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Discussion Starter #1
Since I have the rear end out of my car for a refresh, I decided to clean off some of the undercoat with brake cleaner. I noticed a small tear on the passenger side upper control arm torque box and it's probably been there for 20 years.

I do have a panhard bar now, so perhaps it will take some of the stress away from this mount? I'm wondering if I should be concerned and try to fix it. I don't have a welder, so I'd have to fabricate some kind of bolt through plate to keep it from spreading. At least I can clean it up the bit and maybe drill a hole at the end to stop it from spreading further, unless that only works for concrete? What do you guys think?
torquebox1.jpg
torquebox2.jpg
 

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Doesn't seem too bad but.....Seems like a good time to go the torque arm route,the wife might even buy that excuse.
 

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Stop drilling cracks is somewhat common in our industry. Could be anywhere from .125 to .250 diameter depending on where. Sometimes cracks are slotted, to avoid other cracks from propagating from the original crack. You can also drive a pin/rivet/hilite into the stop drill hole to support the crack in shear loads.

You learn some interesting stuff talking with structure engineers while working aviation lol.

I’d stop drill it for now and see what happens. Would be a good time to smooth out the edges of the torque boxes to eliminate and future cracks from forming. You want nice smooth radii without sharp apexes.
 

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If there are tears in that mount, then some of the spot welds are already torn through. Most of the spot welds are to the crossmember beam running between the frame rails. Because you can't see the top of this beam, it is very difficult to finds the torn spot welds. Some of the spot welds are directly to the bottom of the floorpan. You can pull the back seat out of the car and look down on the floor. There will be little circles where the spot welds are. If they are torn, there will be a little ring with a gap all the way around it.

You can find which spot welds are torn from the bottom with a mirror and flashlight, but this is very difficult to do. You have to hold the mirror up at a 45 degree angle and use the flashlight to look between the pieces of metal where there is a spot weld, to see if there is a gap between them.

If you don't fix this really soon, the damage will cascade very quickly. You need to drop the rear axle housing out of the car so that you can get good access. Clear out the metal between the UCA mounts and floorpan really well. Sand the edges to remove the paint. Then start stitch welding the joints between the parts. 50% on/50% off. This will stop the tearing.
 

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Get some wire wheels, strip the paint and rust. If you want to be sure, get a dye penetrant kit ($200) to spray to see where the crack actually ends. Use the end of the crack as the center mark for the drill. Drill out, as stated prior. I would get a shop to weld it (shouldn't be much, as you already wire wheeled the area). You'll be good for another 30 years after that.

Important thing is to stop the crack from continuing.
 

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Discussion Starter #7
I used a dremel grinding stone to clean up the crack and it's definitely split there. Drilled a hole at the end and tightened a short screw there, since my rivet gun couldn't get close enough. Hate to say it, but a little JB Weld over the crack. I also ordered the upper BMR torque box reinforcement plate kit for piece of mind.

So in getting ready to install the kit, I pulled the back seat and found the original owner must have had some stereo equipment mounted behind it. A few self tapping screws with large washers pierced the sheet metal, probably for amplifier grounds. I'm wondering if he hit that torque box from the inside. I'll have to take some measurements from the seat belt mount and verify underneath. I still find it odd for the location of that crack, as nothing else underneath looks stressed or torn.
 

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Discussion Starter #8
Well, the upper BMR torque box reinforcement plate kit is installed. What a PITA! the horizontal bolts weren't long enough, had to buy new grade-8 hardware. The vertical bolts seem anything but vertical. I had to cut the angled spacers down. Then pull it apart, paint it, let dry and reinstall. At least it's a done deal now. You can see my hack job JB-Welded bolt to stop the original tear on the left.

1064547
 

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If you don't plan on doing any drag racing or road racing at all then you should be ok. If that changes you might want to see about having the uppers welded a little better to the body and also address the lowers.
 

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Just slow the car down, problem solved.

ks
 

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Discussion Starter #11
Ha! This car isn't driven hard. It's a NA low 13 sec. street driven car. It's been to the drag strip a few times in its life, for "test and tune" events, but never launched hard. Tried drag radials once, but even then had poor traction and bad 60' times due to lack of weight transfer with the old stiff 800# front spring setup. If I had to guess, the torque box damage was due to unintentional wheel-hopping by the prior owner when it had stock control arms.
 

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You’ll eventually run into issues not having them welded. At least I did.
 

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I bought a used 1991 LX 5.0 coupe automatic as my first mustang in 1996 and after having it up in the air in the garage (heard noises) found the factory upper control arms had started to come apart from all the stoplight and stop sign launches the previous owner did, that and he had 17 speeding tickets with it and his Ford Ranger combined. :oops: Changed control arms and strengthened the chassis and all was fine.
 
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