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  1. #1
    FEP Member
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    Default PLEASE HELP with Double hump cross member

    If I find a double hump crossmember will it be a direct bolt in for my 79 pace car ?? I'm trying to install dual ex & wondered IF the double hump X-member will help install dual ex with long tube headers?? Just not sure whats required to install in a 79..Surely someone has done this??ANY help greatly appreciated.. Thanks

  2. #2

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    Its not a direct bolt in. You have to cut the tubes down so it will fit in between the brackets. Is your car auto or stick? If it is stick to you have a T5 or SROD?
    '79 Indy pace car T-top
    '81 Cobra
    '81 Cobra T-top
    '82 Mustang GT T-top
    '87 Corvette
    '10 Mustang GT Convertible
    '17 F250
    '17 Landrover Discovery Sport

  3. #3
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    Greg- THANKS that was Fastt ! Ok, You say you have to cut the tubes down to fit between the brackets ?? Do U mean the tubes on the crossmember where bushing goes thru. How much trimming is required ? My car is std 4-speed, However t-5 sits awaiting parts to complete that project..

  4. #4
    FEP Super Member eric5oh's Avatar
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    Default

    Or relocate the bracket on the floor pan.
    2017 Lincoln MKZ AWD
    2003 Town Car
    2017 GTI
    Currently Foxless

  5. #5

    Default

    Yes the tubes where the bushings go through. You have to cut them so they are almost flush with the crossmember itself. When you get under the car you will see what I am talking about.

    You can also weld in some different brackets from a newer mustang.

    I think the T5 mounts back further so you may need to modify the brackets. I remember the SROD fit the crossmember OK but I am pretty sure that the T5 mounts back further.
    '79 Indy pace car T-top
    '81 Cobra
    '81 Cobra T-top
    '82 Mustang GT T-top
    '87 Corvette
    '10 Mustang GT Convertible
    '17 F250
    '17 Landrover Discovery Sport

  6. #6

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    Yes, the tubes / bushings must be cut to fit between the brackets. I have done this on my '79......the t-5 will mount correctly to the cross member when this is done. It is worth the effort.
    1979 Mercury Capri RS 5.0

  7. #7

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    will this mod have to be done on an 1984 lx 5.0 with single exhuat, i am ready to do this exhaust change over myself with all factory header/factory 4-cat H-pipe and a flowmaster cat-back.? please lmk. thanks.

    Ernesto

  8. #8

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    I would not mess with the brackets on the bottom of the car. Just modify the double hump crossmember as follows:

    1. Remove the 4 rubber bushings from both ends of the outer mounting tubes.

    2. On each side there is an 'inner' steel tube that mounts inside and is supported by each bushing. Remove the inner tubes (2) from the bushings. (They may be rusty and you may want to clean them up a bit with a whire wheel, etc)

    3. Using a fine tooth hacksaw cut the outer mounting tubes off flush with the sides of the crossmember stamping.

    4. Re-install the 4 rubber bushings leaving the inner tubes out for now.

    5. With the outer tubes cut off flush and the bushings re-installed measure the distance across the modified crossmember from the outside of one bushing to the outside of the opposite bushing - note this dimension - it should be the same as the distance between the brackets on the bottom of your car (2.75 inches).

    6. Cut the inner tubes to this length, remove the bushings and install the inner tubes and bushings in the outer tubes.

    If you are concerned about cutting too much, etc, you can take some measurements first:

    1. The distance between the brackets on the bottom of your car should be 2.75 (2-3/4) inches.

    2. The width of the crossmember without the extending tubes (as if cut off flush) on each side should be 2.25 (2-1/4) inches (measure before cutting).

    3. The length of the rubber bushing extending beyond the tube on each side should be .25 (1/4) inch.

    4. The modified crossmember would then be 2.25 +.25 + .25 = 2.75 wide., same as mounting brackets.

    Ford changed the undercar mounting bracket dimension on Fox Mustangs from 2.75 to 4.50 inches starting in 1982, so 1982 and later Mustangs do not require any mods to the car or double hump unit to install it.

