to start with, I've been checking this out off and on for a couple weeks, so yes I've searched it to the nth degree

I haven't verified it myself by hand yet, but I've run across a fair amount of information pointing to the 8.8 being very simliar to the 12 bolt, some old timers have even told me that their ring gears are so similar that the early 8.8 aftermarket sets were just redrilled 12bolt gear sets

now I know the advantages of a purpose built aftermarket rear, suspension bolts in, ect., but the cost is the big downside

I do know most yards have the 8.8 axels for cheap, and the mustang guys even make some aftermarket torque arm setups that would bolt up to the 8.8 and probably fit a third gen with some modification, or build your own, either way it can be done

the only real problem I've found are that the 8.8 can be converted to a 5 lug on 4.5 patern with stock ford parts, usually from donor vehicles right in the salvage yard, and I believe aftermarket axels could be had for 5 on 4.75 to fit the housing (i believe 12 bolt axels are the same as long as the length matches) but I don't know if it would be possible to to fit brakes without it being cost prohibitive

anyway, has anyone done this, I've seen bits of info on some of the ls1 forums about it, but very little and its spotty, plus the forums I found it on are kind of restricted

basically, i'm cheap, I'd like it all for nothing or as little as possible, and honestly I get the biggest kick out of trying to get the most speed with the least cash so scoring a 300$ five on 4.5 pattern mustang 8.8 with posi, gears and some cheap disk brake options seems a step ahead of 2000$ for an aftermarket 12 bolt or worse

I'd appreciate anyone with anything to offer, thanks

oh, ps, dig the board, kick*ss info in general

 

Ford 8.8 is similar to a 9". They're available in 28 spline for drum brake cars or 31 spline for disk brake cars so you're not going to find 12 bolt axles which are 30 spline to fit but you can order aftermarket axles in whatever bolt pattern you want. The 8.8 and 9" axles are bolted on from behind the backing plate. 12 bolt axles use c-clips on the end so even with c-clip eliminators, the axles won't fit.

Converting 4 bolt to 5 bolt rims axles is possible with junkyard parts however the cars for donor axles are old and hard to find. It's better to just buy new axles.

A few custom rims such as Weld Draglite have a dual bolt pattern so you can use them on the Ford 5 on 4-1/2" or the small GM 5 on 4-3/4". My front wheels are GM and my rear wheels are Ford bolt pattern.

Finding and using a junkyard 8.8 is no different than finding and using a junkyard 9" or 12 bolt. First you need to find one close enough to the third gen's diff width. Then you need to find some way to adapt or eliminate the torque arm. There is no easy way to install a good torque arm mount onto a junkyard diff. If you do have some good fabrication skills and manage to make something work, it can cost you more than what it would cost to just buy a bolt in aftermarket housing. Even if you eliminate the torque arm and LCA by converting the rear suspension to ladder bars or a 4-link, that's all extra cost to the diff swap.

Options

1: Buy an aftermarket 9" bolt in housing with axles for around $1000. Install a junkyard center section.

2: Buy a junkyard diff of your choice. Buy new axles, fabricate or convert your rear suspension to use the junkyard diff. Convert the brake system to GM. I'd say buy new rims but with new axles you can still use your old rims if you keep the GM bolt pattern. If you get axles with Ford bolt pattern to easily use Ford brakes, buy new rims that use the Ford bolt pattern. Spend more money than option 1 but can say I did it myself to save money.

 

The 8.8 is similiar to a 12-bolt in several ways, but the parts are all different.
(why would Ford be using "re-drilled" GM 12-bolt gears?) The 8.8's do have c-clip axles, but again, Ford is Different than GM. The comon 8.8's all have 28 spline, even the Mustang GT/Cobra. Some trucks got 31 spline, but the axles are to long for any benefit, though if you happen to find a truck with a 31 spline posi, that could save you a little $ if you really think you need the larger axles. Many low 10 sec 8.8 eqiuped cars are still running 28 spline, just aftermarket.
As Stephen said, adapting it to our car's becomes the trick part. The cast housing is not very receptive to mounting a tq arm. The Maximum Motorsports and Granatelli mustang arms are very different than ours and would require probably as much work to mount as building a custom arm.

The stock posi units leave much to be desired. You'll need either the correct bolt pattern wheels, or aftermarket axles with the correct pattern, plus width may need to be addressed, depending on the housing you aquire. Then add in all the time/money spent to get it all mounted in......that Moser 9" starts looking pretty cheap. - Bottom line, it can be done, but is very difficult, possibly fairly expensive, so it may or may not be worth it.

