Learn me DIY convertible

I was helping at an auto auction and there was a coupe deville that sold as a "parade car" ie coupe sand roof. I have convinced my wife a classic (1940s thru early 60s) convertible could be a fun weekend cruiser that is family friendly but the availability and price of classic coupes and sedans is much more.

I know modern unibody cars would be structurally questionable if you removed say the roof, but how much impact on the structure and safety would there be in removing the roof on something that old? If I went down this rabbit hole should I plan to add in a tubular structure under the body panels to reinforce the body? How safe would the car be for the family vs a factory convertible of similar vintage?

Thanks for the help.

One key point. I live in Florida and can garage the car so I can either not have a roof, use the stock roof as a removeable hard top or fabricate a fiberglass/composite roof.

There is little to no difference on old body on frame cars when it comes to sedan vs vert. Some had an extra brace underneath, the 49-54 chevy comes to mind which had an x brace under the floor, but something like that is easily fabricated

I guess my big question would be... why? I love convertibles as much (and probably more) than the next guy, but why make your own when there are options out there?

In reply to mtn:

Lots more options and from what I have seen it should be a lot cheaper. I have seen a few cool older cars 1950a era I could get into for under 5k but not much in the way of driveable convertibles for that price. Also I can do a large coupe or sedan and have a big back seat for the kids the large body convertibles I have seen less especially stuff that has the cool old bodies.

Of I can find a convertible then awesome but not sure I can find what I want for what I want to pay.

Go for it.

Anything in the way of extra structure you can add to stiffen the body/frame will be a plus!

And yeah classic/old convertibles are pricey due to the fact that they are rare in the first place and have gotten more rare due to them rusting out sooner then a hard top. Having no roof when it rains, the interior gets wet. Get the interior wet, you get rust.

But here's the thing. No matter what you do, coupe or convertible, nothing from the 40's through early 60's is going to be "safe" for the family. No 3 point seat belts, no crash structure, etc... Compared to a modern car, they're death traps.

Yes, yes, I know...human kind survived driving in those old cars, but you get my point. When looking at it through the lens of todays' world, those old cars will never be safe for the family. I wouldn't put my kids in anything older than the mid-80s, and even that would be a bit iffy for me. Call me overprotective, call me what you will...just a chance I'm not willing to take when there are much better and safer options out there. And it's a darn shame too, because I LOVE those old cars. I bought a '65 Olds Delta 88 once with the intent to use it as a family cruise night car. I even had 3 point belts installed in it. But I just couldn't bring myself to put the kids in it, knowing the risks I was taking. Sold it...for a profit.

With the unibody stuff that started in the 60s (for American cars anyways) you'll definitely want to add whatever bracing the factory variant had, or more.

Klayfish wrote: But here's the thing. No matter what you do, coupe or convertible, nothing from the 40's through early 60's is going to be "safe" for the family. No 3 point seat belts, no crash structure, etc... Compared to a modern car, they're death traps. Yes, yes, I know...human kind survived driving in those old cars, but you get my point. When looking at it through the lens of todays' world, those old cars will never be safe for the family. I wouldn't put my kids in anything older than the mid-80s, and even that would be a bit iffy for me. Call me overprotective, call me what you will...just a chance I'm not willing to take when there are much better and safer options out there. And it's a darn shame too, because I LOVE those old cars. I bought a '65 Olds Delta 88 once with the intent to use it as a family cruise night car. I even had 3 point belts installed in it. But I just couldn't bring myself to put the kids in it, knowing the risks I was taking. Sold it...for a profit.

So I'm wrong in thinking big heavy American steel cars would just slice through whatever beer can a modern driver is in in the event of collision?

You're obviously someone experienced in these matters, I just assumed big American tank would destroy a modern car. Like a brodozer meeting a sunfire at speed. Maybe some scratches in the paint on the big tank, but a death sentence to whoever is in the beer can.

In reply to RevRico:

In some situations the modern car will appear to have taken far more damage, but the occupants of the old one will get hit with much higher G forces since the modern car is designed to crumple up to absorb the impact. Those "big american tanks" aren't really that much heavier than a modern midsized sedan anyways, and pretty much all of them are lighter than a new 1/2 ton crew cab pickup.

