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Opeler
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Discussion Starter · #1 ·
Making a Convertible

I finally got my GT and was planning (for the last 15 years) to make a ground up restored convertible. I see some archived posts from people that have made them and was wondering what the long term structural problems have been. Bob, I read one of your posts describing the reinforcements that you did and was wondering if you had any pictures of what you did. Also any horror stories or success stories would be greatly appreciated. I am just in the process of building my rotisserie for the car to make working on the underside easier so I've got plenty of time to change my mind.

Thanks

randy
 

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Re: Making a Convertible

show no go said:
Bob, I read one of your posts describing the reinforcements that you did and was wondering if you had any pictures of what you did.
I can't access my photos for now, my computer has that new virus and I can't access the internet for the moment from home. They're not very good photos anyhow, kinda grainy since the place the GT is stored is very dark. Regardless, expect to spend 60-80 hours with the reinforcements before cutting the top off your car.

As far as a convertible top, you're on your own. The German convertible kits are big bucks....I made my Dad's a 'roadster' so to speak, it will have no top at all.

Be sure about this, it's hard to go back once you've cut the top off! You'll want to reinforce the windshield frame, and make sure you leave some of the door frame up front to allow the side windows to have some support. A roll bar is a REAL good idea too...don't trust the windshield frame to protect your head 100% in a roll-over, it won't. A roll bar will also lend some side-impact protection.

Bob
 

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Opeler
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Discussion Starter · #3 ·
Thanks, I'm not worried about the time this will take to do right since my plan is to have the car on the road in about 3 to 4 years anyway. I have a fabrication shop at my disposal so I have the means to bend/cut etc. whatever I need. I have customized some vehicles with frams and rebuilt newer cars with unibody, but never customized a unibody car. I don't see much of a problem bracing for the center deflection of the car but am a little concerned about getting the lateral stability solid enough. How did you brace for the lateral flex and keep the work hidden?

I had originally planned on just making a roadster since this thing probably won't come out if it sees clouds, but my wife thinks I need a top just in case. I've measured and plan on modifying a Miata rag top to fit the project.
 

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I haven't done any calculated testing to check for lateral and torsional stiffness (yet). But, prior to my adding the reinforcements, the car doors could not be opened if the car was not on level ground. Now, with all the reinforcements, I can jack the car by one corner and both doors open smoothly while maintaining alignment. One of the keys was the 12 gauge steel inner rocker panels, and the tying-in of the rollbar to the sides of the car, the rear of the car, and to the rocker panel reinforcements. I also have frame 'connectors' tying the factory unibody framerails to the rear jacking points.

Bob
 

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I haven't converted an Opel. But I have some info.

Closed sections (tubes, pipes) are many times torsionally stiffer than open sections (sheets). Bodies are typically a several open sections. A couple 1.5" square tubes are probably about as torsionally stiff as a car body. Adding the equiv. of subframe tube connectors (Opel don't have traditional subframes) helps a lot.

Beyond torsion, you'll need to provide stiffness and strength for flexure. Most convertibles have large reinforcing plates added (kinda like a second floorboard). In a typical car the reinforcing adds 250#. Controlling flexure at the firewall is difficult due to space restrictions (causes cowl shake). Many cheap conversions are done by welding the doors shut. I doubt they'd open anyway. Some roadster kit cars use a space frame (tubes/angles) chassis. That'd eat up room in an Opel GT.

Below is a pic of the GT guts before the body panels are added. The guts weigh a bunch. Those thin roof bars add a lot of flexural stiffness. Adding material to the floor is less effective.
 

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when the back of the gt is rounded over (the panel that the gas filler tube comes out of,) what happens there is that all cut out and a flat piece of sheet metal welded in?
 

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Opeler
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Discussion Starter · #8 ·
Thanks GT Freak for the great cutaway Pic!

I don't know if my pic is going to work but here I go. I have been digging into the car looking for ideas and have found lots of little surprises. The convertible conversion is a definate project since the car needs so much metal work anyway. Floorpans are pretty bad and rocker insides need some serious help, whole rear end lid is bondo (i think the po had stock in the company with the amount he used).
If the picture loaded, the thin red is going to be some basic reinforcement made from 1" square tube between the wheel wells and complete floorpans will be plate/tube/plate construction. That will be connected to a heavily reinforced inner rocker and center console area. There will be two roll bars (yellow) that will match the height and curve of the seats and will be tied to the sides as well as a rearward brace from the midpoint of the bar to the back of the axel area. Rollbars will be secured to rockers and center reinforcements. In the front the side foot panels will be connected to the floorpan with formed 12ga wrap that will go up to the window frame and also tied directly to the rocker. The entire window frame will be reinforced and the front channel for the door windows will be integrated into the windshield frame for additional strength. I think with the sandwich construction on the floor and the reinforced center and rockers I can make enough stiffness to keep the car in one piece.

I like the shape of the roof and in some way it will be used as the new rear deck lid and welded into place which will add some more strength back there. I think I'lll have plenty of work to do this winter.
 

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Opel Key Master
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Covertible

Basically what I found is you have to do a custom rienforcement setup. The kit you get from C.A.R.S. isn't going to cut it. One thing you need to keep in mind is this: No matter how you stiffen it, the body will flex at the doors unless you have some type of triangular support locking it in like a roll bar. But the problem with that is door gap!!!!. We used 3/4 rod to tie it in that was internally threaded on both ends and then we attached some tierod ends to it. Then making maount so the rod ties in beside the seat and not affect seat fitment and up to a strengthend support above the shock tower, this allowed a strong "frame" with the ability to adjust door gaps. If you were to set your door gap and then weld in a roll bar. What typically happens is when you actually put the car on the groung or have more weight in it, the gap is going to get tighter. This is a big deal!!!! In the TN Opel Club meet pics on this site, look at my spyder convers. It had 1/4 x 2 flat bar that connects the jacking points(The the torsion bars are connected to the inner side almost middle of these bars, just beside the seats. The flat bar gave me an ideal way to connect side pipes also. Even with under support, the rear body still will push upward and the body wants to pivot behind the doors. We basically tied the ends of the flat bar , with an inner support around the shock towers. If I can get some good pic explaining this without tearing into my car, I will. Unless I have gas tank work, You won't see inside for a while
Keith
 

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GT Owner
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LENK

Opel GT Source sells a CD rom for $1 of Lenk's catalog. At the end of the section on Opel GT there is a write up (with pictures) in English and German that discusses the structural changes needed for installing their Targa kit.
 
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