Drivetrain Picked Up A 04 Irs For My Fox, Have Some Questions.

Discussion in 'Fox 5.0 Mustang Tech' started by bird_dog0347, Jul 11, 2013.


  1. bird_dog0347

    bird_dog0347 Active Member

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    First off, the end goal of the car is a great street/twisty road handling weekend cruiser that will likely never see a drag strip nor will it be a full blown race car. I'm just trying to get all the suspension, brakes, chassis work squared away before I add any more power to it. I don't mind some level of increased NVH but I'm not building a full blown race car so I'll sacrifice some performance to keep it streetable.

    The front suspension has been totally redone with Blue Tokico struts, 95 spindles, 13in Cobra brakes, polyurethane control arm bushings, poly sway links and bushings, MM Solid steering rack bushings, MAC C/C plates, Eibach Sportlines, and Moog ball joints.

    It's a pretty stock 5.0 right now with just an explorer intake, under drives, long tubes & off road H, and a cat back. It still has stock heads, I'm not sure about the cam but if it isn't stock it's pretty mild.

    Given that info, I'd guess I'm not putting more than 225 HP to the wheels... So I'm wondering if I can just bolt up the IRS as is till I can afford all the proper derilin/poly (no aluminum, it's a street car first and foremost) bushings and not worry about breaking anything in the rear end with the little power I'm making at the moment. It'll be next spring or so before I can afford to do it right with the bushings and I won't necessarily mind having to pull it back off to work on it then.

    I only had to pay $500 for the whole thing, complete with everything minus the Cobra rear calipers, but I did get the brackets for the calipers as well as the rotors. It also has a rear diff brace on it, came with IRS tail pipes (which wont work with my current cat back so I'll at least need new mufflers), Bilstien shocks, and stock springs. My current stick axle is a SN95 disc rear and I have a few questions about the swap. I was wanting at a minimum to add gears (3.55) and a panhard bar to the SRA so this seemed like a better way to spend the money.

    1. Can I keep my rear SN95 V8 calipers and use them in the cobra rear caliper brackets or do I need the cobra calipers too?
    2. I'm currently running sportline springs but the SRA springs won't work with the IRS lower spring cups. Can I cut the stock springs for now to even out the ride height till I can buy a coilover kit for the rear or at least the proper rear springs? If I do cut the stock ones, how much can I expect the handling to suffer?
    3. I just bought the e-brake cables but haven't installed them yet for the disc rear conversion on the fox, I assume they will work on either the GT or the Cobra rear calipers once I get the IRS installed?

    I'm sure I'll have more questions but that oughta get me started.

    The car it's going on:
    [​IMG]

    The rear end:
    [​IMG]
    #1
  2. MFE92

    MFE92 Active Member

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    No. The IRS requires far stiffer springs than the stick axle, and simply cutting the stockers won't get it done.
    #2
  3. bird_dog0347

    bird_dog0347 Active Member

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    To be clear, I'm talking about the stock IRS springs, not the stock SRA springs. Same answer?
    #3
  4. MFE92

    MFE92 Active Member

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    No, in that case you can probably trim them
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  5. reldla1996

    reldla1996 Member

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    For bushings, go to Full Tilt Boogie Racing. They specialize in the Cobra IRS, and have the best bushings you can buy. They talk about increased NVH with the aluminum front mount "bushings", and I was worried about it, but honestly the increase in NVH was minimal. With what you've done to your front end, you won't mind it all, as long as the gears are properly set up.
    #5
  6. bird_dog0347

    bird_dog0347 Active Member

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    I've been aware of and checking out their stuff for a while now. It's on the list, just not in the budget right now.
    #6
  7. Mustang5L5

    Mustang5L5 Car used in adult film "Highway Gangbang-InDaButt" SN Certified Technician Founding Member

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    The calipers themselves are the same, but the mounting brackets are different. You didn't clarify which brackets you had. Are they the u-shaped pad support brackets, or the brackets bolting to the rear axle?

    You can buy the pad support brackets separate and swap them out. The difference is the slot the rotor rides in is wider for the wider cobra rotor.

    Actual calipers that squeeze the pads are the same. Ebrake cables i beleive will work as well
    #7
  8. bird_dog0347

    bird_dog0347 Active Member

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    I got the caliper mounts that came with the IRS, they are the cobra caliper mounts. So since the calipers themselves are the same, now I just have to worry about the soft lines since I didn't get those. I need to see if the soft lines currently on my calipers will work on the IRS, but I'm not sure they'll be long enough.
    #8
  9. Mustang5L5

    Mustang5L5 Car used in adult film "Highway Gangbang-InDaButt" SN Certified Technician Founding Member

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    They won't be. You'll need to research here what other fox Mustang owners do.

