Vintage Mustang Forums banner
1 - 20 of 37 Posts

·
Premium Member
1966 mustang convertible sprint 200, manual steering and brakes
Joined
·
307 Posts
Discussion Starter · #1 ·
I’ve read that filling the hole behind the rear seat with sheet metal is a good body stiffener and adds some safety against a gas tank rupture. Wondering what you guys think. Stiffening the body in this axis makes even more sense to me than even the long axis of the car.

Any suggestions on where to get a piece of sheet metal that size ? I suppose some x bracing might be nearly as effective (as a stiffener) and easier to find the metal.
 

·
Dimples
Joined
·
6,293 Posts

·
Registered
Joined
·
6,541 Posts
I remember reading an article about some testing done on the Mustang frame where the owner carefully tested the impact of different modifications on body flex. I f I remember correctly they included torque boxes, sub frame connectors and a plate behind the rear seat. The plate turned out to be one of the best at reducing flex. There is always a lot of debate whether it needs to be welded or just screwed in. Also if you don’t add ribs or other methods to dampen noise, it will act like a drum and amplify noise. Ribs would also improve the strength and resistance to flex. I haven’t seen anyone sell a ribbed plate though.
 

·
Registered
Joined
·
2,933 Posts
Its worthless to do anything against gas, I don't know where that idea comes from...your seat does about as good a job as preventing gas going anywwhere. In the event of an accident bad enough to rupture the gas tank(of which I have seen no evidence yet of it being a common problem in a vintage mustang though perhaps its happened once or twice) the gas is simply going to go over the divider anyway, there are large holes under the package tray...there are smaller cracks around the seat, etc etc etc.

As for chassis stiffening, I have heard that myself...I even ordered a divider....and then it got here and I realized what a flimsy piece of garbage it really was....so I simply installed trunk braces from an RX-8 instead:







A bit of trimming and they fit right in...I suspect they do at least as much as the flimsy sheet metal anyway.
 

·
Premium Member
1966 mustang convertible sprint 200, manual steering and brakes
Joined
·
307 Posts
Discussion Starter · #7 ·
Thanks guys. Never dawned on me to check NPD. I hear ya on the ”drum effect”. I’ve see. That played out at work with the firewall (and it’s way stiffer than a huge flat sheet would be. Think I’ll look for some cross bracing like wicked has. Thanks again.
 

·
Premium Member
Joined
·
7,710 Posts
Several years ago, I bought a freshly restored, but totaled 1966 coupe. The new owner bought it and quickly lost control, slid backwards into a telephone pole. The pole wound up almost to the rear glass, damaging the panel between the trunk lid and glass. The fuel tank was totally destroyed and the frame rails were buckled in.

I rigged a 1 gallon gas can in the engine compartment, and drove it home, on the freeway. It was bouncy, but fine.

No fire, no explosion.
 

·
Premium Member
1966 mustang convertible sprint 200, manual steering and brakes
Joined
·
307 Posts
Discussion Starter · #9 ·
Sounding more and more like urban legend. Like the spear-o-matic
 
  • Like
Reactions: C6ZZGT

·
Registered
Joined
·
2,933 Posts
Sounding more and more like urban legend. Like the spear-o-matic
The spear-o-matic is real...in cars where the steering box is mounted in front of the shock tower/control arm area....not so much in vintage mustangs. Possible in theory though...if you are hit head on by a semi truck at 90mph or something equally extreme...in other words, if the accident is bad enough for it to be a factor....it probably wouldn't be a factor anyway.
 

·
Premium Member
Joined
·
7,769 Posts
I like the cross brace idea, can even be hidden between the seat and a stock rear seat divider.
Would probably help solve the body flex that causes cracks at the base of the C pillar at the quarter.
I was in a crash in 1995, in my 66, struck in the driver side rear corner. Had to replace :
Full quarter, full wheelhouse, trunk drop off and floor, fuel tank, trunk brace, tail light panel, rear valance, trunk lid, tail light bucket, quarter extension, and yes...the fuel tank. It was creased on the corner by my driver side tail pipe. It created a TINY leak.
The laws of physics for a steel container holding a fluid that is generally at rest or traveling at the same speed as the rest of the car, then struck from behind, tell me that the amount of force required to rupture that welded steel container to the point where all that gas would first move rearward, then forward and be able to escape all at once and somehow make it UP and not down, past the rear seat divider, insulation, package tray AND the rear seat AND SOMEHOW ignite...is such an incredible amount of impact force that a gasoline leak would be the LEAST of one's worries.
If it bothered me, I would have replaced it with something other than stock, or drive another car.
It still sucked because the car had never been in a collision, was all original metal, bumpers, trim, even had FoMoCo marked bulbs in the tail and reverse lights. Oh, well.
 

·
Registered
Joined
·
77 Posts
that one from npd says it's 21 gauge. I would much rather get a sheet of something stronger and cut it myself.

Now maybe buy it, use it as a template, then sell it after.
 

·
Premium Member
1966 Mustang Hardtop 289 4 Speed
Joined
·
7,323 Posts
Its worthless to do anything against gas, I don't know where that idea comes from...your seat does about as good a job as preventing gas going anywwhere. In the event of an accident bad enough to rupture the gas tank(of which I have seen no evidence yet of it being a common problem in a vintage mustang though perhaps its happened once or twice) the gas is simply going to go over the divider anyway, there are large holes under the package tray...there are smaller cracks around the seat, etc etc etc.

