sj9ers
New Reader
7/12/20 11:13 a.m.
Hi guys I'm currently build a 67 Mustang that's on a frame jig and everything is basically getting replaced. I was looking at rear end setups for a 3 link/ 4 link etc and there all in the $5K plus range when factoring in the cost of the kit and a finished rear end with gears brakes etc. I've always wanted an IRS and stumbled upon people using the S550 IRS into Datsuns, F100s, and the Factory Five Cobra uses them in their kit cars. It seems like the best rear end setup for the money when I checked the shipping to my door the whole setup would be $1200 for a rear end complete with disc brakes and 3.73 gears. Would only have to fab the cradle and source coilovers and shorten the axles since the track width is 65" compared to a 67 Mustang track of 59.25. I figured I could do the whole swap for 3 or 4k. I was wondering if anyone here has done a swap like this into their cars or seen and other builds that have fabbed a cradle to swap the S550 IRS in. I attached pics of some of the setups I've seen.
I'd still consider the 3 link or a truck arm setup, because by the time you shorten the axles and fabricate new suspension links to narrow the rear, there won't be much cost savings. It sounds like you can buy the suspension, but you will be throwing away everything but the knuckles and the differential.
I don't have anything to add to this, but I'm interested in anything you can find out. I've got a '67 Mustang that I've got to figure out the suspension for.
I've kept an eye on local junkyards to see if any of those Mustangs come in.
Ok, I'll say it. Flares!!!!
Done.
If your intent on a "sleeper". (You'll be spending more on everything to maintain the look.) Just buy the 3 or 4 link that fits.
On second thought, it makes a lot more sense to narrow the subframe, not the links. Narrowing the links would throw any toe and camber curves way out of whack, because shortening everything 3" would make some links proportionately shorter. Do that to a toe link and you get wild toe changes with suspension travel. Not a problem if you make the suspension so stiff that it barely moves, but if you're going to do that, you might as well just keep the leaf springs.
sj9ers
New Reader
7/12/20 2:50 p.m.
Pete. (l33t FS) said:
On second thought, it makes a lot more sense to narrow the subframe, not the links. Narrowing the links would throw any toe and camber curves way out of whack, because shortening everything 3" would make some links proportionately shorter. Do that to a toe link and you get wild toe changes with suspension travel. Not a problem if you make the suspension so stiff that it barely moves, but if you're going to do that, you might as well just keep the leaf springs.
That was my plan. Essentially do what factory five did and bring the suspension mounting points inward without altering the control arm lengths. I've already contacted them and they sell the control arms and shafts separately all for about 1500. The only thing I would need to figure out is making the cradle to mount everything and they already provided some of there suspension pickup points to get me started. Just looking for others who have done the same.
And now I'm thinking about the possibility of going halves on a wrecked copart S550 with someone. I get the engine and trans, they get the running gear.
it might make a 5L swap for my S197 cheaper than a supercharger.
Not much to add from a installation POV. The 2 difficulties from seeing other installs on full frame cars are spring pocket location and shock mounts. Couple I've seen use a set of rear coilovers which eat into the cost savings.
Video of one for an F100 install. https://www.youtube.com/watch?v=7onv7iGxdKk
Just a picture of one solo for a visual.
The rear suspension from a Nissan 240sx is closer to the width you need. The R200 diff default ratio is 4.08:1 but others are available. It's plenty strong and is a common swap in Turbo'd S2k's.
STM317
UltraDork
7/13/20 6:21 a.m.
Have you looked at 03-04 Cobra IRS? They're significantly narrower than the new stuff. I want to say something like 61.5" between the wheel mounting surfaces. I can check when I get home if it would be helpful.
sj9ers
New Reader
7/14/20 2:07 p.m.
In reply to STM317 :
I would use the 03-04 Cobra IRS but they're getting harder to find and by the time you upgrade all teh bushings etc your into it a good chunk of change. I've already talked to Factory Five and their IRS width is 59.25" which is perfect for a 67. My plan is to use their control arms and half shafts and fab my own cradle that will bolt in to the existing leaf spring mounting points to locate everything. I'm doing everything in my CAD program first to get a rough idea if it will fit.
In reply to sj9ers :
Just spit balling ideas here but IIRC S13 240SX rear track width is 57-58" It might be harder to find a full rear subframe that isn't totally hammered and the diff isn't as strong as the 8.8 but the aftermarket is unlimited in the 240SX world.
I have a rough CAD model of C4 Corvette suspension if you want to investigate that route at all.
sj9ers
New Reader
7/16/20 1:19 p.m.
In reply to RacetruckRon :
If you could PM me the file for the C4 suspension that would be great. My current plan is to fab a bolt in/out cradle that attaches to the current leaf spring mounting points. The datsun/240z guys are already swapping this diff into their cars but with custom length axles/uprights.
https://forums.hybridz.org/topic/130954-super-88-irs-diff-swap-kit/
Oh dear god stay away from the C4 suspension. The roll center is way too high because the axles are the upper suspension link. This also means you will have about .5 degree of camber slop due to the endplay inside the differential.
A lot of the reason the C5 was a much better car was that they got rid of that mess, which made sense (sort of) in 1963 when they first started doing it.
Any Updates on the FFR IRS Set Up?? I have most of the Mustang IRS Parts. Originally I was going to buy a copy of the display frame from FFR Racing, But Tony left to work at Barret Jackson, and they wanted to double the price on me. for the same parts. Left me know if you have A CAD drawing made up yet?? I want to just buy the FFR Control arms.
Thanks RW
