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  1. #1

    Default Converting a 7.5 to 8.8, which year and models are a direct fit?

    Apologies if this has been asked 100 times or if I was too thick headed to find what I want to know during a dozen internet searches. I'll start from the beginning.

    I want to replace the factory 7.5 rear assembly in a 84 V8 GT with a complete 8.8 assembly. I have yet to locate clear accurate information anywhere stating exactly which years and model fords are direct fit drop in, if any. If a drop in is available, what else will need modifying, besides brake hose or brake line positions? Is there drop in 4 lug 8.8 with rear discs that will allow me to keep my 4 lug axles/wheels,..I want to upgrade from 29 to 31 spline (4 lug) axles eventually if the replacement 8.8 is 29 spline. Traction Lock is a must. I'd like better gears than the 2.73's... 3.55 or 3.73 gears are preferred.

    Back in the day when I bought my Capri RS 5.0, Motorsports catalog offered new 8.8's complete axle to axle with 31 spines, my cost was about 900$, plus some small parts, rear shoes new drums etc. It was a bolt in replacement for the 7.5 with 3.73's and traction lock diff. With my additional mods to the car, 3.73's really woke the car up. 5th gear kept the car economical on longer road trips and on the highways locally. It's odd to see no one offering a similarly priced complete new or remanufactured drop in 8.8 for early GT/RS Foxes like ours.

    If no new, used or reman 8.8 drop in's exists for four eye GT's/RS's, which 8.8 should I buy and where? What is generally needed to make it work? I repaired cars and trucks for 30 years before retiring in 2011, so I've got plenty of tools and knowledge, but no lift or compressor available. So it is all wrenching by hand on the floor and over a fender these days. The end plan is going with 31 spline axles but still staying with 4 lugs. Reason being is I have 15" mesh wheels I plan to use. No one makes them new in 5 lug. Rear disc brakes are desirable but not essential at the moment. I plan to update front brakes to 88 and up. When I do, I'll be posting for what parts to use, spindle swap etc in.

    I want the total axle length measured to stay the same as the 7.5. I read where the SN95 axles measure 3/4" longer each side, or 1.5 inches total. This would cause issues with tires and wheels I plan to use.

    I live in South Central Pennsylvania, York County. Who, what, or where would be the best place to find the 8.8? Aside from truck freight or a road trip (I own nothing big enough to carry an entire axle without borrowing a truck) are their better options to secure an 8.8?

  2. #2
    FEP Super Member erratic50's Avatar
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    87-88 turbo coupe rear axle give you rear disc but they are the same track width as the SN95 stuff. And imo too wide under a fox

    Honestly ..... if you look at my build thread for my 85 Saleen clone it goes over a lot of disc brake parts required.

    Review the Ultimate 4 lug brake upgrade thread and also the 5 lug thread too. Weight your options.

    Now realize that you can buy 5 lug mesh wheels. They cost around $1000 per set when you find them, but the 4 lug wheels have significant resale value too. The 5 lug opens up far superior parts. Some are 16” wheels which lends to more tire selection

    What offsets the wheel costs is the SN95 brake parts are SO much better and SO much cheaper than the old 4 lug stuff

    I have easily $2000 in inferior 4 lug brake parts for my 85 build.

    I have WAY less in the stuff for my 86GT.

    86 has 94 rearend, spindles, 99GT front brakes and tribar wheels. Wheels with tires cost me a lot less than the 4 lug stuff I bought for the 85.


    Get a 94-98 8.8 rear diff. Get Mosier axles or 5 lug axles sourced from a ranger or Aerostar. North Racecar makes a kit for the axle brackets and parking brake cables.

    Just my open and honest best advice here.

    I can give more details if you need them.
    Last edited by erratic50; 04-22-2019 at 09:25 AM.

  3. #3

  4. #4

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    Thanks Erratic. I'm slowly digesting all the info from the links you posted to check out. Eventually , I sure I will have a bunch of questions as thins have changed in the 20 years since I owned my Fox RS. Back then I ran all 4 lug with the smaller 85 disc drum setup the car came with after I installed the Motorsports 8.8. Brakes didn't feel so bad back then, however I do appreciate how far brake tech has progressed in 20 years, let alone between when my 85 was new and I sold it.

    I appreciate the honesty and wisdom. Perhaps I can find 15" or 16" mesh wheels in 5 lug. The ones I have are 15" 4 lug Black Mesh ARE's (BBS knockoffs),.. I recall they were standard backspacing, with approx. 3" polished aluminum outer lip. Dead Sexy on a Four eye Capri or GT. Thus far, I haven't located these in the 5 lug pattern, I'm sure someone makes/made them in 5 by 144.3, the pattern I just looked up.

