I'm planning on cutting off the top of a '82 malibu 4 door, please tell me how and where I need to stiffen the chassis and body so this thing won't open like a flower.
Is there a web site related to this topic?
Thanks a lot.
Generally convertibles have extra bracing in the frames and also the rocker panels............The frame on your car, being a perimeter frame, runs right next to the rockers. You may end up fusing the 2 together to stiffen your car.
I have tougth of welding the body to the frame thus making it a unibody, well sort of, but I wonder what consecuenses this mod could make, has anybody made this before? will it squeal badly or crack the windshield or pop the bondo off?
thanks for answering.
A two door would be hard enough to strengthen. A four door would be really hard as they get their strength from the roof. The B pillar will have to be triangulated some way to stop it from swaying in the breeze. As well you will have to strengthen the body behind the rear doors to stop it from flopping around.
Is this a serious conversion... like you're going to fabricate a top and do it right... or is this taking a junker and making it topless?
If its the first one, consider adding bracing across the bulkhead behind the rear seat, box the frame beteen the wheels (don't worry about front and rear), and put a triangular brace under the hood that ties in the upper shock mounts on the frame to where the cowl meets the firewall. The middle is just going to be floppy, no getting around it. You can maybe have luck adding another body mount or two under the doors to tie it into the frame more rigidly.
If its the second one, take out the body mount bushings and weld the body to the frame
it is now a junker but want to make it a very nice daily driver, 350/350, maybe a turbocharger that is laying homeless around the shop, will have no top, not even a ragtop, will be for sunny days only, I like a lot the idea of welding the body to the frame, I think all the above mods will be made also, my main concern now is what will happen without the rubber bushings, how will it behave?
thanks for answering.
It will ride slightly rougher without the body bushings, but will be much stiffer. Take a look under some 50s convertibles. They all have "X" bracing in the center. I don't recall how the frame is made on your car, but if it's like the 70s Chevelle frames the rails under the body are very light with heavy rail sections in the front and rear. I'd cut the light sections out and replace with 11 gauge rectangular tubing the same size as the heavier rails. Then make an X section from where the frame starts to widen in front and back. The center will have to have room for the driveshaft. You can leave a 6" or so section out and weld a plate on the top and bottom, leaving the center open. Some of the 50s convertibles did that, with the bottom plate bolted on for easier driveshaft removal.
BEFORE you cut the top off, weld or bolt a brace from the dash along the inside of the car to the rear above the wheel well on both sides, and across the car from B pillar to B pillar. That will keep the body straight while you cut the top off. Otherwise it will warp out of shape.
If you keep the rubber body mounts you will need to add some between the frame and B pillar to keep it stiff. Weld a strengthening bar of some sort to the body between the B pillars in the floor, and extra bracing behind the rear seat for the C pillars. A piece of 20 gauge sheet metal welded to the existing behind rear seat bracing would probably be enough.
It will take a good bit of work to make this idea work right, but it can be done. Will it be worth it though? That's up to you, and what you want from it!
This is a 79 Chrysler Cordoba, no frame to speak of. We strengthened it by welding a pair of u-type signposts as half-*** subframe connectors. Works great!
Its just a $100 car that we bought specifically for this purpose. Firstly, I would get a 2 door, 4 door is gonna be tougher. Also, it pretty much has to have pillarless doors.
Mostly, don't bother pretending you are gonna make it nice. Especially if its a 4 door, cutting the roof off is easy, making it nice is not. That and the GM "framed" cars of that era had pathetic excuses for frames, basically they were unitbodies with bolt-in subframes, that happened to be connected with some really thin c channel. Its gonna flop around. Either way, I'd use this as a learning experience.
We started by just using a recip saw with a nice long blade to take out the back pillars first, and then used a tape line above the windshield as a guide for the front cut. doing it again, I would remove the windshield, ours cracked. It has a small crack to start off, but when we were done, it went across the whole thing.
Strength is OK, not railroad trestle, but no stability probs, doors open fine, etc.... This car was actually "balanced" in that when resting the roof had no stress on it, so when resting its all straight, when its on jackstands, the doors stick a bit.
Oh, as far as "pillarless dorrs", what I meant was "frameless windows".
It was a little flexed with the jackstands, those front ones were probably within a foot of the cars center of gravity, you could just lift the back end up by the rear bumper. In fact I gave myself a hernia doing just that... ain:
The car is off the stands and has been for weeks. Those pics are from quite a bit earlier. Its fine with the weenie "connectors." I will probably stack a senond layer of signposts to tie it up more. You can just feel it wiggle over bumps, the steering wheel just barely ocsillates noticibly around in reference to your butt. You can feel it if you look for it, but not otherwise, and only over bumps. It would be good as factory if only we had a non-rusty car, and just spent the $50 on proper sized rec tube to connect it right, and tied the front subframe to the rockers.
also, the car is a rusty pile. the lower quarters are pretty much gone (left one IS gone), the rear rockers are rotted out, rear floor is "soft" at best..... Its a 200,000+ mile indiana body... if anything, it will be patched with fiberglass, great stuff foam ,and bondo. Then painted with rustoleum, just for practice working filler and shooting paint more than anything else.
as with anything, if you do it one, you have tons of advise for a second run. My advise is:
1) get a solid full framed car. this pretty much leaves you with full-size fords. chryslers have been units for decades (can be ok, if solid) and gm frames are mostly thin n' weak. lincoln mark series (and platform mates) have full length boxed rails, if im not mistaken. that would be my #1 choice.
2) make sure it has all the parts you want. ours didnt come with a bumper. ever see a 79 cordoba in a junkyard? niether have we..... hence the welded stack of pipes on there now..... a $500 common car your are just lopping the roof off of is not worth spending few hundred bucks chasing parts down for.
3) remove the windshield when cutting, else you will risk cracking it. that whole a-pillar assembly willl jump a lot while sawing.
4) mark your cut lines with masking tape, and check and recheck by looking from different angles, so the car looks good when you are done. leave a extra 1/4 inch to spare, you can always go over it with a grinder to get it just right. your not gonna put it back if you take off too much.....