Rear end choices?

[VKannan]

Hi all,

My kit build date is mid March so I have quite some time to be patient and find good deals on parts. I am trying to figure out what my options are for a rear end. I'll either be using a 302 with Sniper EFI and T5 transmission or Coyote with TKX. The car will never see the track, and needs to be comfortable on long highway trips. Due to budget constraints I'm going with the 3-link. Here are the new parts options I see for rear end:

1) Forte's Moser Engineering 31 Spline 3.55 Gear 8.8″ Rear End Assembly $2,572.00
2) Factory Five option 16204 - Moser 8.8” 3-Link Solid Axle Rear End Housing, 3.55 Gears with 5-lug Axles, Standard Width (price includes $499 S/H) $3,134.00

Two quick questions:

First, what is the difference between the two? Do I also have to buy rear brakes with either option?

Second, is there a donor option that would be significantly cheaper? If I go with the 302 I won't have much power so I'm not sure I need a very beefy setup. If a donor option exists, what specifically do I need to look for in terms of Make, Model, Year, Trim, Options, etc?

Thanks!

[JeffP]

My understanding is they are pretty much the same. Forte's requires some fabrication of the 'banana bracket' whereas FF's will come with it welded on. you can do the fabrication yourself although there are some critical angles in the process or you can send your banana backet when you get your kit to Forte and he will weld it on for you. I bought mine from Forte along with my Coyote and he took care of the bracket.

[Theshandman]

Good questions, VKannan. I opted for the BPE 347 / Sniper, TKX with the F5 Moser 8.8 3-link rear option. I've go-karted and it rides fabulously smooth. Like you, I have no plans to track it and frankly, the 347 has more than enough power for me. Can't talk to your other Q's other than I opted for the Wildwood brakes upgrade option. Glad I did.

[egchewy79]

you'll need brakes w/ either option, unless you get a salvaged rear end that comes w/ brakes.
I looked into junkyard 8.8"s and it was just easier to go the Forte route. As mentioned, if you get your rear end after your kit, you can ship the banana bracket to Mike and he'll weld it on for you.

[VKannan]

Curious, what made it easier to go the Forte route? I see local adverts for things like a "rear axle from 1994 Ford Mustang GT 5.0L, 8.8 Inch, 3.27 Gear, Limited Slip Differential, 28 Spline axles, 5 lug" for $300 but I wonder what all would be involved in making that work for my application. Would it fit? Any significant modifications? Should I get it rebuilt and if so how much does that cost and what kind of shops do that?

I'm very lost, unfortunately.


you'll need brakes w/ either option, unless you get a salvaged rear end that comes w/ brakes.
I looked into junkyard 8.8"s and it was just easier to go the Forte route. As mentioned, if you get your rear end after your kit, you can ship the banana bracket to Mike and he'll weld it on for you.

[Morrisett]

I used a 8.8 out of my 97 cobra donor and it already had new gears 3.55 so that was a plus. You’ll need to end up narrowing it which there’s several companies out there that sell you the axles and brake brackets to do that. I replaced all seals and bearings at that time as well. https://www.northracecars.com/vintage_brakes.html

[CraigS]

You can definitely do it cheaper but there are so many options that you need to know about. There is no single year Mustang axle that has all the best stuff included. I am not going to run all this down because I really can't remember it all. The early axles were the correct width up to maybe 95 and then the axles got longer to push the wheels out some, and a couple years later the housing itself got wider. Brakes were another problem. You had to get to 95(?) to get discs but although better than drums, even those disc really are not adequate. Ratios are another ? None of the Fox Mustangs had a ration you would want. They were all real tall trying to go for gas mileage for the epa #s. A 355 is probably the most popular ratio so you can see that a stock 2.70 or 3.08 isn't great. I 'think' the one you listed would work fine but it would be good to check the width. Usually it is measured from flange to flange so you need to get that number to compare. If the width is right the other specs will work for you. I hope others will chime in to this thread to provide better details.

