Help me play with my rear end!

My Abnormal 944 currently has a 1995 Mustang 7.5 open diff, 2.73, 31 spline solid axle. This is the factory 4 link geometry - which is not famous for its handling characteristics. I've been using this axle for mockup and so that I can push the car around the garage. But now that I am about to have a running motor, the time is fast approaching where I need to decide what I really want to run for a rear axle and suspension.

My needs are:

1. The axle will never see more than 300hp and probably never race.
2. Gearing of about 3.2 +/-
3. Limited slip
4. “Low” cost

My known options are:

1. Convert the existing 7.5 to desired gear ratio and limited slip. I am not a Ford expert by any stretch but I think there were factory LS diffs in the Bronco II that will work. I am not sure whether the axle splines will mate - my current axles are 31 spline and I believe the 7.5 posi/ls is a 28 spline. If a factory LS 7.5 pumpkin really exists and is truly plug and play then it's probably the cheapest choice at about $300-$400 to acquire and swap.
2. Similar concept to choice #1 but take an entire Bronco II rear axle assembly instead of just the pumpkin. The downside is I would have to do some fab work to equip the new axle assembly with the brackets to tie it into the 4 link. This would probably cost me $500-$750 and take time for all the fab.
3. Replace the entire rear end with the Mustang V8 version from the same era that will have an 8.8, my desired ratio, LS and 28 spline axles – along with the necessary brackets to bolt right in and be the flawed factory 4-link geometry. This would probably cost $750-$1250.
4. Throw most of my existing fab work out the window and buy a 2005+ Mustang rear axle assembly with 3 link, panhard bar. The advantage is getting a 3-link/PBar with better geometry than the older 4-link geometry. The disadvantage is the time it would take to mod my car again to weld in the attachment points for the 3-link. Cost to acquire this model is $800-$1250 and a crap ton of fab time.
5. Other options???

2005+ Mustang 3-Link porn:

A 7.5 will have 28 spline axles so does an 8.8.  The only difference between a fox and up to 04 axle assembly is the axle shafts being longer and disc brakes, the axle housing is the same.

Your best and cheapest route is to just source an 8.8 in the ratio that you desire.  The cheapest one I found was $100, most expensive $600, a lot get pulled to swap to 9" or IRS.  Craigs list or corral.net should get you one in no time.

We run a 7.5 in out lemons car, the LS versions are out there from rangers and other stuff, we kept ours because it is lighter.

Didn't really look at your build thread but assuming you're going V8, you're better off with the 8.8 since it'll hold up alot better, plus there's a fair more aftermarket parts support for anything 8.8 and I want to say even cheaper than 7.5 parts I imagine due to already popular demand on the 8.8 stuff.  

what extra brackets are needed to replace a v6 rear axle with a v8 rear axle? just curious as i'd assume a 8.8 from a similar year mustang would swap straight in

thats what she said

In reply to edizzle89 :

Extra brackets if I were to use a 7.5 or 8.8 out of a non-Mustang vehicle (like Bronco) because of spring perches, lack of trailing arms, etc.

And also extra brackets if going from pre 2005 to 2005+ Mustang because they changed the trailing arm geometry. Lower arms are longer and mount to the body at a wider spacing... etc. So my 1996 era rear axle mounting points would not mate up with the 05+ axle.

akylekoz said:

A 7.5 will have 28 spline axles so does an 8.8.  The only difference between a fox and up to 04 axle assembly is the axle shafts being longer and disc brakes, the axle housing is the same.

Your best and cheapest route is to just source an 8.8 in the ratio that you desire.  The cheapest one I found was $100, most expensive $600, a lot get pulled to swap to 9" or IRS.  Craigs list or corral.net should get you one in no time.

We run a 7.5 in out lemons car, the LS versions are out there from rangers and other stuff, we kept ours because it is lighter.

