Opinions wanted on IRS rear end parts

[Jammer369]

After what has seemed like an eternity (12 years since I retired from the USAF) in wanting to build a roadster I am finally in the homestretch with buy in from my better half and starting to finalize the decisions that need to be made. I am planning on ordering this fall. Up to this point I have narrowed the build specs as follows:

MkIV full kit
Coyote Gen 3 w/TKX. (Forte has a nice package for this)
IRS w/3.55
Hydraulic clutch
Flip Front (luckily I live in the same area as Jazzman. He has been more than generous with his time.)
Leather dash
Custom Speedhut gauges
18" Bronze Forged wheels (FFR 25th Anniversary)
Gas-n touring sidepipes
Wilwoods all around
Wilwood electric parking brake
Breeze Rollbars (both sides)
Breeze Front battery box
Power Steering
AC (I live in Phoenix)
Premium Soft Top
Wind wings
Visors


TDB:
Seats
Type of sound and heat insulation
PTFE braided or hard fuel and brake lines
Tires


So one thing I have had a hard time pondering and the only thing on the car I would consider purchasing as used is the rear end IRS components. FFR sells the center section, hubs and spindles for $1499. Forte sells it for $1240.

I have alerts setup on eBay for the rear assembly that include pretty much the entire IRS section with the center section, axles, hubs, brakes. I have done a bunch of research on the issue of Torsen-Lok vs Traction-lok. I think I would prefer the Torsen if available but I rarely see them w/3.55 used and it seems impossible to order an iron loaded diff carrier with 3.55 and the torsen-lok from ford parts. Ford started offering the Torsen center w/3.55 on Mustang GT's in 2018 if you order the performance package.

I found one that is at the parts farm in GA now. It is out of a 2019 GT w/ecoboost (16,000 miles on it) and has the Cast Iron 3.55 w/Torsen. it is listed as $1099 + freight. It is the first one I have seen on almost the 9 months I have been watching. I have a couple of questions.

1. Does the Torsen make as much of a difference over the clutch type in the normal gt center section?
2. Would you rather have a used Torsen or new regular center section?

I don't mind starting to accumulate the parts now and getting them cleaned up and selling the items I won't use from the IRS section.

Advice appreciated.

Thanks,
Troy

[chmhasy]

Try www.car-parts.com for local auto recyclers

in the search area select
Axle Assy Rear( w housing) or carrier or differential

You may need to play with the selection

[edwardb]

I had a 3.55 traction lock in my #8674 Roadster build with IRS. Was from salvage, but a zero miles take-out. So new except for the rust. I have a 3.73 Torsen in my Gen 3 Coupe with IRS. Bought new when Ford Performance was still selling them. Much more expensive than the one you're asking about. :rolleyes: As you said, Ford started offering the 3.55 Torsen in 2018. But not offered for sale by Ford Performance. I wouldn't hesitate to use the one you mention if you really want Torsen. They're extremely robust and short of outright abuse should still be rock solid in your build. Both builds have build threads linked in my sig line below with more details and pictures if you're interested. My Roadster was one of the very first builds with the new 2015+ IRS. A lot of people were interested in it so posted lots of pictures and such.

Drove the Roadster with traction lock over 5K miles. I'm at around 2.5K on the Coupe with Torsen. I'm basically 100% street cruising and admittedly pretty conservative. But I feel like the Torsen is more planted. With any wheel spin, it stays straight where the Roadster would wiggle a little. Cornering feels solid. I used it because I wanted to try Torsen plus the 3.73 ratio I felt was most compatible with the T-56 trans in that build. I like it and would use it again. The only negative I'd cite is the Torsen makes a bit of noise. You can hear the gears loading and unloading a bit when you get in and out of the throttle. It's not bad and not a big deal. Just hear it compared to the traction lock. May not be as noticeable in a Roadster with the trunk and rear cockpit wall compared to the open hatch area on the Coupe. But the Mustang guys note the same thing.

Good luck with your build.

[Jammer369]

I had a 3.55 traction lock in my #8674 Roadster build with IRS. Was from salvage, but a zero miles take-out. So new except for the rust. I have a 3.73 Torsen in my Gen 3 Coupe with IRS. Bought new when Ford Performance was still selling them. Much more expensive than the one you're asking about. :rolleyes: As you said, Ford started offering the 3.55 Torsen in 2018. But not offered for sale by Ford Performance. I wouldn't hesitate to use the one you mention if you really want Torsen. They're extremely robust and short of outright abuse should still be rock solid in your build. Both builds have build threads linked in my sig line below with more details and pictures if you're interested. My Roadster was one of the very first builds with the new 2015+ IRS. A lot of people were interested in it so posted lots of pictures and such.