[BEAR-AvHistory]

Curious, what made it easier to go the Forte route? I see local adverts for things like a "rear axle from 1994 Ford Mustang GT 5.0L, 8.8 Inch, 3.27 Gear, Limited Slip Differential, 28 Spline axles, 5 lug" for $300 but I wonder what all would be involved in making that work for my application. Would it fit? Any significant modifications? Should I get it rebuilt and if so how much does that cost and what kind of shops do that?

I'm very lost, unfortunately.

You would be looking at a piece thats about 28 years old. Think installing without a total rebuild especially with wear parts like an LSD is a crap shoot. As long as you need to go through a rebuild process might as well get one modified specifically for the car. To have a successful long term out you need to be very careful of cheaping out in the drive train.

[Mastertech5]

I bought a junkyard rear end out of a 1989 Fox body mustang. They are the correct width,1979 - 1993. The SN 95 mustang 1994 - 2004 is a little wider. Then when they went to rear disc and ABS they got a little wider. Like Craig's said they ratios aren't great. I upgraded mine to 3.55 ratio 31 spline axles all new bearings and a new limited slip center section. Everything new except the housing. I took the drum brakes off and bought 11.5" 2004 Mustang Cobra rear brakes from CJPony Parts in an everything kit. You need to buy 21 inch braided steel flexible brake lines as the ones they send are too short. They even give you the needed brackets to convert to discs and spacer rings for the rotors as the center hub of Fox body axles are smaller than SN95s. I did the mods myself, but I was a Tech for 45 years and have the tools to do it. I would advise you to have a Ford dealer do it if you go that route. I spent around $1500 complete and another $500 on the brakes. You would have to add for labor. IMO a FFR or Forte unit would be the better choice for you. The Moser tubes are thicker and are welded to the center section. You can go with a newer, wider rearend but need to compensate with a larger back spacing on the rear wheels.

[VKannan]

Love this forum. Sounds like this is not where I want to try to cut corners. I’ll get one of the options made for this car. Thanks everyone!

[GoDadGo]

Love this forum. Sounds like this is not where I want to try to cut corners. I’ll get one of the options made for this car. Thanks everyone!

Moser Engineering built my Dana 44 because I wanted something different.
They adapted the assembly so that it fit perfectly and utilized, at my request, Ford Explorer brakes.

[egchewy79]

Curious, what made it easier to go the Forte route? I see local adverts for things like a "rear axle from 1994 Ford Mustang GT 5.0L, 8.8 Inch, 3.27 Gear, Limited Slip Differential, 28 Spline axles, 5 lug" for $300 but I wonder what all would be involved in making that work for my application. Would it fit? Any significant modifications? Should I get it rebuilt and if so how much does that cost and what kind of shops do that?

I'm very lost, unfortunately.
After pricing it out, the cost of an appropriately sized rear axle and a rebuild kit would have cost around $1500. I would have also had to grind off old brackets and weld on the banana bracket. At the end of the day for me it was easier to buy a complete package from Forte. Also setting the pinion pre load is a bit tricky. That being said, I’m currently rebuilding a ford 9” for a truck project I’m doing. I guess with experience comes confidence��

[edwardb]

I'll put my IRS sales hat on just for a second. On the surface the 3-link looks like a much cheaper option and it certainly can be. Yes there are salvage 8.8 solid axles out there that are the proper width. But as pointed out, they're old and typically need major rehab -- both cosmetically and mechanically -- plus often the ratio changed. DIY can be reasonable (I've done it) but if you're paying someone for the parts and labor the units from Forte or Moser aren't a bad deal. Also as pointed out, the Moser axle is probably a bit superior because it has thicker welded on axle tubes and the welded banana bracket. It's a quality piece. I have one in my truck build. But at that price, you're approaching the cost of IRS. Buy the IRS option from Factory Five. That gives you the proper frame setup and most of the parts. You can find ready to use center sections, knuckles/hubs, and brakes in salvage for the IRS for a very reasonable amount. They're plentiful and typically only a few years old. The IRS super 8.8 is more robust than the solid axle 8.8 and normally can be used with no further work required. Multiple current model Mustang brakes can be used with no modifications if not included with the salvage parts. You state you want the build for cruising and comfortable on long highway trips. The IRS will maximize that. I've had both and the IRS gives a noticeably better ride. The rear suspension is something that can't be changed. Find another place to save on the build that can be changed or modified later if you have to.

