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  1. #1
    FEP Super Member erratic50's Avatar
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    Default Adding rear discs while staying 4 lug

    The stock brakes on the 1986 GTs SUCK so I am currently researching a way to help my son switch his 1986GT over to rear disc while staying 4 lug and retaining ebrake.

    His budget is very tight so no exotic kits or parts are in the works. Stock 10 hole rims and tires will be retained.

    I am currently considering the idea of putting on Fox adapters for SN95 calipers then redrilling the SN95 rotors for four lug simply because this looks like it might be the cheapest and easiest to source option.

    Does anyone know of an off the shelf 4 lug rotor that will work with an SN95 rear disc setup?

    I know there were Thunderbird Turbo Coupes that came 3.55 rear gears and 4 lug 4 wheel disc brakes. That as a rear diff swap is perhaps an option but that is one rare donor car! (And has a wider track width afaik)

    Lookibg for thoughts and ideas. Thanks in advance.

  2. #2
    Moderator wraithracing's Avatar
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    Probably the best option IMHO. Nothing exotic and all the parts in one place.

    http://www.northracecars.com/Brakes.html
    ​Trey

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  3. #3
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    Trey is right on the money. I have their brackets and they work fine.

    If I have a need to do it again, I'd buy their brackets with the e-brake cables and then pick up my own calipers, rotors and hoses. Those are simple to source from your favorite retailer (or boneyard). The soft lines I used were standard SN95 rear. I think I had to use an adapter between the hard line and the soft line.
    '85 GT

  4. #4
    FEP Super Member erratic50's Avatar
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    I like the brackets and cables only idea - it's along the lines of what I was thinking.

    Any info about off the shelf rotors that will work with the SN95 calipers and hoses?

    Perhaps we should make a sticky "ultimate" thread for this too. Lots of guys out there who don't want 5 lug. We all need to stop unless we want a smashed four eyes ride.

    Not looking to boil the ocean, just make a four eyed fox stop. I am simply hoping to get braking on par with the average 2004 minivan or slightly better. (sadly that would be a huge improvement)

    Better brakes are like anything else though. We say they are enough until they prove otherwise. I wish it were easy to make a 4 lug car turn and stop like my 5 lug converted car but I know that that is far from easy or cheap.
    Last edited by erratic50; 05-07-2017 at 12:53 PM.

  5. #5
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    Quote Originally Posted by erratic50 View Post
    I like the brackets and cables only idea - it's along the lines of what I was thinking.

    Any info about off the shelf rotors that will work with the SN95 calipers and hoses?
    From the Brake FAQ's on that site...

    What do I need to complete the install?

    First, remember, nothing is interchangeable: There is no such thing as 5 lug rotor for a T Bird caliper. There is no such thing as an 11.65 inch 4 lug rotor. Please remember this; it is very important NOTHING is interchangeable!

    All of our brackets include the hardware and instructions are available in the links beside each kit. The parts needed are listed in the instructions. In short, calipers hoses and rotors are from the car whose brakes we are duplicating. The 4 lug will be 87 Thunderbird. The 5 lug conversions will be 94 GT Mustang or 94 Mustang Cobra. It is really that simple. The soft lines etc should come from 94 GT the calipers are 94 to 04.
    To stay four lug, the parts you'll need beyond axle brackets and rear cables will be:
    From Rock Auto, unloaded T Bird rear calipers can be had for about $45.00 each with the core and the rotors can be had for about $25.00 each. Hawk HPS pads from Amazon are less than $60.00. Rear hardware kit, from Rock Auto again $10.00 or less and still at Rock, the '95 Mustang rear hoses are less than $10.00 each.

    Don't forget the aftermarket rear prop valve and plug for the stock prop valve. BTW, I did need an adapter for the hard to soft line in the back. I don't remember what the specs were but I now recall I got them from Maximum Motorsports when I bought the prop valve and plug.
    '85 GT

  6. #6

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    Turbo coupe rear would be the ultimate donor car for several reasons. It is the only 4 lug rear rotor(except 93 cobra which also used the turbo coupe rear end). 3.55 (manual) or 3.73 (auto) ratios on a 8.8" traction lock rear with quad shocks. The negative is that it is about 3/4" wider per side.

    You can also flip the brackets side to side and that will get you close to the same width as the stock stang, and then maybe use a few shims to line everything up.

    The hard part is getting the brackets. The other brackets work, but if you wait long enough, a parts car can be found. Ive seen a few in the $200 range with no motor or trans, and have seen as many as 4 in the scrap yards locally in the last year or so.

    Ranger, sand rail and svo guys part them out for engine/trans swaps then just let the rest go cheap.

    Also the early 90's taurus used the same rear calipers for a few years, should be plentiful if you need any cores.
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  7. #7
    FEP Super Member erratic50's Avatar
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    Not above good condition used parts. Used rubber brake lines is a clear spot to draw the line. I shy away from parts removed and left sitting in a box open to the elements for anything other than cores, but frequently used calipers and rotors off a junk car are fine if the look OK. Have done that many times and it only burned me when the parts sat around in a box before I put them on.

    Looks like new stuff will set a guy back about $550

    Good info so far. Anything to add?

    Will the stock master cyl work out best or will going to a 15/16" or 1" bore be better?

    Any multi-piston calipers known of that work with the 86 front spindles? Or something more than pads that improve those pieces of junk?

    if anyone has or knows of a Tbird rearend that's in need of a new home please PM me.