    According to FMS catalog:
    Fox cars with 2.75 brackets:
    78-81 F/Z
    79-81 Mustang
    81-82 G/C

    Fox cars with 4.50 brackets:
    82 -83 F/Z
    82-up Mustang
    83 - up L/M
    80-88 T-Bird

    Good luck,
    Paul

    Please click here to check out my 78 Zephyr at my crappy Cardomain webpage
    1978 Mercury Zephyr 4-dr / Holley 600 vac sec carbed 1989 5.0L HO with Edelbrock Performer intake / MSD-6A / T-5 / 8.8" rear 3.27:1 / Mustang 5.0L brakes, suspension, steering / Dual exhaust / Mustang 10 hole wheels / P225/60R15 Goodyear Eagle TR

  9. #9
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    Paul- Sounds really simple.. THANKS. Why couldnt a person remove tubes & cut extra from center then reinstall everything?? That way we would still have the lips on outer end of tubes.. I believe these lips are to serve as a stop for bushings?? THANKS ALL

  10. #10

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    Quote Originally Posted by pace car 1320
    Paul- Sounds really simple.. THANKS. Why couldnt a person remove tubes & cut extra from center then reinstall everything?? That way we would still have the lips on outer end of tubes.. I believe these lips are to serve as a stop for bushings?? THANKS ALL
    If I understand you correctly what you are considering would require carefully grinding off all the spot welds that hold the tubes on, cutting the tubes in half, removing tube length(from now 4 pieces of tube) and welding them all back in. And all this work to save the little lips/flairs on the ends of the tubes, right? Thats a lot of work and in my opinion a PITA.

    When you cut the tubes off flush with the crossmember the stamping itself will act as the 'stops' for the bushings. The bushings have two diameters - the smaller one fits inside the tube and a larger one that prevents the bushing from going into the tube too far. This larger diameter prtion of the bushing will rest against the crossmember stamping once modified. I've run my Zephyr this way for almost 7 years with NO PROBLEMS.

    Paul
    1978 Mercury Zephyr 4-dr / Holley 600 vac sec carbed 1989 5.0L HO with Edelbrock Performer intake / MSD-6A / T-5 / 8.8" rear 3.27:1 / Mustang 5.0L brakes, suspension, steering / Dual exhaust / Mustang 10 hole wheels / P225/60R15 Goodyear Eagle TR

  11. #11
    Travis T
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    Quote Originally Posted by The LX Kid 5.0
    will this mod have to be done on an 1984 lx 5.0 with single exhuat, i am ready to do this exhaust change over myself with all factory header/factory 4-cat H-pipe and a flowmaster cat-back.? please lmk. thanks.

    Ernesto
    No, it is a direct fit on an 84 (I have done this to my 84). Only the 79 and I think 80 cars have to have the crossmember or floor brackets modified. I think it changed in 81, and stayed the same from that point on.

  12. #12

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    Quote Originally Posted by Travis T
    Quote Originally Posted by The LX Kid 5.0
    will this mod have to be done on an 1984 lx 5.0 with single exhuat, i am ready to do this exhaust change over myself with all factory header/factory 4-cat H-pipe and a flowmaster cat-back.? please lmk. thanks.

    Ernesto
    No, it is a direct fit on an 84 (I have done this to my 84). Only the 79 and I think 80 cars have to have the crossmember or floor brackets modified. I think it changed in 81, and stayed the same from that point on.
    coolness! thats a relife! thanks.

    Ernesto

  13. #13

    Default double hump

    We have an 81 t-top coupe and it is not a direct bolt on. I think Ford changed that in 83.
    84 GT Turbo T-Top
    78 F-150 4X4 W/ 38.5's
    Lots of other junk.

  14. #14
    Venomous Moderator Hissing Cobra's Avatar
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    I discovered this post a little late but here goes. On my '79 Cobra, I had to shorten the tubes and have them rewelded. Also, because I installed a Tremec 3550, I had to drill out all of the spot welds on the floor brackets and move them to their new location before rewelding those. I then had all holes in the floor rewelded before painting.
    Pete Slaney

    1979 Mustang Cobra

    347/T-5/4.30's
    420 rwhp/380 rwt (New Motor)
    11.49 @ 121.86

    306/T-5/4.30's (Old Motor)
    307 rwhp/278 rwt
    12.38 @ 111.38

  15. #15
    Mike Croke
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    I had the same issues on my '79. When I put the car together with the T-5, I used the x-member from my '86. To make it work, I cut the ends off the '79 x-member and welded them to the the '86. Once I got the TKO, I had to further modify it by notching the leading edge for clearance and adding the tab to the back for the transmission mount.




  16. #16

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    So if I have an '80 and have already moved the cross member back on the tubes for a tko, I need to move the rear tab on the frame back?
    Or in other words is the front tab in the same spot as the front tab on the newer vehicles?

  17. #17
    FEP Member toaster's Avatar
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    Default

    Great info for all. I was wondering about the transmission hangers. There seems to be a hanger for manual transmissions but do automatics need one too? According to latemodelrestoration.com the manual bolts between the tail and the mount to hang the h-pipe. I have a 1979 Cobra with a C-4 transmission (I believe). Would I need a hanger at that point?

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