IRS or Moser 8.8

[Cruzzz]

Well my order is in for a complete kit but with all this time to kill waiting I'm starting to reconsider some choices including my initial selection of the Moser 8.8 solid axle. I have to admit it was mainly based on cost (current deal includes -$100 on Moser and free rear brakes (-$650)). Adding it up without the discounts included its roughly $1300 more for the complete IRS setup from FFR (less brakes). With the brakes for both and the related discounts it is almost a $2,000 difference.

Help me think through this!:D Is IRS worth it?

[Dave Howard]

If you are on a budget, go with the solid axle. The money you save will pay for the Wildwood brake upgrade.

[CraigS]

If you get your Mustang rear suspension from a salvage yard be sure it includes the brakes. They work very well and make the cost differential somewhat less.

[Bob Cowan]

The ride is so much better with IRS that it's worth every penny.

[GoDadGo]

I've had the opportunity to ride in Roadsters with both set ups and liked them both, but went with the solid axle.
The simplistic design of Factory Five's 3-Link set up appealed to me since there is only one drive shaft to deal with.
The solid axle does plant the tires harder than the IRS; however, the IRS is far superior in the ride and handling departments.

Note: ..My old daily driver was a C-4 Corvette and I had to change the U-Joints in the half shafts every 2-3 three years.
............I owned that car from 1995 until July of this year and didn't want to deal with stuff like that again.
............For me form is following function and the simpler the car is, the happier it makes me.

Good Luck Building Your Dream From The Dark Dart Side!

https://youtu.be/NhRHwAbtrt0

[Gumball]

My car has a solid axle and I think the ride is really nice.... even on our crumbling infrastructure here in Illinois. I went with that rear end for a few reasons - 1) when I bought my kit, the 3-link was the performance version and the old T-bird IRS was considered the "comfort" version; 2) simplicity of set-up; and 3) lower cost.

That said, if I were building my car now, I'd go with the new S550 (Mustang) IRS that is offered - for performance, comfort, and period-correct configuration of having IRS.

[rich grsc]

I've had the opportunity to ride in Roadsters with both set ups and liked them both, but went with the solid axle.
The simplistic design of Factory Five's 3-Link set up appealed to me since there is only one drive shaft to deal with.
The solid axle does plant the tires harder than the IRS; however, the IRS is far superior in the ride and handling departments.

Note: ..My old daily driver was a C-4 Corvette and I had to change the U-Joints in the half shafts every 2-3 three years.
............I owned that car from 1995 until July of this year and didn't want to deal with stuff like that again.
............For me form is following function and the simpler the car is, the happier it makes me.

Good Luck Building Your Dream From The Dark Dart Side!

https://youtu.be/NhRHwAbtrt0
There are no u-joints in the IRS suspension.

[edwardb]

Had both. IRS hands down.

[GoDadGo]

There are no u-joints in the IRS suspension.

I know; however, any extra parts that may need to be replaced, including CV-Joints, doesn't make me Hap-Hap-Happy.

[japollon]

I did the 3-link on my 289 FIA for only one reason. I could not get pin drive, 15" wheels with the IRS. Had that been an option, I would have gladly paid the extra money for the IRS. I err'd on the side of the "look" of exterior period correctness. I may live to regret that. Like edwardb, I have owned both rear end versions in a Cobra and while the 3-link is smooth, adequate in the ride and simple, it does not corner or track nearly as well as the IRS in my opinion. I guess it also depends on how you plan to use the car. The 3-link does have some advantages in some situations.

[David Williamson]

I have both IRS is WAY smoother ride, bigger difference than I expected. The IRS coupe is not much harder riding than my '07 BMW 335 with sport suspension. The cobra not close. Very different cars to drive and ride in and the coupe has a longer wheel base so that will influence it too.
BUT all what you want in the car and of course your budget.
David W

[cgundermann]

I have a solid axle and my Pal has IRS. After numerous back surgeries, my next one will be IRS!

Chris

[Cruzzz]

Wow! Thanks for all the experiences! Looks like a solid lean to IRS so far. My use would almost exclusively be for cruising rather than racing.

