68-75 Convertible Top Frame Differences?

[Chuck G.]

Are there any minor differences among 68 to 75 convertible tops? My 69 was a hardtop only car, verified by the tank sticker. A previous owner in 1975 added a soft top. My windows fit like boots on a rooster. No matter how hard I try, I can't get the windows to go up "all the way". I have about a 3/4 inch gap at the top of each. I've put about 20 hours into adjustments. The soft top is very hard to put up and down. The front header hits the decklid when I put the top down. I have to "overopen" the decklid to get the header to clear. It's a real pain to put it back up too...a 2 man job...very tough to align the pins. I want to put a new convertible top on the car. Should I be looking for a "correct" 69 frame too? I though they were all the same with the exception of the size of the pins on the rear...68 being thinner. Any suggestions? Chuck

[Joe L.]

Re: 68-75 Convertible Top Frame Differences?

Chuck-----

I don't think that there are any significant differences between any of the 68-75 soft top frame assemblies. Certainly, there are none that should affect interchangability. Although there originally were two different soft top frame assemblies, 68-69 was GM #3914594 and 70-75 was GM #3977794, I am certain that the later assembly is fully retrofittable to 68-69 since, when GM discontinued the 3914594 in about 1979, they specified the 3977794 as the SERVICE replacement for ALL 68-75 Corvettes.

The problems which you describe with your soft top are, save for one, EXACTLY the same as those that I experienced with my 69 when I added a soft top in about 1986. From inquiry with/observation of other 68-75 convertible owners, most of which cars were original soft-top only, they had about the same problems, too. So, I don't think that the problems which you described are unique to hard top-only cars which have had soft tops retrofitted.

The one problem which you describe that I don't have is the stiffness in opening and closing the soft top. For me, it's pretty much been a one-person operation since I installed it. I would suspect that, perhaps, there may exist some corrosion at the pivot points which is causing this problem for you. As far as the other problems go, I suspect that if you were able to obtain an NOS complete soft top assembly for a 69, you would still have exactly the same problems which you are experiencing.

[Juliet P.]

Re: 68-75 Convertible Top Frame Differences?

Chuck,

My '70 has limited clearance to the decklid when going up/down. I don't have to over open the decklid, but I do have to be careful to have my hand flush and not somewhat fisted in that gap or i'll pinch it. I can get the top up/down myself but it does take some muscle, back muscle mostly!. Once I get it started it's not too bad.. just the first few inches is tough. It's lots harder than manually putting the top up/down on my '95 Mustang GT (much larger, more sound deadening in the top, glass rear window. On the pony car my hydraulic cylinder blew out about 2 years ago, of course 1 week after I spent $400 getting one side fixed the other blew out, so I put the top up manually now!. Far more reliable that way.

I haven't finished addressing my driver side glass gap at the rear yet, but when I was last playing with it I noticed that the weatherstripping was driving the window adjustment. I ended up tweaking the adjustment of the weatherstripping to get a better fit. I believe the entire top moves up & down & fore / aft at the base pivot location, where it attaches behind the seat. After consideratble hours adjusting glass I got the pass side to fit great, but the driver side isn't perfect yet.

I'm beginning to think that the skill of the installer has a lot to do with the ultimate fit. There are several places where the top is attached / cut, and if it's too short or long or even crooked side to side that can throw the whole thing off. Everything I've read & heard about (which you've probably seen too) says to get the windows adjusted to the hardtop, then don't move them, and adjust the ragtop to the windows. Since you have both you might try that approach. If it'll help to look at mine for comparison sometime just give a holler. ~Juliet


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[Chuck G.]

Re: 68-75 Convertible Top Frame Differences?

I think that the soft top installer violated the first principal of installation...fit the windows to the soft top frame...then install the top itself. I've fooled with this for many hours over many "sessions". Without exaggeration, I'll bet I've spent 20+ working hours fooling with the adjustments. I'm going to order a new Al Knoch top. Two of my buddies have become "experts" at top installation, and have offered to give me a hand doing it myself. That way, in my own garage, I can fool with the bows till I'm satisfied. The drivers window is so bad that I shimmed the upper weatherstrips "down" about 1/2 inch, and I still have a 1/2 inch gap with the window rolled up. Chuck