Vintage Mustang Forums banner

Trunk Separator Panel

11K views 61 replies 33 participants last post by  Palo Alto Car Guy 
#1 ·
Hello everyone,
I'm considering adding a trunk separator panel to my 1970 Mustang coupe, both to increase torsional stiffness and to reduce the chance of fiery death in the event of a rear-end collision. I figure I'll just take a flat piece of metal and cut it into shape.
I've seen both aluminum held in with sheetmetal screws, and steel welded in. I imagine welded-in steel would do significantly more to increase torsional rigidity, but would be much harder to remove in the future. For anyone who's welded in a "trunk firewall," was rear shock nut access a problem afterwards? My interior is still out at the moment, so welding is not a problem.
Thanks!
 
#3 ·
Accessing the shocks would be darn near impossible unless you had a removable center panel to reach them.

I've never bothered to do this. Shark bite is more common than Mustang Flambé.
 
  • Like
Reactions: Mustmatt
#9 ·
I've never bothered to do this. Shark bite is more common than Mustang Flambé.
Very true. If the flaming Mustang gas tank explosion was a typical thing, then we wouldn't have Kelly hanging out with us after Jane took a 45 mph shot to the trunk area.
 
#5 ·
You might want to think about a Tank Armor plate instead of going through all the hassle I envision you having making a separator plate to bolt/weld to the back of the rear seat frame (I'm assuming this is your intent). Much better than your plan (IMO) and a whole lot easier. It's what I'm doing for my car.

Search - Tank Armor

I put Tank Armor in my 66 Vert project. Reasonably impressed with the strength. Seems to add a lot of rigidity and blocks the tank from the trunk largely. I have a sheetmetal piece for the divider but i am thinking about not using it. Not only would I need access to the shocks but the convertible pump as well.
 
#11 ·
There was a while where I fretted about a Pinto event, I think there is a youtube of a mustang taking a rear hit and fuel blasting into the cockpit of a coupe through the rear deck speakers or something. I considered bolting my fuel tank in from under the car, never really checked to see if it was possible. I read that the issue is the tank comes into the car instead of going under it in a big collision. Tank armor does not fix this problem. But this is another mental exercise that never accumulated true momentum...


https://www.cbsnews.com/news/mustang-a-classic-danger/


Now after rereading this its got me thinking again - if I did anything, it would be removable.
 
#26 · (Edited)
There was a while where I fretted about a Pinto event.

In 1972 I was sitting at a stop light in a 66 and was rearended by a then new Pinto Wagon. The driver had his head turned to talk to his passenger (I saw it in my rear view mirror.) His car smashed in the back of my car (dead center) and dented my fuel tank but neither one of us went up in flames . . . .
 
#13 ·
Thank you all for the replies. I know it won't be perfect fire protection. I'm also considering this for the stiffness increase, there's a guy who measured his torsional rigidity before and after mods and just screwing in a trunk separator added 14% to his total torsional rigidity.

I think I will probably hold off for now, get the car back together, and then add a screwed-in one later since it pretty much has to be removable anyway. I have enough on my plate at the moment, trying to get the car back together for a June road trip while working full-time.
 
#14 ·
I say you wouldn't have a problem with or without it. I don't have a picture of my trunk at the moment, but it looks like mine has a piece of metal behind the rear seat itself. I also have no carpet in the back trunk. I had no problems when driving it around the neighborhood on Sunday. I would say go with what you think is best, but going without it would also be ok.
 
#15 ·
This is one of those problems like "What if I was holding a jerry can full of gas, when lightning strikes me?"

Not saying that people don't get into wrecks, but honestly, you'd have to get REALLY gobsmacked before this would be a problem. If you're safety conscious, shoulder belts and decent headrests (to prevent whiplash) would rank far above a rear firewall.

However, there's more than one good reason to put one in - including the chassis stiffening, which is a very good thing.
 
#16 ·
I installed one in my 69 Coupe & covered it on the interior side with Fat Mat. The panel came with sheet metal screws, but I bolted it in.

 
#18 ·
I plan to make one for my 66 and I really like the rivnut idea. I'll have to dig out my aircraft hydraulic riveters and get some more rivnuts when I get there.

I see it this way you can sell it to some as a safety improvement that has the side effect of making the car stiffer and quieter or you can flip that around for the car guys.
 
#23 ·
I'm not sure I buy it that it adds any measurable rigidity. If there was anything to be gained someone would sell a thicker version. There would be an obvious deficiency somewhere and that would be seen as wrinkled or cracked metal around he area. Anyone seen this?
The Cougar video above is very compelling though but I don't know enough to say what might be different in them.

I have one and its worth it just to have a place to mount an amp to. When I got mine so long ago they were marketed only as "fire breaks."
 
#25 · (Edited)
There would be an obvious deficiency somewhere and that would be seen as wrinkled or cracked metal around he area. Anyone seen this?
The number of cross-braces in the rear seat that flop around from busted welds is testament enough! I've seen that with my own eyes many times.