  5. #5
    FEP Super Member erratic50's Avatar
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    Saleen used 5 lug mesh wheels starting in 87 when the began adapting Lincoln LSC / SVO brake parts to the foxbody and also making some Frankenstein setups of their own too.

    The 4 lug and 5 lug brake / conversion threads will yield a ton of info.

    Once you get a plan sorted let us know. Always happy to help make sure it’s going to work well.

  6. #6

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    I have a '79 5.0 Hatchback. Swapped to a 3.73 Posi 8.8 rear end. Pretty simple bolt in, but I think I had to mess with the brake lines a little bit. Should be no trouble for anyone with some mechanical skills!

  7. #7

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    Its not the mechanicals that's the issue 79n Fox... At one point I had the tools to do anything even build a chassis and car from scratch just about. I've done my share of Rotisserie G-Bodys, F-Bodys, and Y-bodys among others, had 2 4 eye Fox's (85 Capri RS 5.0 5sp and 84 GT 5.0 5sp) both cars I installed both Motorsport 8.8's w/ 3:73's when Ford sold thew in the catalog. Each was in and moving in about an hour. I don't think Ford sells that rear assembly new anymore, as there are hundreds of thousands if not millions out there used. Once upon a time, recyclers ( think junk or salvage yards) used to have this thing called an interchange manual. It's this huge paper book upgraded each year that tells you what parts on which cars will fit other cars as well, engines, trans, axles, xfer cases, suspension, glass, doors hoods sheet metal, you get the idea. I'm looking for a used salvage yard or pick and pull 8.8 that will bolt under. I can modify the rest. As I don't have a welder anymore, the mounts need to be correct, unless I want to rent a welder or pay someone else to weld the stuff for me, which doesn't save $$

    Erratic's thread and posts above have given me some avenues to investigate and pursue. Before spring I want the parts and a full plan ready to go when I'm ready to swap rears. The brakes as pointed out need upgrading, and it might be nice to go 5 lug all around as well while converting brakes and axle. I may be able to sell my American Racing ARE 398 mesh 4 lug wheels and find comparable 15, 16, or 17, lug mesh wheels. As I said above, there are so many more options available today than there were 20 years ago, not to mention generations of cars newer like the SN95's with other contemporary models that were still on the road back then now arriving in salvage yards. Complete GT40 fuel injected motors were not available back then, they were just beginning to sell Exploders and Mountaineers with V8 option, the GT 40 and GT40P motors are perfect for doing a V8 conversion, and we have the Coyote motors as well, though I'm still a carb guy at heart.

    These cars offer some of the best bang for the buck potential along with decent investment potential, while remaining within the reach of normal folks who don't have the money to afford Barrett Jackson or Mecum level cars. You can still find a solid chassis and 'roll your own' or spend a little more and buy a specific car and restore it or customise it to make it your own. After 25 years of Corvettes, I'm sick of Corvettes, Foxes are much less expensive to own, to buy and to build. Not to mention much more fun
    Last edited by RS_Capri_85_5.0; 12-12-2018 at 10:22 PM.

  8. #8
    Moderator wraithracing's Avatar
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    The simplest option is 86-98 Mustang 8.8's all use the same housing and will bolt into any Fox Mustang.

    The 87/88 Thunderbird/Cougar if equipped with an 8.8 should be the same housing also,

    The disc brake rear ends will be wider than the stock Fox rear track width, so keep that in mind if you want to run WIDE rear wheels. The SN95 brakes both front and rear are the best bang for the buck in regards to OEM Ford. The Cobra brakes, 13" front and 11" rear work very well in a Fox when setup correctly. Although you will have to run 17" wheels.

    I personally convert virtually every Fox I have to 5 lug and SN95 brakes as that options up the wheel options and allows me to run 17-18" wheels that have much better tire options. The tire options in 15" are extremely limited these days in regards to performance. 16" tires are better, but still less than 17/18".
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  9. #9
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    If you go 5 lug, you can get Crown Vic wheels that look very similar to your current ones.

    http://vb.foureyedpride.com/showthre...els-refinished

    PM sent about a Turbo Coupe axle
    '86 Mustang GT T-top. GT40P swap, Maximum Motorsports subframe/coilovers, MGW shifter
    (RIP) '86 Mustang GT, T-top. Cipher's old car
    '91 Wrangler. 4.0, 5 speed, 8.8 swapped, locked, lifted, caged
    -Steve

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