What is the most cost effective route to purchase all I would need for the IRS if I went that direction? It looks like $4k plus $699 for rear mustang brakes from FFR.

Are front and rear sway bars needed?

[Bob Cowan]

Wow! Thanks for all the experiences! Looks like a solid lean to IRS so far. My use would almost exclusively be for cruising rather than racing.

What is the most cost effective route to purchase all I would need for the IRS if I went that direction? It looks like $4k plus $699 for rear mustang brakes from FFR.

Are front and rear sway bars needed?

No, they are not. Anti-sway bars are used to fine tune the suspension for perfect handling. I used to disconnect mine for street use, and only used them on the track. And, too big of a bar on the rear will sort of turn it into a solid axle.

[CraigS]

I don't get where your numbers are from. FFR lists the IRS option as $2499. Ebay has quite a few salvage IRS units, many W/BRAKES for well under $1000.

[Cruzzz]

$2499 is only for the suspension. It doesn’t include the center section, spindles, and hubs for an additional $1499.

[JohnK]

Give Forte's a call... you'll save a couple hundred bucks on the center section and hub/knuckles.

[edwardb]

$2499 is only for the suspension. It doesn’t include the center section, spindles, and hubs for an additional $1499.

Right. But solid axle isn't free. So there's some offset. Anywhere from $2000 or so for the Moser setup on down to salvage, re-build, etc. And as CraigS pointed out, there are deals out there for the IRS components. Will also be salvage, but way newer than 8.8 solid axles from salvage. No question IRS is going to be a cost adder, but not $4K

[Cruzzz]

I think you misunderstood my previous posts. It is 4K total from FFR with a difference, when compared to the Moser setup, of $1,300. I appreciate the thoughts on going the salvage route but I’m hoping to go all new with this build after working through all the rust on my ‘65 mustang.

Thanks

[edwardb]

I think you misunderstood my previous posts. It is 4K total from FFR with a difference, when compared to the Moser setup, of $1,300. I appreciate the thoughts on going the salvage route but I’m hoping to go all new with this build after working through all the rust on my ‘65 mustang.

Thanks

Don't quite get the math. But doesn't matter and I'm with you on the salvage part. Totally understand budget and we all do what we have to do. If you can figure out how to do IRS you won't regret it. Having had both, as I said, it's a pretty significant improvement and adds considerably to the car's enjoyment. But a properly setup 3-link works very well also. Good luck.

[David Hodgkins]

Cruzzz,

I'm surprised edwardb didn't push you more toward "salvage" IRS. There are some places that have practically new IRS sections that are "zero miles take-off" from upgraded cars. Is that right edwardb? I thought your 20th anniversary has that? Came with brakes too? That's practically brand new and remember, it ain't no 53 year-old rustang!! I found the link:
IRS pallet from edwardb's 20th anniversay build thread (https://thefactoryfiveforum.com/showthread.php?18591-EdwardBs-Mk4-8674-20th-Anniversary-Build&p=209141&viewfull=1#post209141)

Anyway, I am also firmly in the IRS camp for a new MKIV build. I'm also with japollon that it is a real bummer you can't get the pin drive setup with the new IRS. Performance-wise it's a step backward (Longer half-shafts are better geometrically) but IMO you just can't beat that old school look!

Any new build I do will have the IRS option.

:)

[GoDadGo]

The solid axle does plant the tires harder than the IRS; however, the IRS is far superior in the ride and handling departments.


Go For The I.R.S. Unless You Suffer From A Special Kind Of Stupid That We Drag Racers Seem To Have!

This was my primary reason for NOT going with the I.R.S.