While it may seem odd that a thin panel of steel can add torsional rigidity, this is a situation where position and leverage are everything. Much like a thin cross-brace wire can hold up a wooden slat door, and prevent it from sagging, there's no need for a huge slab of metal in there.

Another example of this is the export brace in the front. Those thin sheet metal arms couldn't possibly support the whole weight of the car - yet because of their positioning, they add a tremendous amount of structural reinforcement to the front end, and make a remarkable difference in both handling and flex reduction.

Or how about the little tabs that are recommended to be welded into the shock tower bases? Doesn't seem like a tiny piece of metal there would do much, but it keeps towers from cracking.

Sometimes just a small bit of flex that doesn't seem significant can really affect things. It's just not obvious until you remove that bit of wiggle, and feel the difference/don't have parts breaking because of it.

It's also important to note that for some of these problems to become apparent, you have to stress the car. A little 200 i6 car puttering around in town is never going to have issues with this stuff unless it rusts to the point of failure. A car with 400 horsepower, torquing so hard it has only three wheels on the ground during launch, with the nose twisted one way and tail twisted the other? Noticeable difference. It's not the gentle drivers that need additional frame bracing!

As to why it was marketed as something to stop fires and prevent flaming death? Well, in the wake of media hysteria from stupid articles like that, I'm sure they thought it was just good marketing. The fact that they didn't mention the other benefits just shows that they weren't thinking it through.
 
#24 ·
Flaming mustangs

Anyone ever see a burned mustang in any junkyard? When the moronic article came out, mustang was 35 years old. There were reports of 70 fires (all over 60 mph). That same summer, more people died from Firestone tires than all mustang fires. Re-engineering the area around a gas tank with an unproven extra piece of metal that could puncture a tank doesn't seem like good sense. Jane's FB is a perfect example of no fire and severe damage.
 
  • Like
Reactions: Grimbrand
#28 ·
I love Lee Ioccoa's comment, if you really want to be safe, its time to sell that 35 year old Mustang...


https://search.alexanderstreet.com/preview/work/bibliographic_entity|video_work|2860656


Personally, if it bothers you, do something about it, don't worry about nay-sayers, I may just put a divider in my fastback, I had it all planned but never got around to doing it. Of course I personally am not afraid of getting burned-alive-to-death, I would just do it for the "ridgidity" for performance - really - I'm not scared...:surprise:
 
#30 ·
Yea, I'm not sold on the tank armor because the fill pipe is still exposed and perhaps the tank armor would even sheer the top off but putting a plate behind the door on my fastback seems like a quick and easy way to separate me and my passengers from fuel, especially with rivnuts. Frankly, I'd take a spear to the chest but not interested in a fiery death, but hey to each his own...
 
#32 ·
The only thing that seat belts and the trunk divider panel are going to do is make it easier to identify your body.
 
#34 ·
If flaming fuel is going to come gushing out of the tank it's going to come up through the package tray area and over the tops of the outer wheelhouses.

As far as "torsional rigidity" is concerned, I don't see a heck of a lot of cars popping the rear glass and, in my opinion, better rigidity could be provided by a roll bar tied into the rear torque boxes, the inner wheelhouses and transition pan, and roof. For that matter, an "X" welded in across the seat opening with "U" channel (fencepost). Bolting or screwing a flat sheet of metal isn't going to add squat.

FWIW, if you WERE to close in the area and needed access to the shocks it would make more sense to cut rounded rectangular holes to size and use metal floor plugs.

 
#36 · (Edited)
If flaming fuel is going to come gushing out of the tank it's going to come up through the package tray area and over the tops of the outer wheelhouses.

This makes a lot of sense. Especially when you think about how the vehicle behind you (the one rear-ending) usually slams on their brakes, causing their car to dip and submarine the rear of your vehicle. This would push the tank forward & UPWARD, pushing fuel into the package tray.



Also, think about how the gas tank is installed. It's dropped in from the top, so it will naturally come out that way too.

Now, compare this to what the guys at GM did...I think GM had the better design. They had a solid floor and the tank went in from the bottom and secured with straps. The straps would be the weak point and break in a rear impact, but the tank would never reach the passenger compartment.

Here's a 66 GTO gas tank. The floor is all one piece and extends front to back...this is why they didn't make the news

 
#35 ·
I'm going to add the plate in my car, not just because of *possible* improvements in noise, rigidity, and lack of flaming death - but because I want to put a 12" sub behind the rear seat. =)

Yeah yeah, I'm a heathen. I do still want to hear the engine - I just want to be able to hear other things at times!
 
#37 ·
Well this is what happens when I read the forum late at night, but here’s a crazy idea... is there any reason you couldn’t mount the tank from underneath? Without going out and looking at the car, I’m thinking maybe you could widen the mounting holes, add some rivnuts, lift the tank up from below and bolt it in from below, add some safety straps like the GM geniuses, and then weld a plate of metal over the top in your floor... creating a level trunk floor (no more spare I guess).

Ok, let me have it, feel free to tell me all the reasons this won’t work...


Sent from my iPhone using Tapatalk
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top