As for chassis stiffening, I have heard that myself...I even ordered a divider....and then it got here and I realized what a flimsy piece of garbage it really was....so I simply installed trunk braces from an RX-8 instead:







A bit of trimming and they fit right in...I suspect they do at least as much as the flimsy sheet metal anyway.
Now that's Big Brain thinkin. 👍
 

·
Registered
Joined
·
1,644 Posts
that one from npd says it's 21 gauge. I would much rather get a sheet of something stronger and cut it myself.

Now maybe buy it, use it as a template, then sell it after.
Try some 16 ga. It won't flex and I don't think the sound would be an issue. If it were, you could apply some type of insulation material on the trunk side. Make a cardboard template to mark the 16 ga with then a plasma cutter to cut it out with, because you can't do squat to it with hand snips.
 

·
Premium Member
Joined
·
7,710 Posts
Sounding more and more like urban legend. Like the spear-o-matic
I worked in a couple salvage yards in the early to late 70's and have been in a ton more.

There was not the concern on body fluid issues back then. More than 1 car had a reversed umbrella type steering wheel, where the chest had smashed hard enough on it to invert the plastic and steel, pushing it down toward the dash. The hub area was often grossly stained with blood and other organic materials.

Sometimes the steering column was just cut off, as the body was impaled on it.

I was going through a car that had just been brought in, compact size, that belonged to a college student, where a truck had rolled over on her. I found a little white canvas deck shoe, and realized the foot was still inside, and turned it in.

While not spear o matic, the passenger side had a lot of crushed glove boxes, 1 or 2 deep dents in the steel dash from knees, and lots of hair and blood in the windshields.

In general, cloth seats were huge sponges for blood and fluids.
 

·
Premium Member
Joined
·
316 Posts
I've considered cross bracing or a plate in the rear of my Coupe for added stiffness also, may get more serious after it's running at least. I have the plate steel already, I'll have to check the gauge to make sure it's at least 16 gauge now, I can't remember where I read the suggestion of thickness when I bought it at Metal Supermarket.

As for the tank rupturing anything can happen and I'd agree that if that's your concern also I'd seal up the package tray as mentioned but then tearing metal in a rear ender may still open holes so if that's your focus then Tank Armour or similar DIY to strengthen above the tank to force the rupturing fuel down instead of into the car may be a better solution.

I had a State Trooper colleague that was rear ended in his late 90's Crown Vic, similar tank design in trunk and hanging below like Mustang. The tank ruptured, fuel entered the cabin and ignited (crushing metal causes a lot of sparks), he survived the impact but was badly burned (>75%?) and succumbed to his burn injuries after almost a month of ICU. Without the fuel entering the cabin he would have survived the physical injuries.
 
  • Like
Reactions: Husky44

·
Registered
1965 Coupe C-Code
Joined
·
873 Posts
I worked in a couple salvage yards in the early to late 70's and have been in a ton more.

There was not the concern on body fluid issues back then. More than 1 car had a reversed umbrella type steering wheel, where the chest had smashed hard enough on it to invert the plastic and steel, pushing it down toward the dash. The hub area was often grossly stained with blood and other organic materials.

Sometimes the steering column was just cut off, as the body was impaled on it.

I was going through a car that had just been brought in, compact size, that belonged to a college student, where a truck had rolled over on her. I found a little white canvas deck shoe, and realized the foot was still inside, and turned it in.

While not spear o matic, the passenger side had a lot of crushed glove boxes, 1 or 2 deep dents in the steel dash from knees, and lots of hair and blood in the windshields.

In general, cloth seats were huge sponges for blood and fluids.
The reason people say they never hear about the horrific accidents is because no one talks about them. They didn't put them in the newspaper back in the day. But ask the people who have to clean up the messes and it's a different story.
 

·
Registered
67 Fastback T5 331 TCI Frt End, Canted 4 link rear susp
Joined
·
1,146 Posts
I like to add rigidity as much as the next guy, but I once read something that said "any time you stiffen one area, you are transferring that load or force somewhere else". In the case of this back seat area, I'm wondering how much benefit is actually gained? Is there really much side load on the back seat area? And if there is, where is the load being transferred to? Looking at this photo, it seems if we stiffen our front and rear ends of the vehicle, wouldn't the stress end up somewhere like in the yellow circle, or maybe the area of the A-pillars? Just food for thought...

Vehicle Window Motor vehicle Hood Automotive tire
 

·
Registered
Joined
·
2,933 Posts
I like to add rigidity as much as the next guy, but I once read something that said "any time you stiffen one area, you are transferring that load or force somewhere else". In the case of this back seat area, I'm wondering how much benefit is actually gained? Is there really much side load on the back seat area? And if there is, where is the load being transferred to? Looking at this photo, it seems if we stiffen our front and rear ends of the vehicle, wouldn't the stress end up somewhere like in the yellow circle, or maybe the area of the A-pillars? Just food for thought...

View attachment 810970
Possibly...but its also transferring less overall load than it was before the stiffening. On this subject, here's an old Stangnet thread that is always worth a read for those interested in this type of thing...One thing to note...the rear seat divider did have a huge impact in this test(relative to other modifications at least):

 
1 - 20 of 37 Posts
Top