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Hello,
I'm building Thunderbird 96 with swaped 383W EFI stroker engine. I have Mark VIII for parts and consider what take to my Tunderbird? I noticed the IRS in mark is alloy aluminum, is just as strong as in tbird? I will change differential ratio to 3.73, the alloy body from Lincoln is ok? Any suggestions welcome

Ps. sorry for my english

Thanks
Matt
 

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You can swap the entire rear subframe components, just remember the diff is open, so you'll want a TL carrier. You'll need something to center the springs in the airbag cup, then they work just fine. There are different opinions on the strength of the diff itself, but you'll likely be fine if you have it mounted with pinion brace and rear mount bracing.
 

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The aluminum is not quite as strong a housing as the cast iron; OTOH, if it's a Ford 302W block, the block will split before the ears break off the Mark VIII aluminum pumpkin on an automatic vehicle. OTGH, unless you're striving to keep the weight as low as possible, there's really no big reason to change to a Mark VIII differential; and one reason to not - no Mark VIII had factory traklok. I'd rebuild a cast iron pumpkin for that kind of cubage, personally. YMMV though.

The rear UCAs swap straight across; the LCAs need centering pucks for the springs and will lower a MN12.

Front suspension will swap save for the air suspension parts; there's an extra boss for the switch, but it's not required on the MN12s.

Transmission will be a mod motor bell housing, so it won't swap for you; but you can maybe use it to swap to someone with the DOHC/4V 4.6 and get a Mustang V6 4R70W to build up instead.

If you swap to a 4R70W, and the Mark VIII is a 1993 with the one piece drive shaft, you've got your driveshaft; if it's a 2 piece, I'd recommend getting one built anyway.

Brakes can swap; but that's because they're the same parts.

I'd opt for a Cobra brake upgrade front and back if I were you.

RwP
 

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1994 Cougar XR7 DOHC/5-Speed
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I didnt use anything to center the springs in the cups. I know everyone does it for peace of mind but its really not needed.

The weight difference is pretty negligible between the iron and aluminum cases, for outright strength I trust the iron one more, and it's sprung weight in the IRS, so there arent any dynamic sacrifices for the 15lbs extra it weighs, and its in the part of the car that is too light to begin with - stock weight distribution is 59/41. Even the current IRS Mustangs use an iron case. The control arms are unsprung weight and more worthwhile to use from the Mark VIII, upper and lower.

Plus with the aluminum diff housing you'll need a case spreader if you plan to rebuild the differential yourself.
 

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Discussion Starter #5
My stock diffential also is open, but have new carrier with trac-lock. In this moment have 351W with forged 383 stroker kit+ transmission from Explorer 302. The centering pucks for the springs is no problem, driveshaft moved to t-bird and cobra brakes wait in box to mount ;)
In conclusion :
  • rear differential use from t-bird
  • swap front and rear suspenssion from mark viii
 

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1994 Cougar XR7 DOHC/5-Speed
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Rear suspension yes, but there’s nothing to be gained swapping the front suspension over, other than the airbags it’s the same as a V8 tbird. Also unless the Mark VIII is a 1993 it will have a two piece driveshaft, which isn’t much better than the stock 2 piece steel driveshaft
 
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