded bolts in the rear cover first.




Make sure you get a good start on the threads but don't tighten any of them down until you get all 4 of them started. Once you get them all started then you can just tighten them a little at at time depending on which one needs to come in first until they are all tight.



One other thing that helped when I drilled out the differential was to grind down the tip of a 5/8's bit to a small enough diameter to fit into the existing hole. It might have been fine anyway but with this it was super easy was drilled out in just a few seconds.



Sorry about being concerned about the bushings but I'm 100% convinced that they are the best option now. Good luck installing yours!

[edwardb]

Excellent follow-up and suggestions! Great information.

[ThickCobra]

Any thoughts as to whether adding chassis lube to the bushings would help? And, should I as a rule use chassis lube on poly bushings elsewhere?

[edwardb]

Any thoughts as to whether adding chassis lube to the bushings would help? And, should I as a rule use chassis lube on poly bushings elsewhere?

Yes, use your chassis lube of choice anywhere there's a Zerk fitting. I use Red Line CV-2 (O'Reilly's) but don't think there's anything magical about the brand to be honest. A little on the center section bushings during installation wouldn't hurt anything. But I'm not sure how much it would help. They're just mechanically very tight.

[CraigS]

I use synthetic grease where ever I feel the need. Oil based grease can attach some types of plastic. Since I am not always sure what exact compound I might be dealing with, I figure synthetic is safe for everything.

[toadster]

All done. Compare this to the orange rusty look earlier in the thread. Nice improvement.


Clean and shiny rear cover. I'll be interested to see how that vent is handled. I don't remember seeing how it was plumbed when I saw the new suspension at the Open House.

Paul - I love going through your build threads, I hope my IRS looks 1/2 as nice as yours... it's time to get workin on my end now!

curious as to which grit Scotch Brite you used - that diff cover SHINES!

3-grades pack
Sc85osz.jpg

[Aircontroller]

Interesting vid about the Torsen below. Posting for future reference.

The guy narrating the vid made an interesting point that I have to review again regarding calibrating the speedometer for the type of transmission.

https://youtu.be/EVXDor-2IxQ

[Aircontroller]

I had just PM’ed Paul the same compliment!

Paul - I love going through your build threads, I hope my IRS looks 1/2 as nice as yours... it's time to get workin on my end now!

curious as to which grit Scotch Brite you used - that diff cover SHINES!

3-grades pack
Sc85osz.jpg

[edwardb]

Thanks guys. Brings back memories of rehabbing that diff for my 20th Anniversary build. Ford Performance wasn't selling the separate pieces yet at that time, so a donor was the only choice. Even though I got lucky and scored a zero mile takeout, still was rusty and crummy right from the start. For the Scotch Brite, don't remember specifically. They were green and from Home Depot, if that helps. Don't think it's particularly critical. Whatever works. For the comments in the video about calibrating your speedometer, not an issue if you're using the common GPS gauges from Speedhut. They'll be right from the start no matter what. Autometer requires a calibration step as I recall. Over a measured distance. But pretty straightforward.

[Aircontroller]

Hey toadster, any chance you can post what worked for you to get the rust out? I’m mighty curious.....Thank you in advance!

Paul - I love going through your build threads, I hope my IRS looks 1/2 as nice as yours... it's time to get workin on my end now!

curious as to which grit Scotch Brite you used - that diff cover SHINES!

3-grades pack
Sc85osz.jpg

[toadster]

Hey toadster, any chance you can post what worked for you to get the rust out? I’m mighty curious.....Thank you in advance!

I've got a few more hours to go on mine... it was a newer unit from Mike Forte
59943182427__D1D8F339-EC0A-4838-B2A1-6A6542A64543.JPG

I moved the unit outside for a few days when I had the garage epoxied, and I thought I had it covered well, but it rained one night... ugh, it turned orange, I grabbed a green scotch brite and quickly realized, it wasn't going to do much other than scuff... Its meant for polishing, not for stripping...

so I took a wire wheel and did a decent job for about 10 minutes... although, I'll probably switch to a corded drill or my dremel to finish, otherwise I'll be killing my rechargeable batteries...

you can see pretty easily what was initially hit with the wheel
IMG_9521.JPG

the aluminum side shines up nicely, but you need to be careful how much you can cut into the face of the metal with the harder metal wheel
IMG_9522.JPG

so I'll probably use the dremel with some stripping wheels, and buffing wheels to soften the blow... i'll use POR15 on the case, so not super concerned about the finish, but the aluminum I'll hopefully shine up nicely!

60 Pcs brass steel wire polishing brush Wire Brush Wheel Cup set 1/8" (3mm) Shank for Dremel Rotary Tools Polishing Tools Accessories
61s9qTwtr5L.jpg


40 Pack 1 inch Abrasive Wheel Buffing Polishing Wheel Set For Dremel Rotary Tool
618mDNBrbhL._SL1000_.jpg

then I'll use the scotchbrite to finish