Read End for 1979 V8 Marcury Capri for Mk4 Roadster

[Magic Islay Malt]

Hello, I'm on the donor parts quest.
Have an engine and almost have a T5.
Would a Rear End from a 1979 Mercury Capril be suitable for a Mk4 Roadster. Its a bit outside the MY window in the manuals and FFR info.
Wondering if anyone has experience of one.
Thanks in advance.

[rich grsc]

No, that is a 7.5 rear end you need an 8.8 Ford rear end

[TrackDay17]

If you haven't ordered your kit yet I'll pass on what one of the instructors at the build school told us.
His thoughts were it's probably cheaper to find a center section out of a 2015 plus Mustang in a wrecking yard this day in age than a regular rear end.
His reasoning was that almost every car sold today has IRS unless it's a pickup.
Also the Mustang rear end handles even supercharged high horsepower Coyotes so it won't be an issue in our cars.

[Magic Islay Malt]

If you haven't ordered your kit yet I'll pass on what one of the instructors at the build school told us.
His thoughts were it's probably cheaper to find a center section out of a 2015 plus Mustang in a wrecking yard this day in age than a regular rear end.
His reasoning was that almost every car sold today has IRS unless it's a pickup.
Also the Mustang rear end handles even supercharged high horsepower Coyotes so it won't be an issue in our cars.

Thats a really good thought and hard to disagree with.
It turns out the axle I'm considering was on a 1979 Capri, but it may have been changed and is a 8.8, we will be checking cover plates this weekend.
My dilemma becomes, do I pay for IRS or go 3 link and use an old axle being donated to me.
If it turns out not to be an 8.8 - decision made.
Oh, the trials and tribulations of Roadster building - and I haven't even ordered my kit yet !!

[TrackDay17]

Thats a really good thought and hard to disagree with.
It turns out the axle I'm considering was on a 1979 Capri, but it may have been changed and is a 8.8, we will be checking cover plates this weekend.
My dilemma becomes, do I pay for IRS or go 3 link and use an old axle being donated to me.
If it turns out not to be an 8.8 - decision made.
Oh, the trials and tribulations of Roadster building - and I haven't even ordered my kit yet !!

It actually happened when we were discussing building a car on a stricter budget like one of the guys was planning.
The guy was planning on searching for a rear end instead of IRS and our instructor brought it up.
He said if you got a good one you were fine but if it needed upgrades like axles, bearings or anything else it could drive your cost up rather quickly.
As he said just go to Youtube and watch a few videos of guys leaving a cars and coffee event and crashing a Mustang so he said the junkyards probably have a few, lol.

I just bought a new one with my kit but if the budget was tight it definitely wouldn't hurt to put some feelers out at the wrecking yards.

[Stangrob]

It actually happened when we were discussing building a car on a stricter budget like one of the guys was planning.
The guy was planning on searching for a rear end instead of IRS and our instructor brought it up.
He said if you got a good one you were fine but if it needed upgrades like axles, bearings or anything else it could drive your cost up rather quickly.
As he said just go to Youtube and watch a few videos of guys leaving a cars and coffee event and crashing a Mustang so he said the junkyards probably have a few, lol.

I just bought a new one with my kit but if the budget was tight it definitely wouldn't hurt to put some feelers out at the wrecking yards.

Totally agree - when I was looking at going with an IRS for my build I was planning to use a rear from a "donor" car.

A number of guys on Ebay sell the entire rear with axles, brakes and other parts needed for the roadster build. Prices are not too bad especially when I look at how much I ended up paying for my Moser rear. Here's an example:

https://www.ebay.com/itm/267616198600?fits=Submodel%3AGT%7CYear%3A2015%7CMo del%3AMustang&_skw=2015+mustang+gt+irs&itmmeta=01KMNA1T4QD545FHS3NG8NKSM9&hash=item3e4f2b1fc8:g:6JUAAeSw~epptRg9&itmprp=enc%3AAQALAAAA8GfYFPkwiKCW4ZNSs2u11xADYjFJh 4EEkpityMc12miNbVaNdOT5nW0yPDCVh3P%2FGHZZJaH5yNgAm Oy6X08jLbiSqccqxL99UX1PnsIITvjGERS%2FFDk%2B5PQjKQX zM5PbUN0nEo4qy7BHWoIKeTPVr2BxZehNalOrZhOMXfmY8QmXy x0%2BgO7zLtXThQP6tB2Lf2eYumT3rTzO4FyDSZ6%2Fnt3VUFe F3qU6grYT8FkmH64FHv4tJSLSJeG%2FXEiXm0W7PQVoIGTvRf1 rnf4UddHhQlm01d%2FkZ5HdgJ9oCbUgIjCa13Hy0GUyZGHZtys G5n4clQ%3D%3D%7Ctkp%3ABk9SR8Sih6qlZw

Rob

[Jeff Kleiner]

The rear end is one of the places where you can really get "sticker shock" when all is said and done.

To add the IRS option is 2,799 but you still need a center section, the spindles and brakes. If you buy all of those from FFR you'll pay 1,750+699 bringing the total to $5,248.

