Engine cross member frame rail nut - Vintage Mustang Forums
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post #1 of 24 (permalink) Old 07-26-2019, 02:00 PM Thread Starter
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Engine cross member frame rail nut

Plugging along with my re-assembly after welding and body work on my 64.5 vert. New front frame rail put in on passenger side. Driver side not replaced by the shop. Went to install crossmember and where there should be a nut on the driver side, i have a big hole. Ugh! I guess when the shop removed the crossmember, they must have ripped out the nuff because the crossmember was in place when i delivered them the car.

I saw a thread saying that it can be replace with a riv-nut. I researched the 1/2-13 riv nuts and the dimension across the flats is about “.625. THe hole in my frame rail actually is hex shaped (probably from shape of the nut), but is .850” across the flats. Riv nut wont work. Photo attached of hole where nut was.

Does anyone have any photos of what the original looked like? I’d appreciate anything but a section of what the rail originally looked like on the inside would be great.

Any advice on how to repair would be greatly appreciated. I can turn wrenches, but i am not a welder. Looks like the care will be flat bedded back to the shop. I want to be able to give them direction on how to repair if i do need to bring it back to them.
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post #2 of 24 (permalink) Old 07-26-2019, 02:32 PM
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Easy repair...grind away the paint, thread a bolt into the nut to prevent the threads warping while welding...and weld the nut into place around the perimeter. Just have to find an original style nut(or not if you dont care). Any shop with a welder would be able to do it for you...from an exhaust shop to a friend you know, not sure I would take it back to the same place that broke it to begin with though.

Last edited by wicked93gs; 07-26-2019 at 02:34 PM.
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post #3 of 24 (permalink) Old 07-26-2019, 02:35 PM
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You can have a nut welded in or you can use a spacer block, carriage bolt and fish wire. This link shows the spacer block and there is a video on the page that shows how it is used with the carriage bolt and fish wire.


https://www.etrailer.com/Accessories...se/RP3022.html


I provide this hardware with my Falcon lower engine cross members so that Falcon owners can install a traditional Boss 302 style crossmember on a Falcon which did not have cross members. I supply a 1-1/8" hole saw also so they can drill the necessary size hole in the bottom of the frame rail to fish the spacer block and carriage bolt into the frame. This technique is used for trailer hitches on vehicles that have existing holes in the frame rail or for custom jobs that require a hole to be drilled into the frame rail. Don't worry about drilling a hole in the frame...there already is a hole there as you well know for the swaged crossmember nut. This technique actually helps to restrengthen the hole area (even though it is not an issue) because the entire assembly has a clamping force when you tighten the carriage bolt nut.

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post #4 of 24 (permalink) Old 07-26-2019, 05:34 PM
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Originally Posted by wicked93gs View Post
Easy repair...grind away the paint, thread a bolt into the nut to prevent the threads warping while welding...and weld the nut into place around the perimeter.
Not helpful as you may not grasp the issue here. The nut necessarily needs to be anchored securely inside the frame rail so the brace can sit flush on the outside. Due to the dynamic forces the brace is designed to resist and the special shaped bolts required this isn't something you can just weld a nut on the surface of.
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post #5 of 24 (permalink) Old 07-26-2019, 07:39 PM
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Putting a carriage bolt inside the frame is not gonna do it. You must have a hardened nut inside, to accept the unique tapered seat bolt used for these crossmembers. A nutsert won't do it either, not strong enough. Now, that plate would be useful if you welded a nut to it, and slipped it inside the frame, then welded the plate in place centered on the crossmember hole using a 1/2" hole on each side of the bolt hole.