This is pretty much a worst case scenario, but it demonstrates things well enough. https://www.youtube.com/embed/joMK1WZjP7g

Note how the old car's passenger compartment just folds up on impact and the new one stays together. Those cars had heavy skins but not much underneath.

EDIT: You also won't be outmaneuver the wreck in a 50s American car with it's undersized brakes, terrible suspension geometry, and ~5 turn lock to lock steering with a 18" wheel. This stuff didn't really get better until the 1968MY and that was just really basic stuff like dual circuit brakes, padded dashboards, 3 point belts up front, and collapsible steering columns.

Those big american cars aren't as heavy as you think. My 1966 Cadillac is 4500 lbs - which doesn't sound like much in a world where a Camaro convertible is 4000. My Dodge 2500 is 7700 lbs.

And the Caddy has four drum brakes, lap belts and a non-collapsable steering wheels. Structurally, as a four-door hardtop, it's basically a convertible. All the weight is in the body panels, you can tell it's not a stiff structure.

I wouldn't cut the top off an old sedan, you've basically condemned the car to scrap once it leaves your ownership. You will also have a bunch of holes to fill up. We have a car at work that had the roof cut off after a tree fell on it. It looks like someone cut the roof off, it does not look like a convertible at anything closer than 50'. However, if I DID cut the top off and old sedan, I'd seriously consider welding the doors shut for structure.

It SUCKS to have to agree with the child safety issue but I do.

I sold my beloved F150 due to the lack of a middle shoulder belt even though it had seats for 5. I couldn't do that to the kid who sat in the middle.

RevRico wrote: So I'm wrong in thinking big heavy American steel cars would just slice through whatever beer can a modern driver is in in the event of collision? You're obviously someone experienced in these matters, I just assumed big American tank would destroy a modern car. Like a brodozer meeting a sunfire at speed. Maybe some scratches in the paint on the big tank, but a death sentence to whoever is in the beer can.

A lot of modern cars are heavier than those "old heavy cars".

The fullsizes were huge, to be sure, but some of the GM A-bodies were sub-3400lb, and those were full frame and all iron drivetrains. Modern cars, we're told that this is light and sporty.

In reply to Keith Tanner:

Agree with this.....the sedans I have seen turned topless look awkward to me. Maybe a two door coupe that was nearly identical to the convertible version might be ok....I've seen some 4 doors converted and they look odd at best. Regarding safety, I wouldn't stick my kids in a MG TD as an everyday commuter, but sure would buckle them in for the experience, and always have.

As said, most of those cars that have had the roof cut off look like a hardtop with the roof cut off... Unless you're a talented body man who can smooth out the rough edges they aren't very pretty. Plus, they obviously won't have a folding top so if it starts to rain you're out of luck.

Keep looking, a true convertible in your price range may show up eventually.

modern cars are designed to crumple and protect. Old cars were designed to decapitate...

I think old cars were a 15 mph crash test and would fail. Modern standards are 45 mph? There is a HUGE difference in teh safety between teh cars.

In reply to Mad_Ratel:

There weren't crash tests. Cars in the timeframe we're discussion were designed for looks, mainly. It took governmental regulation taking effect in 1968 for us to get glass that turns into large dust instead of jagged shards, brake systems that still work if you blow a line or a wheel cylinder, steering columns that won't Hoban Washburne you in a frontal collision, and a bunch of other things I can't think of at the moment.

The bumper rules in the 1970s were to prevent costly vehicle damage in the event of a mild collision, had nothing to do with safety at all...

BrokenYugo wrote: In reply to RevRico: In some situations the modern car will appear to have taken far more damage, but the occupants of the old one will get hit with much higher G forces since the modern car is designed to crumple up to absorb the impact. Those "big american tanks" aren't really that much heavier than a modern midsized sedan anyways, and pretty much all of them are lighter than a new 1/2 ton crew cab pickup. This is pretty much a worst case scenario, but it demonstrates things well enough. https://www.youtube.com/embed/joMK1WZjP7g Note how the old car's passenger compartment just folds up on impact and the new one stays together. Those cars had heavy skins but not much underneath. EDIT: You also won't be outmaneuver the wreck in a 50s American car with it's undersized brakes, terrible suspension geometry, and ~5 turn lock to lock steering with a 18" wheel. This stuff didn't really get better until the 1968MY and that was just really basic stuff like dual circuit brakes, padded dashboards, 3 point belts up front, and collapsible steering columns.