1994-98 has the same width axle housing as the Fox, but 1999-04 the axle housing is wider than a Fox. Just for clarification.

Or get an entire rear subframe from a Thunderbird or Lincoln for the IRS.  I’ve seen complete hub to hub drop outs for a couple hundred bucks.  

On my Monster Miata I replace the 7.5” 3.27 diff with an 8.8” 2.73 diff for a whole $75.

akylekoz said:

A 7.5 will have 28 spline axles so does an 8.8. 

Can you clarify? Do you mean a 7.5 off of something other than a Mustang has 28 splines? Because the internet keeps telling me that all 20th century Mustang 7.5 rear ends had 31 spline axles.

Sparkydog said:

akylekoz said:

A 7.5 will have 28 spline axles so does an 8.8. 

Can you clarify? Do you mean a 7.5 off of something other than a Mustang has 28 splines? Because the internet keeps telling me that all 20th century Mustang 7.5 rear ends had 31 spline axles.

As far as I know all 7.5 came with 28 spline shafts. The 8.8 in the Fox Mustangs were also 28 spline. The Explorers, F150's, etc. got 31 spline shafts.  

While it's not an 'ideal' solution, isn't it a pretty popular SN95 upgrade to add a Panhard bar to the stock (rubber bushed) 4-link?

What about converting to a torque-arm setup?

Sparkydog said:

In reply to edizzle89 :

Extra brackets if I were to use a 7.5 or 8.8 out of a non-Mustang vehicle (like Bronco) because of spring perches, lack of trailing arms, etc.

And also extra brackets if going from pre 2005 to 2005+ Mustang because they changed the trailing arm geometry. Lower arms are longer and mount to the body at a wider spacing... etc. So my 1996 era rear axle mounting points would not mate up with the 05+ axle.

I get what you're saying, but for his option #3 there shouldn't be any new brackets needed to drop in a v8 mustang 8.8 axle of the same era. So really it should only cost as much as he can find an axle for really.

Driven5 said:

While it's not an 'ideal' solution, isn't it a pretty popular SN95 upgrade to add a Panhard bar to the stock (rubber bushed) 4-link?

What about converting to a torque-arm setup?

I 'think' it's common to remove one of the upper links then add the panhard bar, this eliminates the binding issue with the factory 4 link and still keeps the axle centered.

I think the answer to my rear end playfulness is to use an Aerostar donor. They come with Posi/LS in both 7.5 and 8.8. The hub-to-hub distance is about 62" which is only 3/4" wider than what I currently have in the car. Rigged up for 3-link although the 3rd link is a little unusual for location and in the Aerostar it also tries to function as a panhard bar.  I won't use the factory 3rd link but will try to use the attachment point on the side of the pumpkin. The closest gear ratio is 3.55 and while I'd prefer a 3.27 I'll settle for the 3.55 for now. And it just so happens there's 1 and only 1 Aerostar in my normal wrecking yard and it is an 8.8 posi with 3.55 gears. It also looks like Aerostars have aluminum drive shafts.

If all goes well I am going to skip work on Wednesday and go grab this little guy. I hope its still there!

Now it's MINE!!! Only one small flesh wound from a slipped wrench. 

Does anybody know why Ford put this weird weight thing on it?

It's basically a cast iron dumbell mounted on a bracket to the side of the pinion snout and below the 3rd link attachment point.

For a dynamic systems, you can tune the amount of spring, damping, and/or mass. They chose 'mass'.

Fox chassis Mustangs came with a dog bone shaped weight on them.  I ran into the guy responsible for it at Grattan one day.  Apparently if without it the axle hop from doing reverse burnouts can break the tail-shaft housing on the transmission.  This was found in testing at Ford.  The quad shocks were for forward burnouts, apparently Ford's testing of Mustangs was in preparation for Cars and Coffee.

Sounds like I should start by taking the weights OFF then!

Because - they look weird and I didn't enjoy my dynamics of physical systems class in college.