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post #6 of 24 (permalink) Old 07-26-2019, 11:39 PM
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Quote:
Originally Posted by 4ocious View Post
Not helpful as you may not grasp the issue here. The nut necessarily needs to be anchored securely inside the frame rail so the brace can sit flush on the outside. Due to the dynamic forces the brace is designed to resist and the special shaped bolts required this isn't something you can just weld a nut on the surface of.
I wasn't suggesting welding a nut on the surface. There is a nut shaped hole...obviously the nut sat flush(as they always do) and the weld holding it broke loose. put a nut back in the nut shaped hole(flush of course) and weld the perimeter of the nut to the frame rail...just like it was before the(obviously inadequate) previous weld broke loose, then grind the surface flush again. If you were really worried about it beyond that, you could cut open the side of the frame rail, slide in a block of metal the width of the inside of the frame rail and an inch thick...weld it to the inside of the frame rail, close the frame rail back up and weld it(also to the metal block)...then drill and tap that 1" block for the thread of the crossmember bolt. There are any number of potential fixes...some as weak as the factory solution, and some much stronger...but I wouldnt trust any that didnt require welding. A carriage bolt through the top of the frame rail may well work...but would be susceptible to potential wallowing of one or the other hole if there is any force applied to the bolt.
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post #7 of 24 (permalink) Old 07-27-2019, 05:40 AM
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Originally Posted by wicked93gs View Post
I wasn't suggesting welding a nut on the surface. There is a nut shaped hole...obviously the nut sat flush(as they always do) and the weld holding it broke loose. put a nut back in the nut shaped hole(flush of course) and weld the perimeter of the nut to the frame rail...just like it was before the(obviously inadequate) previous weld broke loose, then grind the surface flush again.
Again not helpful. The nut must necessarily be inside the frame rail, and flush with the edges of it would likely not allow the tapered bolt to seat properly and allow the brace to be tightened to spec. I don't recall that torque specification offhand but I'm sure zray (our resident expert) knows it by heart, and it's considerable. But even if the tapered bolt did seat all the way, your method could not possibly leave enough strength of material behind to be trusted after grinding it down for the brace to sit flush as it must. Also, the original factory nut welds inside the frame were not to keep the nut from pulling out, they were to keep the nut from moving laterally in any direction. Your method would leave only the thinnest of connections around the perimeter of the nut and in no possible way strong enough. It would break and pull out. I don't believe you comprehend the dynamic forces involved in this most critical of connections. Were that nut to pull out in a turn at speed (the most likely scenario of extreme stress) it would cause the car to leap up and sideways so abruptly the best driver that ever lived could only look to see what they were about to hit.
No welding shop worth it's insurance policies would do this repair that way.
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post #8 of 24 (permalink) Old 07-27-2019, 07:41 AM
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I guess its a little different than say the infamous front bumper frame rail nuts breaking loose but still...You really don't think if you egged the hole out a little and stuck a nut on a bolt in there and welded it in it wouldn't hold? How about if the op did that and added a Zray cross member which has a bolt going thru it from the lower control arm? I would think that strong enough, and you get that sweet jackpadded xmember to boot! I have never had to deal with this, but many others have, curious if those repairs held up and how they were done. If the op wants to stay with the so so stock cross member, maybe if you welded a new nut into a piece of pipe, then cut the old hole to the larger pipe diameter and welded that in there...I would think that as strong as the factory set up. Is welding a nut to a plate, cutting open the rail and sticking it in there and welding it in, then welding the access hole back up really necessary on a street car? That's a lot more work for sure... I went to blkfords trailer site but could not find the video., but I get the idea..maybe some more folks will chime in!!
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post #9 of 24 (permalink) Old 07-27-2019, 08:29 AM
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I would take it back to the body shop and make it their problem, the job you paid them for is not complete. They should be able to fix it correctly. You should be able to look at the other side and see what should be there and make sure you inspect their work to make sure it's done right. BTW, this is a good time to add an aftermarket cross member that picks up the Lower Control Arms tightening up your suspension.


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post #10 of 24 (permalink) Old 07-27-2019, 08:56 AM
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I had to replace both front sections of my frame rails. I also had a crossmember nut that had been twisted off many years ago, a previous owner welded that side of the crossmember to the frame rail. Since I had both sides opened up I welded 2 new grade 8 nuts on the inside. It's not a difficult repair, the difficulty will be in trying to find someone willing to do it. Most shops don't want nothing to do with old cars. Try talking to some guys in your local classic car club. Almost guarantee they will know someone who would fix it for you. Best way to fix it is to drill out some spot welds, then use a thin cutoff disc to neatly remove a section just long enough to make the repair. Fetch the old nut, remove the rust around the hole, weld in a new nut, then weld your section back in.

