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  1. #1

    Default Rear Frame Rail Replacement

    I’ve been searching this forum all week and coming up with great information however any search with the words “frame” and “rail” only bring up the front frame rail posts. Has anyone here done a rear frame rail? If so do you have any info or tips on doing this job? I’ve found a few measurement posts which are helpful, but nothing specific to a rear frame rail such as shown in the link below. The car I purchased was sitting in a yard since 1995 in Maine so the majority of the floor pans and other pieces underneath suffered pretty severely. We’re looking at replacing the trunk floor pan, driver and passenger floor pans, front and rear frame rails, and torque boxes. (I’m sure there’s other things that will surprise us along the way)

    https://lmr.com/item/LRS-871R/87-93-...gaAkwwEALw_wcB

    Thank you

  2. #2
    Moderator wraithracing's Avatar
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    Default

    I have not replaced a frame rail on a Fox Mustang, but I have done some other cars. Its no different than most repairs in the sense that you measure twice and cut once. Better yet . . . measure 10 times and cut once. Based upon all you say needs repair work, I would recommend doing the repairs in an order that helps to prevent the unibody from tweaking due to those repairs, installing additional bracing and structure to tie everything together and hold during the repairs, or possibly have it done professionally depending on your skills and available tools.

    If you are like many of us, you can't afford to pay a shop to make the repairs as the car just isn't worth the cost of said repairs. With that, having the proper tools or at least having some quality tools and equipment to get the job done will make the whole process go better.

    If you were to cut all the rusty sections out at one time as mentioned above you are going to have a flimsy, floppy chunk of metal. You will have to brace the inside of the car to keep things straight and square relative to their original position. The downside is that structure can get in the way of working, without it and you have a greater chance of the whole car being tweaked when welded back together. Personally I would recommend buying the whole floor pan section from LMR or others rather than each side leaving the trans tunnel. The one piece will provide a better repair and be more OEM/Factory like than separate pans.

    Depending on the condition of the main structure where the torque boxes tie into, I would consider using that as a mid point. Make any repairs to that if needed, but try and keep that intact if possible and use that as a dividing line for the repair work. Then divide the work for areas forward of that area and behind that area. Although I do have to say, that for all the metal you need to replace a better donor body would be my first choice. You are going to spend at least $1K just in repair metal alone, if not closer to $2K and that doesn't include any labor. You might seriously consider trying to find a better body from one of the dryer states and have it shipped out. They are out there and can be found, just need to look. Good Luck and I am sure many of us will help all we can if you decide to make the repairs.
    Last edited by wraithracing; 11-17-2019 at 09:51 AM.
    ​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

  3. #3

    Default

    Trey thank you for the reply, and I agree we'll have to throw in bracing prior to ripping out the things that need to be replaced to retain the structural shape. This will be a pretty delicate job since the roof has ttops already.
    As for affording the body shop, I'd like to swing for a paint job but the fab work I plan on doing most myself (or friends).

    Thank you again Trey!

  4. #4
    Moderator wraithracing's Avatar
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    I completely understand the budget issues. That is the main reason why I know so much about paint and bodywork at this time. I couldn't afford to pay a body shop to work on my cars, but luckily one of my best friend's Dad was a paint and body man with 30 plus years of experience when I was in HS. So he helped get me started and things progressed from there. Hard to believe, but he is still working part time at the age of 80 years old as a body guy.

    I would recommend sorting out the back half of the car to begin with leaving the rockers and hopefully the main torque box structure intact while you make those repairs. If you can do that, then tackle the floor pan, I think you will be better off. You might also consider welding in SFC before cutting the floor out of the car. That will mean the new floor pan (if doing the whole pan which I recommend) will have to come in from the top, but that can add some stability and structure to the car to help keep everything square and true. Good Luck!
    ​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

  5. #5

    Default

    Trey just an update, I made some bracing and used the door bolts to connect them to the car. I then cross-braced them together and cut the factory brace out of the car last weekend:


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  6. #6
    Moderator wraithracing's Avatar
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    Looking Good!

    Nice progress and nice bracing. Very similar to what I build years ago when I put my first Four Eyed Fox on my Rotisserie.
    ​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

  7. #7

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    This month when I clean the garage out for more room I might look at making a rotisserie. I've read not to do structural changes to a vehicle while it's mounted so that'll be interesting with the rear rails and floor pan. I'm shopping around for some torque boxes as well so it should be a busy spring season.

  8. #8
    FEP Super Member gr79's Avatar
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    Default walking the line again

    Would be cool to mimic the factory line jig that traveled with the car body on it. Simple square flat chassis support for repair.
    Actual DAP line pictures help to plan reverse engineering for repairs.
    http://www.mustangandfords.com/featu...ne-in-michigan

    Will continue working the area at ps rear seat on my 79 this year.
    Have the same floor rust out over the frame rail at the front lower control arm bolt.
    Lots of rust chips were vacuumed out of the rail.
    The opening made it much easier working position to remove the 40 year old control arm bolt from the inside of car!
    Had to remove sheet metal there, about 1' x 1' square with snips. Rust made the metal thin underneath.
    Faced reality by poking metal with a large screwdriver confirming what had to go and what sounds to be ok.
    Side to side, from wheel well/seatbelt, to over the frame rail.
    Front to back, couple inches aft of the seat bottom bulkhead to where the floor pan starts curving up.
    Will make a thick removable metal plate there for future access and added pan to chassis box strength.
    Rocker overall is sound for the most part.

    When I replaced the ps lower control arm, added the p side parts of the NPD rear torque box reinforcement kit.
    https://www.npdlink.com/product/rein.../166458/151016
    Next will be sheet metal, plates, and repair of subframe at the rear bend up.