Drove the Roadster with traction lock over 5K miles. I'm at around 2.5K on the Coupe with Torsen. I'm basically 100% street cruising and admittedly pretty conservative. But I feel like the Torsen is more planted. With any wheel spin, it stays straight where the Roadster would wiggle a little. Cornering feels solid. I used it because I wanted to try Torsen plus the 3.77 ratio I felt was most compatible with the T-56 trans in that build. I like it and would use it again. The only negative I'd cite is the Torsen makes a bit of noise. You can hear the gears loading and unloading a bit when you get in and out of the throttle. It's not bad and not a big deal. Just hear it compared to the traction lock. May not be as noticeable in a Roadster with the trunk and rear cockpit wall compared to the open hatch area on the Coupe. But the Mustang guys note the same thing.

Good luck with your build.

Thanks Paul! I have read over your build thread of the roadster so many times I have lost count. Your build threads have been a great resource for many.

Your opinion and experience with both versions confirms my thoughts about wanting the Torsen. When I get on the throttle I really want the back end to be as stable as possible. I really think the gear noise won't bother me. I also think the price isn't too bad compared to what I would have to pay for a new setup or zero time pull. I sent a message to the the parts farm asking about the shipping costs. We will see what they say. I read an article recently about the different center sections Ford has used in the Mustang GT's in the past few years. They said the same thing about their robustness. The author of the article said he had opened quite a few of the Torsen center sections up and they had all still appeared new with no wear indications.

Thanks again for the input!!

[Jammer369]

Try www.car-parts.com for local auto recyclers

in the search area select
Axle Assy Rear( w housing) or carrier or differential

You may need to play with the selection


Thanks for the tips to search for other sources!

[Jammer369]

I heard back from thepartsfarm.com this morning. Shipping is $300 via truck freight to Phoenix. So all in for the Center section, hubs and spindles would be $1400. Not sure if there would be a market for anyone who would want the rest of the parts from the rear end clip assembly but if so, that would reduce the costs even further.

[BradCraig]

I heard back from thepartsfarm.com this morning. Shipping is $300 via truck freight to Phoenix. So all in for the Center section, hubs and spindles would be $1400. Not sure if there would be a market for anyone who would want the rest of the parts from the rear end clip assembly but if so, that would reduce the costs even further.

There really isn’t a market for the left over parts unfortunately. Prices have def gone up, I paid $600 for mine from parts farm plus shipping!

[edwardb]

There really isn’t a market for the left over parts unfortunately. Prices have def gone up, I paid $600 for mine from parts farm plus shipping!

X2 on leftover parts from a full IRS pallet. I was able to sell a few on eBay. Nothing on local Craiglist. Net price after eBay fees, packing stuff up, etc. (even with buyer paying shipping) wasn't worth my time. People are buying aftermarket parts. But not OE stuff, like control arms, axles, etc.

$600 for a Torsen setup like mentioned here? Haven't seen any that cheap. If you did, good find. Regular traction lock and especially the unchangeable 3.15 units are much cheaper.

[Jammer369]

X2 on leftover parts from a full IRS pallet. I was able to sell a few on eBay. Nothing on local Craiglist. Net price after eBay fees, packing stuff up, etc. (even with buyer paying shipping) wasn't worth my time. People are buying aftermarket parts. But not OE stuff, like control arms, axles, etc.

$600 for a Torsen setup like mentioned here? Haven't seen any that cheap. If you did, good find. Regular traction lock and especially the unchangeable 3.15 units are much cheaper.

I am not really counting on selling any of the leftover parts to be able to justify the price of the pallet kit, it was just a thought. I might try to pass along the brakes and rotors if I find someone that wants to pay the shipping.

I think I will go ahead and take advantage of the find when they open up on Monday.

Thanks for the help!

[CraigS]

Why not use the brakes? I did and they work great. Since the park brake is inside the rotor like most OEMs, there is no need for a separate park brake caliper.

[BradCraig]

X2 on leftover parts from a full IRS pallet. I was able to sell a few on eBay. Nothing on local Craiglist. Net price after eBay fees, packing stuff up, etc. (even with buyer paying shipping) wasn't worth my time. People are buying aftermarket parts. But not OE stuff, like control arms, axles, etc.