This video is exactly the type of thing I was going to search for when I got home.

Forgot some of the laws of physics for a minute. And I guess I was off on my mass guesses as well, I'm actually surprised to learn Keith's caddy weighs less than my Vic.

I was thinking a big heavy body on frame would just tear through a crumple zone, not thinking that while the crumple would absorb impact, that's still a ton of inertia for those in the "solid" vehicle to withstand. I guess I was thinking more "iceberg meet titanic".

Yeah, you don't really get into the whole "I win automatically because mass" deal until you're hitting an old bug with a medium duty dump truck or something to that effect. It's really interesting looking at cars that were wrecked hard and seeing where the energy went, modern stuff (mid 80s onward) mostly keeps the deformation out of the cabin and limited to the point of impact, crash a 50s car hard and every panel on it will be tweaked.

A 55-57 Chevy is only something like 3200-3800lbs depending on body style, options, and trim level, that's late model Honda Accord weight, it's just that the Accord has most of it's steel in the rockers, pillars, integral roll hoops, etc. surrounding the passenger compartment instead of a heavy gauge car shaped shell hung over a fairly flimsy ladder frame

Yep, old cars flat suck when it comes to crash protection. Sorry to be a pig, but look at it this way...there are women that carry their weight in all the right places, then there are women that carry it in all the WRONG places. Guess which car is a '50s barge is and which a '17 Accord is, even though their weights are fairly similar.

I'd rather have a wreck in a Toyota Yaris than a '60 Chrysler.

Klayfish wrote: Yep, old cars flat suck when it comes to crash protection. Sorry to be a pig, but look at it this way...there are women that carry their weight in all the right places, then there are women that carry it in all the WRONG places. Guess which car is a '50s barge is and which a '17 Accord is, even though their weights are fairly similar. I'd rather have a wreck in a Toyota Yaris than a '60 Chrysler.

the 50's car definitely has the weight in all the right places. that chrome is gorgeous.

i'll take the style and the risk that i'm taking something that old and unsafe out for a cruise once a week and strap my kids in the back. we're not commuting with them at peak traffic hours every day, we're going out for dinner after most people are home and off the road.

i don't do the "will someone please think of the children" argument.

Klayfish wrote: But here's the thing. No matter what you do, coupe or convertible, nothing from the 40's through early 60's is going to be "safe" for the family. No 3 point seat belts, no crash structure, etc... Compared to a modern car, they're death traps. Yes, yes, I know...human kind survived driving in those old cars, but you get my point. When looking at it through the lens of todays' world, those old cars will never be safe for the family. I wouldn't put my kids in anything older than the mid-80s, and even that would be a bit iffy for me. Call me overprotective, call me what you will...just a chance I'm not willing to take when there are much better and safer options out there. And it's a darn shame too, because I LOVE those old cars. I bought a '65 Olds Delta 88 once with the intent to use it as a family cruise night car. I even had 3 point belts installed in it. But I just couldn't bring myself to put the kids in it, knowing the risks I was taking. Sold it...for a profit.

As much as I like cool old cars this is why I passed on a '63 Falcon convertible and I'm shopping for a 2015 or later Mustang V6 convertible instead. Modern crash structure, air bags, ABS brakes, etc. etc. My co-workers all say "Get the 5.0!" but how fast am I really going to go with the 2 kids in the back seat?

What a bunch of spoilsports. Guess I better haul my '61 Bonneville to the junkyard before it kills me.

The only thing I know about home made convertibles I learned in a Hyundai Excel. The most important lesson was never open the doors with people in the car.

My kids love riding in my 78 zephyr. Its lap belt only and weighs a whopping 3280 right now. Guess im not as paranoid as everyone else. I say go for it.