IRS sales hat off. :cool:

[Sarcasticshrub]

I've spent the last 10 months thinking through this thought process myself. I ordered a kit in Feb., looking at Dec. delivery. Plenty of time to create too many spreadsheets showing the possible cost-vs-time-vs-extra work involved in each and how I want to spend the $$ to get the car I want to drive. Donor parts or new? IRS, 3 or 4 link?

I originally ordered the 3-link option with the thought of keeping the upfront cost down, and rebuilding a donor 8.8". As edwardb points out, the IRS is not that far off the budgetary mark when you start to look at all the different ways costs/time could pile up on the other end. Long story short, my spreadsheet investigations (and spending a ton of time in this forum and others) pointed to the IRS as the best option to save me time and hassle, and get the overall driving experience I want for just a few dollars more (in the grand scheme of things). :)

[VKannan]

Could you work through the math on this with me? What is the actual, final cost difference between the two options and the breakdown? Would love to see how this works out on your spreadsheet. I could be convinced if it wasn’t that much different…


I've spent the last 10 months thinking through this thought process myself. I ordered a kit in Feb., looking at Dec. delivery. Plenty of time to create too many spreadsheets showing the possible cost-vs-time-vs-extra work involved in each and how I want to spend the $$ to get the car I want to drive. Donor parts or new? IRS, 3 or 4 link?

I originally ordered the 3-link option with the thought of keeping the upfront cost down, and rebuilding a donor 8.8". As edwardb points out, the IRS is not that far off the budgetary mark when you start to look at all the different ways costs/time could pile up on the other end. Long story short, my spreadsheet investigations (and spending a ton of time in this forum and others) pointed to the IRS as the best option to save me time and hassle, and get the overall driving experience I want for just a few dollars more (in the grand scheme of things). :)

[CraigS]

You would need to check the current FFR IRS option pricing to compare. I did an IRS retrofit in 2017-2018 replacing the 3 link in my MkII. The kit from FFR at the time was $2400. I also spent $1000 on a complete rear suspension takeout assembly from a salvage yard. In addition to giving me IRS, I made sure to buy a salvage unit that included the brakes. Bingo-really great rear brakes for free.
175320

[rich grsc]

Go IRS. It's just a little more, but the ride and handling more than make up for it.

[CaptB]

If you buy from Forte he welds the bananna bracket on for free.

[Jeff Kleiner]

...is there a donor option that would be significantly cheaper?
Thanks!

Yes! I've done this on multiple builds but it requires you do do a little legwork rather than pushing the "Easy" button for one stop shopping:

Pick up a salvage 8.8 rear with Trac-Loc from a 1987-1998 Mustang for $200-$350 (Last one I did 2 years ago was $250)
Buy a set of caliper relocation brackets from North Race Cars for $510
Buy a ring and pinion in the ratio of your choice along with their package that includes bearings, seals, shims and lube from Late Model Restoration for $270
Add a Trac-Loc rebuild kit from CJ Pony Parts for $95

If you don't have the ability to perform the labor yourself the going shop rate to do it all on a loose rear end out of the car will run you about $300. Pay a welder 50 bucks to stitch weld the banana bracket and you end up with virtually the same end result for right around half the cost of the Moser option. Either one still has to have brakes added.

If you're going to do the IRS vs 3 link cost comparison first determine which option you would go with on the solid axle; Moser or Forte for + or - $3K or used rebuild for around $1,500.

Jeff

[VKannan]

What year/model cars should I look for when going that route?


You would need to check the current FFR IRS option pricing to compare. I did an IRS retrofit in 2017-2018 replacing the 3 link in my MkII. The kit from FFR at the time was $2400. I also spent $1000 on a complete rear suspension takeout assembly from a salvage yard. In addition to giving me IRS, I made sure to buy a salvage unit that included the brakes. Bingo-really great rear brakes for free.
175320

[edwardb]

What year/model cars should I look for when going that route?