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post #11 of 24 (permalink) Old 07-27-2019, 08:57 AM
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Shops charge for rusted/seized/stripped bolts...yes. they should have told you it happened and by the way, that will be x dollars to fix it and we recommend doing it such and such a way..I also agree on the upgraded cross member even for a street car. Great place for tow straps when trailering it and with the jack pad, a good point for using your floor jack.
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post #12 of 24 (permalink) Old 07-27-2019, 11:08 AM
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Quote:
Originally Posted by 4ocious View Post
Again not helpful. The nut must necessarily be inside the frame rail, and flush with the edges of it would likely not allow the tapered bolt to seat properly and allow the brace to be tightened to spec. I don't recall that torque specification offhand but I'm sure zray (our resident expert) knows it by heart, and it's considerable. But even if the tapered bolt did seat all the way, your method could not possibly leave enough strength of material behind to be trusted after grinding it down for the brace to sit flush as it must. Also, the original factory nut welds inside the frame were not to keep the nut from pulling out, they were to keep the nut from moving laterally in any direction. Your method would leave only the thinnest of connections around the perimeter of the nut and in no possible way strong enough. It would break and pull out. I don't believe you comprehend the dynamic forces involved in this most critical of connections. Were that nut to pull out in a turn at speed (the most likely scenario of extreme stress) it would cause the car to leap up and sideways so abruptly the best driver that ever lived could only look to see what they were about to hit.
No welding shop worth it's insurance policies would do this repair that way.
Ah, this nut must have a built in shoulder on the back side then...you could still use the method I described and get enough bead on the back side of the sheet metal frame rail easily enough(its pretty easy to push a bead right through sheet metal as if it wasn't even there). But that leaves opening up the frame rail as the best method for repair so you can actually see whats going on. The drilled/tapped/welded in metal block is still going to be the strongest method though...a fix like that would never break again(or pull out for that matter)
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post #13 of 24 (permalink) Old 07-30-2019, 03:03 PM
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Another solution

Worked on a 65 convertible

I'm reluctant to cut the frame rail at that critical juncture of LCA, cross member and shock tower. But I was able to find a way to replace the captive nut w/o cutting a section out of the frame rail. Using thin MIG wire I was able to fish a plate/welded nut assembly over the existing hole in the frame rail and tack weld it in place.

1) Fish a MIG guide wire starting thru an opening at the very front bottom of the frame rail thru to the hole where the captive nut should be.

2) Fish another guide wire thru an opening in the frame rail towards the rear of the car that looks like a hex head fastener thru to the hole where the captive nut once was. Twist the 2 guide wires together. Now you have a guide wire from the front of the car passing over the captive nut hole in the frame rail.

3) Drill a 5/8” hole approx. 1˝” from the end of a 1 1/2” x 4” steel plate . Center a grade 8 nut over this hole and weld to the plate. Drill a small hole in each end of the plate to attach guide wires. The steel plate needs to be long enough not to rotate inside the frame rail, it must extend beyond the cross member for welding, and be just wide enough to fit through the access hole in the frame rail.

4) Enlarge the opening in the front of the frame rail enough for the plate/nut assembly to fit thru.

5) Tie the plate assembly to the guide wire at the long end of the plate. Tie a chase wire to the short end of the plate assembly to help maneuver it.

6) Pull the nut assembly thru the frame rail (long end first, flat end facing down), center it over the captive nut hole and install both bolts through the cross member to ensure the spacing is correct.

7) Approximate where the long end of the assembled plate is within the frame rail and drill a small hole thru the frame rail and thru the steel plate. Weld the plate to the frame rail using this hole.

This worked using the driver’s side frame rail and would probably apply to the passenger side as well.
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File Type: png Plate_nut asm.png (124.6 KB, 82 views)
File Type: png Rear guide hole.png (116.8 KB, 80 views)
File Type: png Front guide hole.png (123.1 KB, 80 views)
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post #14 of 24 (permalink) Old 07-30-2019, 03:15 PM
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A standard 1/2-13 steel nut is 3/4 inch across the flats. Simply grab one and insert through your hole....use a long 1/2 inch bolt and gravity to hold it in place... turn it so the crown of the hex is sitting on the flat of the frame rail... then tack it in place, remove the bolt then finish welding it in place.

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post #15 of 24 (permalink) Old 07-31-2019, 06:31 AM
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Grade 8 nut too large

Maybe a std grade nut is acceptable, but since the mounting bolts are grade 8 I thought it best to go with a grade 8 nut. The problem was that the grade 8 nut is too big to fit thru the hole in frame rail and I didn't want to grind it down or cut on the frame rail.
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