$600 for a Torsen setup like mentioned here? Haven't seen any that cheap. If you did, good find. Regular traction lock and especially the unchangeable 3.15 units are much cheaper.

No, standard 3.55 for $600 but even those are going for 8-900 now.

[chmhasy]

I just looked up using car-parts.com

year 2015
Ford Mustang
Carrier (see also Differential)
Southwest
sort by distance
85001

Next page selected GT, 3.55 ratio

Return results of over 2 pages of carrier assembly for $300 to $800 all different years from 2015 to 2020

I don't know what that includes

[BradCraig]

I just looked up using car-parts.com

year 2015
Ford Mustang
Carrier (see also Differential)
Southwest
sort by distance
85001

Next page selected GT, 3.55 ratio

Return results of over 2 pages of carrier assembly for $300 to $800 all different years from 2015 to 2020

I don't know what that includes

The typical rear end drop out assembly includes the whole rear end just dropped out of the car. The only parts you will use are the center section, spindles, and brakes (if not doing Wilwood). Sometimes the brakes are stripped off so pay attention to that. If they say "carrier" they may just mean center section. Below is an example:

https://thepartsfarm.com/products/2018-2021-ford-mustang-gt-ecoboost-carrier-assembly-3-55-ratio?_pos=18&_sid=3492c33b4&_ss=r

[Jammer369]

I just looked up using car-parts.com

year 2015
Ford Mustang
Carrier (see also Differential)
Southwest
sort by distance
85001

Next page selected GT, 3.55 ratio

Return results of over 2 pages of carrier assembly for $300 to $800 all different years from 2015 to 2020

I don't know what that includes

Thanks for helping me out on the search!

I just checked on those listings and they are all just the Center Section. A few of them looked like duplicate entries by different parts yard so not sure how that worked out. When I searched that parts yard for the listing, it said it couldn't find it. I might be missing something but I can't find a link in the listings from Car-parts.com that takes you directly to the part on the individual yards website. Instead I had to search on the yards website directly. Maybe I am missing something.

i am looking for the entire IRS drop out so I can get the Center Section, hubs and spindles.

[Jammer369]

The typical rear end drop out assembly includes the whole rear end just dropped out of the car. The only parts you will use are the center section, spindles, and brakes (if not doing Wilwood). Sometimes the brakes are stripped off so pay attention to that. If they say "carrier" they may just mean center section. Below is an example:

https://thepartsfarm.com/products/2018-2021-ford-mustang-gt-ecoboost-carrier-assembly-3-55-ratio?_pos=18&_sid=3492c33b4&_ss=r

That's exactly what I am looking for. In fact, your example link is the exact drop I am looking to order from them. It looks to be in decent shape. I messaged them on Friday and confirmed it was a cast iron carrier and had the Torsen diff.

[NiceGuyEddie]

As far as budgeting, please consider that some guys have spent close to $1000 to align an IRS car. That's a wod of cash compared to your average $79.99 front-end alignment.

[Jammer369]

As far as budgeting, please consider that some guys have spent close to $1000 to align an IRS car. That's a wod of cash compared to your average $79.99 front-end alignment.

That is a crazy amount to get an alignment. Thanks for the heads up! I am still planning on gong with the IRS but now I have another item to add to the cost spreadsheet.

Troy

[BradCraig]

As far as budgeting, please consider that some guys have spent close to $1000 to align an IRS car. That's a wod of cash compared to your average $79.99 front-end alignment.

$1000? That's insane, looks like the "I don't want to do it" price. I had mine done for under $200.

[Railroad]

$179.00 plus a $20 tip. Someone HAD more money than sense.

[chmhasy]

Troy,
car-parts worked out very well for me when I was building here in CT. I have a pre 2015 MKIV running Lincoln IRS, I was able to get the full assembly spindle to spindle for $250

There are some really good threads on how to do an alignment on the forum.


https://www.youtube.com/watch?v=IxnK1XE6ZAA

[Jammer369]

Troy,
car-parts worked out very well for me when I was building here in CT. I have a pre 2015 MKIV running Lincoln IRS, I was able to get the full assembly spindle to spindle for $250

There are some really good threads on how to do an alignment on the forum.


https://www.youtube.com/watch?v=IxnK1XE6ZAA

That's an awesome deal you scored! I will continue to watch car-parts.

Thanks for the link on the alignment!