 

BOTH the 8.8 and the 12 bolt have the same type axle, both c clip, and....they even have the same axle bearing (timken 8660S, although there is more than one bearing for the 12 bolts, but they common bearing for both is the 8660s) don't believe me, go to the timken website http://www.timken.com/industries/aut...rtCatalog.aspx
and check out the rear wheel bearing for a 80s mustang and a mid 70's chevy half ton truck, now even though the bearings are the same, i believe the axel housing ends are different, so brakes wouldn't swap, but just the shaft and such of the axels interchanges, and like you both said, the stock posi from anyone isn't that impressive, i'd run a trutrac anyway

I didn't say ford used chevy gears, read more carefully, I said some aftermarket company's were selling gears for the 8.8 ford that were actually redrilled 12 bolt ring gears, the 12 bolt is 8.875 i believe, so thats pretty close, and the tooth count and pitch matches, not totally sure, but a story i've heard more than once from old timers that called the 8.8 a ford 12 bolt

also, the part for the 5 lug swap aren't rare, they're ARB (aerostar, ranger bronco) they're more plentiful than the mustangs probably

really what i was asking was if anyone knew of a GOOD reason why guys aren't using the 8.8 besides fabbing the housing into the car in the first place, the 9 inch housings are pretty heavy, and for road applications you really want the lightest rearend that won't break, so far the only hurdle i'm seeing is finding a brake setup that will work without swapping housing ends, and I think you can even get different housing ends from moser for like, 80 bucks, I'm just thinking that there is a power level the 8.8 could live up to thats beyond the stock rearends, but still lighter and a bit cheaper than a 9"

 

My mistake on the 8.8 axles bolting on but you're still looking at different spline counts for 12 bolt and 8.8 so a GM axle still won't fit.

Even though the ring gear size is close, that still doesn't make it the same. What's the pinion height of a 12 bolt? What's the pinion height of an 8.8? If not the same then the gear cut will be different. What's the pinion size and spline count of each?

GM and ford make a 7.5" but they're not the same nor do they use the same gear set.

The extra weight of a 9" is mostly in the center section. You can easily make it lighter than a GM diff by using an aluminum case. There's a very slight hp loss through the 9" but for most people, they'll never notice the difference.

Advantage of the 9". Parts are cheap. The same carrier uses all the gear ratios. There's no series for different gear sizes. You find a carrier that has 2.50 gears on it and you can put 5.13's on it.

As I already mentioned, if you're going through all the trouble to convert some other sort of diff, why not just do a 9". It's going to cost you the same and the 9" will be better. If you don't feel you need the strength of a 9" then just run the tiny 10 bolt. It will last longer than most people think.

Why not do an overkill and modify a Dana 60? In stock form, it's unlikely you'll ever do any damage to it.

You're barking up the wrong tree trying to install some other none standard diff. You could just as easily install a Dodge 8.75" diff if you wanted. People chose the 12 bolt or 9" for a reason. Parts are cheap and easy to obtain. The diffs are strong with very little modification.

 

There was a guy here who did it, didn't you find his threads in all your searches?
He was even going to go about selling his setup, but lack of interest stopped him. He sold his 10 or so proto's to 4th genners. Find his thread(s), he had schwacks of info on it.

 

An 8.8 is 28 spline or 31, the 12-bolts were 30. The factory axle lengths would more than likely also be wrong. - I'm not trying to disrespet you in any way, just pointing out the flaws in the "8.8 is a 12-bolt" theory. They do have some similiarites, but are very different. As Stephen said, "GM and ford make a 7.5" but they're not the same nor do they use the same gear set.'

I too believe the 8.8 is a tough rear, and can be had fairly readily for a decent price. I am even considering utilizing one myself. But, I have the knowledge/ability to fabricate everything I need myself, thus eliminating the extra costs involved (labor doesn't count when you're on a budget).

Stephen pointed out most of the reasons behind running a 9", so I'm not gonna re-hash that. I will point out that the 96+ mustangs were also factory 5 lug cars, 5x4.5 though. I'm working on a buddies 68 stang right now that we're doing tube frame rails and a tq arm rear suspension and late-model strut front. Since it's recieving an 8.8, I'm already in the works with the tq arm bracket.......

 

as per your request chevelle guy:

tidbits of info (sourcing the 8.8")
https://www.thirdgen.org/forums/tran...light=ford+8.8

length specs-
https://www.thirdgen.org/forums/tran...light=ford+8.8

THE thread, the guy who made them, etc. All 3 pages, GOBS of info
https://www.thirdgen.org/forums/tran...light=ford+8.8

 

I'm not sure how i didn't find that, much appreciated, extremely helpful

 

Just posting to keep track of the info!!