  8. #8
    FEP Power Member bluesfannoz's Avatar
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    Pretty sure he still has this

    http://vb.foureyedpride.com/showthre...ht=turbo+coupe

    I have just about everything else you would need to go along with it.
    Steve
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  9. #9
    FEP Super Member erratic50's Avatar
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    Interesting link. I get to the Kansas City area frequently - it's about 300 miles away. I asked for pics, also if the brakes are included.

  10. #10
    FEP Super Member erratic50's Avatar
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    Did some looking on a few other forums.

    A few have had success adding rear discs by using fox 4 lug axles, adapters for SN95 brakes, SN95 calipers, and SN95 rotors -- redrilled. They cut a 5/8" hole for the 1/2" studs mimicking what's commonly done on hub centric dragster brakes. Those, of course, are done that way due to heat expansion.

    I had stuff around and just had to look. If you use one existing hole you have to weld one in as another bolt hole will partially line up. If you don't use any existing holes the approach is mark one and drill it 1/2" then knock 3 studs out of a 4 lug rotor and drop the rear rotor over the front rotor hub and bolt together then clamp the mess into a press and drill the other 3 holes, then go back and oversize the lug holes.

    Interesting approach.

    the bad: Replacement rotors are not off the shelf - process needs to be rinsed/repeated if you need to replace rather than simply turn rotors. This sorta sucks.

    The advantage is clear. the raw materials are more common currently. Also it future proofs your build. If you want to go to 5 lug down the road the rotors have the holes or you can get replacements off the shelf and just swap to 5 lug fox length axles and go. Saw a pic of one car that had 5 lug on one side, 4 lug on the other. Rims were "the same", tires were directional pattern. I guess that's one way to keep stupid from putting them on the wrong way... lol.

    Pondering the whole idea of SN95 rear brakes redone to 4 lug. Other than needing a drill press and patience, I'm not sure I see a clear disadvantage.

    Its an oddball combo in many ways if the front brakes are left completely 1986 stock but it seems to work. I initially ran my SN95 rearend with my 7/8" fox master cyl with an adjustable proportioning valve when I swapped in my SN95 rearend and used ranger rotors to go to 5 lug on my 86GT (before I redid my front end with SN95 parts). It seemed to work just fine. Stopped way better than stock, albeit nothing near how well it stops after a full on conversion.

  11. #11
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    Quote Originally Posted by erratic50 View Post
    Also it future proofs your build. If you want to go to 5 lug down the road the rotors have the holes or you can get replacements off the shelf and just swap to 5 lug fox length axles and go.
    On that same tip, '93 Cobra/T Bird rotors drilled for 5 lug are listed by Discbrakesrus in part of a kit.

    http://discbrakesrus.com/make/ford/r...gand5lug55.htm

    About 1/2 way down the page you'll see kits with those rotors. I don't see 5 lug '93 Cobra/T Bird rotors listed individually now but IIRC they did offer them by themselves at one point. Their site is kinda odd so they may still be there somewhere. If they'll sell 'em outside of the kit, at least it could be a "commercially available" option rather than straight custom.
    '85 GT

  12. #12
    FEP Super Member erratic50's Avatar
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    Great info - good to know there are options for going 5 lug with a Tbird setup down the road!!

    I stumbled across a thread talking about an approach to a 4 lug hub assembly for sn95 spindles last night too. Given the clear advantage of those spindles for Ackerman and sealed bearings, etc, I may start a discussion thread on that very topic just also for curiosity in what others have seen.

  13. #13

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    There were also 4-lug T-Birds (and Fox station wagons) that came with 10" rear drums, which work very
    well when combined with the later 11" front discs and good linings. For a low-buck solution, you can't
    get much easier (or cheaper) than that. My '85 Hatch has been running this combination for several
    years now, with Porterfield R4-S linings at all 4 corners. And given the choices, I'd do it again, unless
    maybe if I had wheels that showed off the fancy rear discs.

    But then, I'm very much the function over form type...
    Cheers,
    Jeff Cook

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  14. #14

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    So spend a ton of money for special, relatively rare tbird parts, throw most of it away, then use sn-95 stuff setup for 5 lug, convert it over to the special brake brackets for a tbird, then convert ot and everything in it to 4 lug.

    You could just start out with a mustang width axle. The brackets and length are what dictate where things set, not the rear end housing. If it were that much trouble, id just save the $$$ and go 5 lug.
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  15. #15
    FEP Super Member erratic50's Avatar
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    Quote Originally Posted by Haystack View Post
    So spend a ton of money for special, relatively rare tbird parts, throw most of it away, then use sn-95 stuff setup for 5 lug, convert it over to the special brake brackets for a tbird, then convert ot and everything in it to 4 lug.

    You could just start out with a mustang width axle. The brackets and length are what dictate where things set, not the rear end housing. If it were that much trouble, id just save the $$$ and go 5 lug.
    yep - thank heavens talk is cheap!

    Carefully plan once, use many.

  16. #16

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    The 94-98 mustang junk is all the same width as the stock tbird stuff as well. Makes a stupid easy 5 lug upgrade for us cougarbird guys. Even the turbo coupe guys go this way.
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  17. #17
    FEP Super Member erratic50's Avatar
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    My silver saleen build ended up with Northern Racing 4 lug conversion kit going on to a rebuilt 8.8. started with a housing I had laying around from my 1986GT

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