[edwardb]

Cruzzz,

I'm surprised edwardb didn't push you more toward "salvage" IRS. There are some places that have practically new IRS sections that are "zero miles take-off" from upgraded cars. Is that right edwardb? I thought your 20th anniversary has that? Came with brakes too? That's practically brand new and remember, it ain't no 53 year-old rustang!! I found the link:
IRS pallet from edwardb's 20th anniversay build thread (https://thefactoryfiveforum.com/showthread.php?18591-EdwardBs-Mk4-8674-20th-Anniversary-Build&p=209141&viewfull=1#post209141)

Anyway, I am also firmly in the IRS camp for a new MKIV build. I'm also with japollon that it is a real bummer you can't get the pin drive setup with the new IRS. Performance-wise it's a step backward (Longer half-shafts are better geometrically) but IMO you just can't beat that old school look!

Any new build I do will have the IRS option.

:)

Hey David. Good memory. Yes, I did use a "zero take-out" IRS pallet for my 20th Anniversary build. That was early in the game and Ford Performance didn't have new parts available yet. So going salvage was my only choice. I wasn't too excited about it because I really wanted new. But what I got supposedly wasn't driven any more than onto the truck at the factory and back off wherever it was taken apart. It was a decent deal, but not much cheaper than what the new stuff eventually was available for. My pallet didn't have brakes, but I didn't need them since the Anniversary Roadster came with Wilwood brakes. I haven't looked a lot recently, but when I have didn't see any zero take-outs available through the various channels. But lots of salvage options now three years later and there are enough out there that savings are possible. Many with low miles and these things are very robust, so with the right history and source, wouldn't hesitate. Was willing to do salvage for my Coupe build, but was specifically looking for a 3.73 Torsen and didn't see what I was looking for. So ended up going new. After having two solid axle Roadsters, and now the 20th Anniversary IRS Roadster, I'm a huge convert so say that whenever the question comes up. Everybody that rides it in is impressed with how it rides. For a typical build budget, it's a relatively small percentage upgrade that has a big upside. But I also realize budget concerns are real.

[Avalanche325]

In the old Thunderbird IRS days, 3-link was the way to go for anything besides comfort (it is a little bit more comfortable, but not huge to me. I just spent a full day in one including autocross). The 3 link out performed the IRS and is much more dependable. I went 3-link Moser.

Now with the new Mustang IRS, I have yet to hear anything but praise for it. I would go IRS if I were building now. I also would not build one without doing Wilwoods.

Everything should always include "if you can afford it". If you can, by the time the car is on the road, the price difference won't be a concern. If you can afford one OR the other, I would take Wilwoods over IRS.

[Fixit]

I found a rotor to rotor, 1000 mile "take-out" IRS from an outfit in Iowa, Midway Mustang (https://midwaymustang.com/) for less than a G-note. Tough part was truck freight was nearly 1/4 the cost of the setup!
(and I mean rotor to rotor - cradle, knuckles, center section, shocks/springs, and complete brakes.)

[SSNK4US]

You guys are killing me!! Lol ;)

Kurt

[caesarmascetti]

hey guys a little off topic, but does anyone know if the new IRS can be retrofitted to a MKiV with the TBird IRS relatively easily?

[edwardb]

hey guys a little off topic, but does anyone know if the new IRS can be retrofitted to a MKiV with the TBird IRS relatively easily?

Define "relatively easily." :p Short answer, no. It's significantly different.

[David Hodgkins]

hey guys a little off topic, but does anyone know if the new IRS can be retrofitted to a MKiV with the TBird IRS relatively easily?

Do you have a MKIV with a t-bird IRS? Is yours configured for pin drive?

:)

[caesarmascetti]

Do you have a MKIV with a t-bird IRS? Is yours configured for pin drive?

:)


nope not pin drive, it is a MKIV with the old IRS, has Wilwood rear brakes 5 bolts

[caesarmascetti]

Define "relatively easily." :p Short answer, no. It's significantly different.

ah well nothing is easy

[CraigS]

One more thought. The salvage 315 ratio IRS are even cheaper since almost no one wants them. But that gear is near perfect w/ my torquey 408.

[Cruzzz]

Thanks for all the insight! I updated my order with the complete IRS setup today from FF. In addition to the comments on handling and ride comfort I appreciate the idea that the difference in cost is a small fraction of the overall build.

[Bob Cowan]

Excellent decision! In the end, you won't be sorry. :)