Funny true story about a shop alignment gone wrong. I bought a 68 Mustang Coupe at a junkyard in Dallas for $50. It was a mess. Short story is I completely rebuilt it with all new suspension parts and did a rough alignment in my garage. I was just about to drive out to Phoenix to start USAF pilot training and wanted a set of new tires. I asked them to do an alignment since I had never had a shop alignment done. The shop told me they couldn't get it to align because I had done something wrong when I rebuilt the front suspension. I had been driving it for a year that way and it had been fine. On my way out of town after leaving the tire store, I noticed a weird tire whine so I pulled over to the side of the highway to check it out. One of the new front tires had worn practically all the tread off the outside of the tire. I got out my tools out (I was moving so I had my whole roll around toolbox with me). I got under the car and loosened everything up on both sides and had a buddy riding with me walk about 50' in front of the car. He would sight down both sides as I nudge the alignment back to just about where I had it before the tire store jacked it up. I tightened everything up and drove it that way for the next 2 years until I purchased a 90 Mustang GT after graduating pilot training. I sold it to a guy on base who gave it to his daughter as a gift. She totaled it 3 months later. I have always regretted selling it.

i will ask the guys here in Phoenix who they used and take it there when I get the roadster to that point.

Thanks again for the help!!

[chmhasy]

That's an awesome story. 50' alignment

[edwardb]

There has to be a back story for a $1000 rear alignment. Not typical at all. I get that a lot of builders don't want to do their own alignment. And also that IRS will have an upcharge over solid axle. But my opinion is always been if you can build a car you can learn to your own alignment. For a few hundred dollars you can have decent tools to do your own and not pay anyone. Also sometimes able to be borrowed from other builders in your area. Exact tools are used for the rear IRS as the front. Just one less axis to deal with. The now standard 2015+ IRS is relatively easy to adjust compared to the past with nothing having to be disassembled.

[Jammer369]

I pulled the trigger on this IRS assembly. Really excited to see this project finally get started. I talked to the guys at thepartsfarm. Found out that the car this came from was a front end damaged car with not hits or damage to the rear of the car. Can't wait to get it in my shop.

Thanks again for the incite guys!

Paul, your experience with having both a clutch type in the roadster and torsen in the coupe really solidified my decision. Thanks again!

[CobraboyDR]

I had a 3.55 traction lock in my #8674 Roadster build with IRS. Was from salvage, but a zero miles take-out. So new except for the rust. I have a 3.73 Torsen in my Gen 3 Coupe with IRS. Bought new when Ford Performance was still selling them. Much more expensive than the one you're asking about. :rolleyes: As you said, Ford started offering the 3.55 Torsen in 2018. But not offered for sale by Ford Performance. I wouldn't hesitate to use the one you mention if you really want Torsen. They're extremely robust and short of outright abuse should still be rock solid in your build. Both builds have build threads linked in my sig line below with more details and pictures if you're interested. My Roadster was one of the very first builds with the new 2015+ IRS. A lot of people were interested in it so posted lots of pictures and such.

Drove the Roadster with traction lock over 5K miles. I'm at around 2.5K on the Coupe with Torsen. I'm basically 100% street cruising and admittedly pretty conservative. But I feel like the Torsen is more planted. With any wheel spin, it stays straight where the Roadster would wiggle a little. Cornering feels solid. I used it because I wanted to try Torsen plus the 3.73 ratio I felt was most compatible with the T-56 trans in that build. I like it and would use it again. The only negative I'd cite is the Torsen makes a bit of noise. You can hear the gears loading and unloading a bit when you get in and out of the throttle. It's not bad and not a big deal. Just hear it compared to the traction lock. May not be as noticeable in a Roadster with the trunk and rear cockpit wall compared to the open hatch area on the Coupe. But the Mustang guys note the same thing.

Good luck with your build.Would you compare/contrast the 3.55 vs. 3.73 gears, since I understand you've had both??

[edwardb]

Would you compare/contrast the 3.55 vs. 3.73 gears, since I understand you've had both??

Really can't because the two builds were different. The 3.55 IRS diff was on a TKO600 Roadster. The 3.73 IRS diff is on my current T56 Coupe. There's just enough gearing difference between the TKO and T56 that according to the calculators they're nearly the same when set up that way. So I really don't notice much difference. At least 1-4. I do like the 5th road gear on the T56 before going into the full overdrive in 6th like the TKO has in 5th. But that's a different discussion.