Mustangs 2015 and newer. The newer you find will likely have lower miles and a better chance to be in good condition. The center section has several variations. The main case material can be either iron or aluminum. Either is OK. There are multiple ratios. 3.55 is by far the most common and what you would get new from Factory Five if you ordered from them. You would be safe to choose that ratio. But you have time to do your homework and determine the best ratio based on engine, trans, tires and planned use. Limited slip options are either the usual clutch packs (similar as a solid axle 8.8) or a geared version called Torsen. The Torsen setup, while nice (I have it my Coupe), likely would be a significant cost increase. For your driving the clutch pack style, Ford calls it Trak-LoK, would be fine. What most have.

[JeffP]

Basic math I did for my build, I wanted Wilwoods - and that adds to the difference significantly.
IRS
Kit Cost $2800
Center $1600
WW Brakes $2299
Total $6699

3LINK
Kit Cost $0
Moser $3134
WW Brakes $1075
Total $4209

So for $2300 less, I went the 3link route. For apples/apples - these are all prices taken straight from FF. Yes, you can do cheaper elsewhere which may impact the delta.

[John Ibele]

Your "needs to be comfortable on long trips" comment says IRS. You're close to sitting on top of the rear axle, and you'll be getting as much cushion from the road as possible in this car with this option.

I have the older (pre-2015) IRS, and certainly focused on budget and overall cost during the planning phase of the build as you are. That's important, but for many builders, this gives way - after the initial kit purchase - to a spend rate aligned with the pace of build. I'm pretty sure very few builders spend what their initial spreadsheet indicated.

Point is, make sure the initial choices which can't easily be undone or upgraded later really align to your intent for the car when it's on the road.

I prioritized ride quality as well, but other things had to give to meet the budget. I went with a 347 and a T5. Stock GT brakes as well, since I wasn't going to be repeatedly hauling the car from 100 to 30 mph, and could always upgrade later. 8.8 center section from a salvage yard, and rebuilt with 3.55 gears myself. While I sometimes wish I had the Wilwoods under me for stopping power, I think the priorities were right.

Not trying to 'sell' IRS actually, just pointing out the alignment to your comment about ride quality. You may have other considerations driving your focus on other options. Hope that helps and good luck with the build planning ... it's definitely part of the fun!

[GoDadGo]

The IRS will give you a better ride and improve overall handling; however, if I ever do another build I'd still go with the 3-Link. ..It plants the tires very well and allowed me to shorten my wheelbase so that the rear wheels could be centered within the wheel arches...The set up is so simple that even this "Chevy Guy" could install it.

https://youtu.be/9WEe6-wdNtA

What ever rear set up you choose will be a winner so consider the ride quality and handling over the simplicity and ability to launch the car hard and straight as the determining factors...Having ridden in cars with both set ups, your back will appreciate the I.R.S. if you have spinal issues.

Good Luck & Happy Wrenching!

[nucjd19]

Just my opinion. I have a 3 link I ordered from FFR. It is awesome and is not the rate limiting step regarding the top performance of my rig.... It is the pilot :) But if I could do it again I would have went IRS. The main reason is resale as that seems to improve resale value. I am sure reading from multiple posts that the IRS is a better ride but I have no comparison so I know only what I know and my roadster is just amazing. So you can't wrong either way unless ....you are Mr. Kleiner and his ilk who are autocross machines. Now they could find the differences very quickly and display them for everyone to see :)

[CraigS]

I will throw in one more plug for IRS. I know you are real far from thinking about this now but IRS will add resale value. If I were looking to buy a completed FFR I wouldn't even consider a 3 link.

[GoDadGo]

> If I were going to build another Factory Five, and I hope one day I will, it would have the 3-Link.
> I can honestly say that once I completed my 3-Link MK-4, I sold my beloved 1995 Corvette.
> The roadster easily out accelerated, out cornered and out stopped that old Vette.
> The simplicity of the 3-Link set up just works extremely well with no drama.
> Keep It Simple Stupid (KISS Design) is really the beauty of the 3-Link.

Gone But Not Forgotten:.. https://youtu.be/svZX2BMSDEs