We just left the local Miata used parts dealer and he has a SBF swapped NA. We were talking about his diff as he wants LSD.
Looks like he has a 7.5 in there. My first thought is swap in an aluminum case 8.8 with LSD. Will the bolt in? The exhaust is real close on one side but it didn't look too hard to modify.
If it really is a 7.5", then you can find a used LSD from a Thunderbird Turbo Coupe or Mustang SVO, Fox body flavor. I have heard that newer Mustangs with the 3.7 came with a 7.5" and could be optioned with a LSD.
What in the crazy swap are you doing? A miata with a miata engine right? How about a Miata LSD or Torsen?
Also I have been running a 7.5 LSD in a Mustang for too many years of Lemons racing, it's lighter than the 8.8 and fine unless you plan on slicks and drag racing.
So here are the pics for mounting my 8.8 alloy diff into the Miata rear cradle.
Basic cradle mod/welding
Rear Mounts on rubber bushings. Note that the differential back cover is a structural component that hold the diff in place. I welded up the angle pieces, but you can just use angle iron to do the same job.
Front mounting points on rubber bushings. Don't forget to dial in a couple of degrees of driveline angle.
akylekoz said:What in the crazy swap are you doing? A miata with a miata engine right?
Nope. He said it was SBF swapped- small block Ford
In reply to NOHOME :
That's real similar to how this 7.5 is mounted. My biggest question is how much bigger is the 8.8 case, are the mount points the same and is the width the same so that the half shafts will fit?
EDIT - Another thought is are the covers interchangable because the mount locates on the cover bolts.
I cannot confirm, but from memory, I do not believe the 7.5 and 8.8 will interchange.
If the guy's got a Windsor in a Miata, methinks it can be made to work.
7.5 is the monster miata setup. I dont think that the 8.8 is plug and play. Axles maybe since I got my axles from Monster Miata. Give Martin at Monster a call and he will clear it up for you. Wonderful guy to work with.
Stampie said:EDIT - Another thought is are the covers interchangable because the mount locates on the cover bolts.
Nope.
One thing to do is see what the MN10 (MN12?) guys do to swap a 7.5 to an 8.8. If it involves swapping subframes, you're gonna have a bad time.
Another thought is that the 7.5 is probably rearend enough. I doubt that you'll fit enough tire in the car to hurt a 7.5. Remember that Fox body drag racers used to run 7.5s because that was all that Ford put in there, and they had more transmission issues than anything, with a heavier car that had much better launching grip.
The 7.5 and 8.8 both have kinda crappy limited slip options because of the way they are set up, but you work with what you got. Looks like you can get a new Auburn diff for under $500, that's going to be ahead of buying something used and then replacing the clutches, and way ahead of an 8.8 swap.
Pete. (l33t FS) said:The 7.5 and 8.8 both have kinda crappy limited slip options because of the way they are set up, but you work with what you got.
Hard disagree with the 8.8 having crappy LSD options. T2R, TrueTrac, all sorts of good options are available. When I had my ESP Camaro with a 10-bolt I dreamed of having the 8.8/TrueTrac diff from my Supercoupe.
That said, I've had five MN12-platform cars over the years, so I was initially tempted to say "Sure, the 7.5 and 8.8 both came in the T-Bird, so they should be interchangeable." But I've never actually had one with a 7.5, so I can't say for sure. This thread, though claims it's a direct swap.
In reply to Will :
The issue is just that they use a weird S spring for preload, and they engage the clutches by the way the side gears force against the spider gears. It "works" but is uncouth compared to the way, say, a Mazda clutch diff works, with a separate gear carrier that acts on the clutches, which can have their preload adjusted independently of whatever the differential gears are doing, and the thrust ramps can be adjusted independently for acceleration and deceleration, whereas the Traction-Lok is entirely down to the angles of the side/spider gear teeth.
It's all due to the diff having to be designed to have two spider gears and a removable shaft, to accommodate C clip axles.
Also, the Traction-Lok uses fiber clutches that wear a lot faster than the metal on metal clutches in the other type.
In reply to Pete. (l33t FS) :
The TrueTrac and T2R don't work that way, though.
Any Reason he wouldn't just go with the 7.5" Truetrac? There hasn't been a real issue with the 7.5" in the monster miata applications.
Finally, a question I have first hand knowledge of and can give useful information.
A few years back I bought a broken Monster Miata and brought it back to life. It had the 7.5 open diff from a 94 Thunderbird 3.8 and geared for a 3.27:1 ratio. It made for ridiculous one tire fire burnouts but never really hooked up.
I found a 8.8 center diff from a similar year SuperCoupe with the TruTrac and 2.73:1 gears on CL for something like $90. Firstly: the axles and driveshaft both work just fine. Unfortunately the crescent shaped piece doesn't line up with the diff cover holes in the 8.8" unit. An couple of hours with an angle grinder and drill made it work out though.
Hoisting the diff in and out over and over got super tiresome so eventually I dropped the rear subframe to make the fitting up process go a bit easier.
The upshot is that it can be done but it isn't easy or quick.
SV reX said:akylekoz said:What in the crazy swap are you doing? A miata with a miata engine right?
Nope. He said it was SBF swapped- small block Ford
For the pedantic, "Small Block" and "Big Block" traditionally describe two different Chebby engine classes (that have parts that will fit either). Ferd's were "Windsor" "Cleveland" "FE" and switched to "385" for their honkin' 429/460. Next to nothing interchanges, including different years / models of same family! 
Anyway, back to the rear end discussion...
Small Block Ford = Windsor
Big Block Ford = (usually) 385
Pretty common terms to hear across cardom.
In reply to buzzboy :
To the youngsters, yes. These days, I hear a lot of stuff. I've even tracked (through different years of webesters laying around) the degradation of language in the US. Websters even supports the use of "to decimate" as proper for "completely destroy" (um, "deci"?)
Chebby corporate used the word "Small" and "Big" as designations. Ferd never did, back when parts were looked up in books.
'Course I was around when people were still racing FE's, so I don't understand very many of the made up words in rap, either. 
buzzboy said:Small Block Ford = Windsor
Big Block Ford = (usually) 385
Pretty common terms to hear across cardom.
Technically, 221/260/289/302 are not Windsors, just like 400s are not Clevelands. IIRC they are just called the Fairlane V8.
Pete. (l33t FS) said:buzzboy said:Small Block Ford = Windsor
Big Block Ford = (usually) 385
Pretty common terms to hear across cardom.Technically, 221/260/289/302 are not Windsors, just like 400s are not Clevelands. IIRC they are just called the Fairlane V8.
That is correct, till the 351 of the series started (I totally forgot the Fairlane V8 was the original name - but did know that, many brain cells ago!)
I often hear the 400 miss called a 400M, but it's not. It shares a lot with the 351M, that shares a lot with the cleavland, but Ferd never used the M for the 400!
Ferd always did weird stuff !
The 7.5 and 8.8 thunderbird diffs are a direct swap to the mounting points, width, axles, and driveshaft as KyAllRoad mentioned. You can see my thread HERE for pictures of my setup. I've had both installed without modification.
In reply to Shavarsh :
Haven't looked at the bean thread in a long time. Page it went to mentions "passengers will loose about 4" leg room"
Ive ridden in the back... didn't know that was more than 4" NEW! 
great to hear facts from a guy that's done it! (And to bring the topic back from me being funny)
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