When I built the Mk5 I did like Rob and bought a 6,000 mile drop out with 3.55 Torsen and brakes for $800. Doing something like that brings the total to $3,599.

https://thefactoryfiveforum.com/attachment.php?attachmentid=227305&d=1774543682

If you go with the Moser live axle option you'll pay 3,435 and need to add brakes for 699 bringing the total to $4,134. Keep in mind though that the Moser requires a 3 link rear which if you do a base kit rather than a Complete is another $1,250. In that case the total comes to $5,384.

Finally you can search out a used 8.8 from a Fox or SN95 Mustang. There is no one size fits all however. Whatever you find you should plan on a complete rebuild with all new bearings, TracLok rebuild and gear change (since most are an anemic 2.73;maybe a 3.08) and a change of axles. This is required to get 5 lugs if you start with a Fox or the get to the proper width if you begin with an SN95. If you're using a Fox, in addition to changing to5 lug you'll want to swap it to discs or with an SN95 you'll need to use caliper relocation brackets along with the aforementioned shorter axle shafts. I've done several and if you figure on somewhere around $500 for a salvaged SN 95 rear by the time all is said and done with shorter axles, relocated calipers, new bearings along with a more suitable ring & pinion and refreshed brakes with new calipers and rotors you'll be right around $2,000 all in (pro-tip buy the complete package from Richard Oben at North Racecars for one stop shopping). This assumes that you do the R&P setup labor otherwise you need to add a couple hundred more.

Hope that helps and happy shopping!

Jeff

227305

[tnt_motorsports]

Jeff makes a great point. I bought an 8.8 out of a Fox Body Mustang off of FB Marketplace. It was about $300 and I had to drive ~170 miles to get it. I then spent ~$1,000 rebuilding it with 3.55 gears, bearings, new axles with 5 lugs and a few other items. I already had the brakes. It's not cheap to build one of these things, that is for sure, but it is fun!

[M22_COBRA]

I did the same as Jeff. Rear end spindles brakes, I'm even using the rear brake lines and allot of misc pieces like some of the brackets. If you are creative you'd be surprised what you can use. Total cost it was $1300 shipped to my door.
I think it was a win given I got a low mile 3.55 drop out.
227311

[Rebostar]

If you haven't ordered your kit yet I'll pass on what one of the instructors at the build school told us.
His thoughts were it's probably cheaper to find a center section out of a 2015 plus Mustang in a wrecking yard this day in age than a regular rear end.
His reasoning was that almost every car sold today has IRS unless it's a pickup.
Also the Mustang rear end handles even supercharged high horsepower Coyotes so it won't be an issue in our cars.

Well said!. I put a supercharger in my 2018 Mustang GT. The IRS keeps the rear end planted right where you put it. Go with the IRS. Though I put a 9" Posi modified to install in place of an 8.8 in my Cobra.

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[Magic Islay Malt]

With the excellent comments and experience shared, I'm now seriously thinking more about IRS.
FBM here has had a number of 2015+ cars in various stages of being parted out and also some full IRSs on the shelf. Most of the postings are assemblies with a 3.15 and feel reasonably priced. I do also see the occasional 3.73 LSD assy but they are twice the price and some and sell quickly.
I'm very budget minded.
How would a 3.15 ratio option feel in a Mk4.
My engine is going to be a mild 302 (GT40P heads, E303 cam, Edelbrock Performer Intake and 600 carb) with a T5.
Mostly street driving and touring with at least one track day in its life.

[Jeff Kleiner]

3.15 ratio was only used in V6 Mustangs and will have a clutch type limited slip. Many of the 3.55 and 3.73 ratio diffs have Torsen limited slip. How will it work? Some of that answer depends on which T-5 you intend to use; the Mustang spec World Class T-5 with a 3.35:1 first gear and .68 fifth or the T-5z with a 2.95:1 first and .63 fifth. The WC T-5 with 3.35 first will work well with a 3.15 rear making for a snappy takeoff without being too short. The .68 fifth gear won't become really useable until 70+ MPH and will require downshifting to produce any real acceleration at speeds below that. The T-5z's 2.95 first will be getting a little soft with the 3.15 rear but will have some long legs. Using a 3.15 with the z's .63 fifth will result in an overall reduction below 2:1 meaning that it will only be useable for flat ground constant speed cruising above 70 mph and any request for more speed will require a downshift. Long story short answer to your question is yes, it will work but won't be "great" My ideal combination is a T-5z with a 3.55 rear. If you're going to use a WC T-5 IMO it is best combined with a 3.31 rear. They were used with 2015 and later V8 Mustangs with automatic trans.

Jeff

[rich grsc]

Hate to be the one but, if you keep trying to cheap out on the build, You are going to end up with an unsatisfactory car. So you save 10-20% on cost, but then in a few years you will have to spend more money and time to correct shortcomings in the build. Build the major parts of the car correct the first time, little add ons and improvements can happen later. If you have too, just wait and save up more $$$$

[Magic Islay Malt]

Thanks again gents, good detailed tech help and some builder philosophical guidance, excellent.
I picked up a T5 at the weekend, its a WC (1352-169) unit from a 1986 GT.
I'll can now keep an eye out for the right IRS.