    The cobra uses 4-channel ABS, so the two rear brakes run a separate line from the MC back and the lines run on each side of the body. The fox, as we know, has only a single brake line to the rear in the trans tunnel.

    So you will need to split the line and then run two addional brake lines along the body and then mount the 99-04 Cobra rear soft lines.
    #9
  10. bird_dog0347

    bird_dog0347 Active Member

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    Yeah, I've already done the research... I know I have to fab up a T fitting and two hard lines to split to the wheel wells... I didn't get the Cobra rear soft lines that connect the calipers to the hard lines I have to run so I'll either need to buy those or see if my soft lines that connect my calipers to the hard lines on the SRA are long enough to fit (I'm with you and doubt they will be).
    #10
  11. RacEoHolic330

    RacEoHolic330 I like to dress like a pretty girl SN Certified Technician

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    I have Stifflers braided lines for my IRS and they are easily twice as long as the soft lines when I had my solid rear.
    #11
  12. bird_dog0347

    bird_dog0347 Active Member

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    Any chance you can provide better pics of the hose connections? What ends are on the custom hard lines you ran to the wheel wells in order to connect the stifflers lines to the hard lines? The lines I see on their site look to connect only to the hard lines from the Cobra???

    http://buystifflers.com/StainlessSteelBrakeHoseKitMustangCobra9904Rear-1-1.aspx
    #12
  13. RacEoHolic330

    RacEoHolic330 I like to dress like a pretty girl SN Certified Technician

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    Check out my build thread. I posted a few more pictures there. The connections are not done yet though. I forgot to get adapter fittings. Here are all the parts you'll need to make it work:

    WH 1442 - M10x1.0 to 3/8-24 adapters (to connect hard lines to soft lines - two needed)
    WH 702X3 - Three way 3/8-24 Tee fitting
    BK 8131204 - 20" pre-fabbed 3/16" hard line with 3/8-24 fittings
    BK 8131205 - 30" pre-fabbed 3/16" hard line with 3/8-24 fittings

    The part numbers are from Napa. The adapters might be special order. My local Napa has to order them for me.
    #13
  14. bird_dog0347

    bird_dog0347 Active Member

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    Thanks man, I saw the pics and I really appreciate the list.
    #14
  15. David Pepiton

    David Pepiton Active Member

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    the calipers are the same for the GT and the SVT cars. however if i remember right the left caliper would have to be used on the right side and the right on the left to get the EBC on the correct side. the GT caipers were slightly cheaper then the cobra calipers even though they are the same just switched. im not sure it will need to be that way with the irs though.
    #15
  16. RacEoHolic330

    RacEoHolic330 I like to dress like a pretty girl SN Certified Technician

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    Bah. Ignore this post.
    #16
  17. bird_dog0347

    bird_dog0347 Active Member

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    Good deal...

    I found out today that Amazon was selling some of the prothane bushings for the IRS REALLY cheap, so cheap that even though I plan to buy and install FTBR stuff next spring I went ahead and spent the $30 to get the subframe mount poly bushings as well as the diff mount (front and rear) poly bushings. I know this won't be a long term solution but I figure it's better than the rubber ones in there for now and for $30 it was worth it.

    Prothane 6-1609 Red Front IRS Differential Bushing Kit
    Automotive
    Sold by Amazon.com LLC
    $13.61
    Prothane 6-1610 Red Rear IRS Differential Bushing Kit
    Automotive
    Sold by Amazon.com LLC
    $5.39
    Prothane 6-111-BL Black IRS Subframe Bushing Kit
    Automotive
    Sold by Amazon.com LLC
    $9.82
    #17
  18. betke76

    betke76 Member

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    interested in this swap, looking forward to hearing your input on the difference in handling, if you think it was worth it
    #18
  19. David Pepiton

    David Pepiton Active Member

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    yeah I'm very interested because I have a customer with one for sale for $350 with poly bushings already installed. hes going to solid axle since hes planning on making over the 800whp mark hes looking to swap in a 9 inch I have so if we swap it will only be $100.
    #19
  20. bird_dog0347

    bird_dog0347 Active Member

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    So I got my IRS all disassembled and I'll be cleaning it up completely, making it look new before it gets installed. One of the main reasons for taking it apart right now was simply to get the subframe mounted up without all the additional weight as I'll likely be doing it myself. Also I ordered the aforementioned bushing kits so it'll be easier to install them with it all apart. As it currently sits in my garage...

    As you can see, it's very dirty but I'm going to clean it and paint it to make it new again.

    [​IMG]

    [​IMG]
    #20

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