    Installed FRP M-5480-A cross braces and M-5478-B subframe connectors long ago and are working out fine.
    Instructions said to place jack stands under the rear axle tubes and front LCAs as close to the wheel as possible.
    Used floor jacks to hold the sfcs tight to the floorpan during install.

    Wonder how well these work:
    http://store.uscartool.com/mustang-7...connector.html

    Also have rear floor chassis reinforcement plates to add at the torque box areas.
    Were a part of Ford M-5024-A chassis stiffening kit. Same as installed in early vertis. E4ZX-76101A16-AA (RH) A17-AA (LH).
    They will be riveted per Ford instructions using included rivets (382707-S36, 1/4" x 5/8") in the kit. Factory did not weld these.

    Drivers side rear under seat area is ok. Seems the muffler kept that area heated and did not let dampness rust it out like the ps.

    Have used heavy gauge home deck framing angles to floor pan repairs at the firewall and rocker areas. Holding up fine.
    Hey a frame is a frame, no?
    Successfully replaced the rusted out front cab mounts on the radiator support on my Ranger, better than new, using deck brackets.
    https://www.fastenersplus.com/shop-b...framing-angles
    https://www.fastenersplus.com/shop-b...eel-connectors

    Using HF pneumatic rivet gun to set those big rivets quickly. Have gas mig welder, but no garage shelter limits outside repair windows.

  9. #9
    FEP Super Member gr79's Avatar
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    Anything goes at this house as to ideas for repair with off the shelf parts.
    Bought one of these a while ago. Something to hold and study how i can use it.
    https://www.lowes.com/pd/edsal-1-Pac...rdware/4222543

    Measured it.
    .050" thick metal. about 18 gauge, black powdercoated or something similar.
    1/2" wide flanges
    2.5" max width at flanges outer edges
    1 7/8" inner box width and depth
    2" depth outside box under flange to bottom

    A genuine off the shelf part. Part of a shelf itself.
    Bulk storage rack shelf cross brace for pallet support.
    Designed to hold weight, 1000# a common spec. Inexpensive
    Items remembered from my material handling days stocking racks.
    https://rackandshelf.com/product/sto...llet-supports/

    Top hat style, roll in, similar shape as rear frame rail. U channel, hat channel roll formed metal.
    Ha Edsal brand. Edsel with an e is the car.
    https://www.google.com/search?q=hat+...w=1152&bih=693

    Now to measure the rear frame channels on the car.
    Thinking of as a short slip in/on rail patch or doubler. Mod to fit.

    Read floor pans are 16-18 gauge metal. Stamped ribbing adds strength over a plain flat sheet.

  10. #10

    Default

    I've done PLENTY of front frame rails. Last one I did I replaced the entire front unibody. Set the car up how you need it and spend an hour or two measuring and making a diagram It saved me a TON of time while I was reinstalling. I slid the entire front unibody out prepped the new one and slid it in. Measured and welded. I've also replaced just one side and or core support. same thing measure measure. Rears are a little tougher but once the floor is out it will get easier. I did just section an entire rear frame trunk floor and inner wheel house on a SN95. What a PITA. Those cars get 100 times rustier than foxes. IDK what Ford did or didn't do but those cars RUST.
    Attached Images Attached Images     
    Last edited by PaceCar79; 03-07-2020 at 09:42 AM.
    Chris,
    You guys go ahead and restore em! I'm gonna mod em!

    79 Pace Car, 96K Original, Turbo 4, 4 speed. Soon to be V8 5 Speed!
    83 GT Project
    79 Z28 89K Original!

  11. #11

    Default

    Chris I wish I lived closer to you. I’d just loiter in your shop and pass you a cold drink every now and then while taking notes.

  12. #12

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    Quote Originally Posted by JustinL View Post
    Chris I wish I lived closer to you. I’d just loiter in your shop and pass you a cold drink every now and then while taking notes.
    Thanks LOL. Never a dull moment around here. One gets done another starts...
    My son is in LOVE with his now done new SN95.
    Hard to believe 6 months ago this was a wrecked rusted V6 auto pile of mess.
    Attached Images Attached Images    
    Last edited by PaceCar79; 03-09-2020 at 08:47 AM.
    Chris,
    You guys go ahead and restore em! I'm gonna mod em!

    79 Pace Car, 96K Original, Turbo 4, 4 speed. Soon to be V8 5 Speed!
    83 GT Project
    79 Z28 89K Original!

  13. #13
    FEP Senior Member Tigger's Avatar
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    Nice work. I wish I had your body skills.
    67 Mustang Coupe
    96 Tangerine GT
    86 Saleen #179

  14. #14
    FEP Senior Member
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    Default

    JustinL, do you have the parts needed to replace the rusted out parts? I have an 83 shell that has no rust or damage from the rear seats to the bumper. Both of the outer quarter panels are damaged but all of the interior metal is fine. The whole rear frame is in great shape. If you are interested in that whole back end of the car, I can sell it pretty cheap. I hate to send it to a junk yard. I'm located in Pa by Erie. I see you live in CT. PM me if your interested. I bought the shell for the T-top parts. Don't need the rest.

  15. #15

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    Quote Originally Posted by dynodon64 View Post
    JustinL, do you have the parts needed to replace the rusted out parts? I have an 83 shell that has no rust or damage from the rear seats to the bumper. Both of the outer quarter panels are damaged but all of the interior metal is fine. The whole rear frame is in great shape. If you are interested in that whole back end of the car, I can sell it pretty cheap. I hate to send it to a junk yard. I'm located in Pa by Erie. I see you live in CT. PM me if your interested. I bought the shell for the T-top parts. Don't need the rest.
    I appreciate that offer but Lake City is a 8hr trip for me in CT. I may have a roller lined up for $500 (no motor/trans) that I can grab the things I need, just have to find a storage unit to hide it from the wife.

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