72 LT1 hardtop renovation question

[Fred H.]

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In the process of our 72 LT1 convertible restoration, we're refurbishing the removable hardtop (new vinyl, new headliner & new weather strips). There is a chrome bezel in the center of the soft-top deck lid. Is there suppose to be an alignment pin that was stock on the hardtop? There are two small holes in the center (bottom) of the rear window channel, approximately corresponding to the bezel location.

[Don L.]

Re: 72 LT1 hardtop renovation question

Hello Fred. While I'm not totally clear on your question, I do know your '72 hardtop should have a chrome bracket attached to the bottom of the top, centered across the window width. A small carriage bolt drops down thru this bracket and into/thru the chrome bezel in the rear deck. A small (7/16"?) nut attaches against the bottom of the deck, pulling the weather strip down tight. As well, special chrome hex bolts go horizontally thru side brackets into the inside corners of the deck lid. I'm not near my car or my hard top right now, but can post photos of any part you need of our helps

[Fred H.]

Re: 72 LT1 hardtop renovation question

Hi Don, thanks for your input. Specifically my question is regarding the chrome bracket you describe (centered across the window width). I assume it is missing on our hardtop, and suspect it attaches to the top (via the 2 holes at that location in the rear window channel). If possible a photo would help. We do have the attachment studs at each side. Fred

[Mike E.]

Re: 72 LT1 hardtop renovation question

Any tips for us who are facing replacing the vinyl? How to avoid wrinkles behind the side windows, specifically. Thanks in advance.

[Richard K.]

Re: 72 LT1 hardtop renovation question

I have the same hardtop that you have. I"m away from home traveling, so I'll have to work from memory, which could be sketchy.
Check your production manual. I believe the bracket in the center rear rail/bow of the top is attached by rivets, not screws. or nuts and bolts. Also, I believe that the bracket can only be attached before the rear window is re-installed, since the rivets are angled toward the window. Also, there should be a ferrule installed in the body below the bracket hole in the convertible lid. This would require aligning and drilling to create one. If there is no evidence of there being a hole in the convertible lid, check that the rear window in the top is dated correctly for your car before you put it in. FWIW, finding the bracket probably will be difficult, and you may have to call many vendors to find one. I don't believe there is a GM part number for the bracket, but, again, check the production manual.
I'm assuming the vinyl top in your picture is a new one that has been installed. Evidence being, the clips all around the perimeter to hold the vinyl in place, and the heat gun laying on the floor.
I'm thinking that you can be of great help to all of us who are considering replacing their vinyl. Could be a great Restorer article! Do you have pictures of the process as you went?
Just a caution, I was told by two different hardtop restorers that the rear window is very fragile. It looks like you went very slowly and mythodically in your removal. Good job! Keep doing photos, and sharing. Great stuff.

Rich Kossum

[Joe L.]

Re: 72 LT1 hardtop renovation question

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In the process of our 72 LT1 convertible restoration, we're refurbishing the removable hardtop (new vinyl, new headliner & new weather strips). There is a chrome bezel in the center of the soft-top deck lid. Is there suppose to be an alignment pin that was stock on the hardtop? There are two small holes in the center (bottom) of the rear window channel, approximately corresponding to the bezel location.

Fred------


The center bracket, GM #3962670, was added in VERY late 1969. As an example of how late, my original owner, mid-September, 1969 built convertible was not so-equipped. I'm not actually 100% sure that any 1969's originally had it. All later C3's with hardtops had the bracket.

The bracket was attached to the top with rivets. As I recall, the bracket was stainless steel. The 3962670 was discontinued without supersession in April, 1981. I do not know if it's reproduced.

[Fred H.]

Re: 72 LT1 hardtop renovation question

Thank you for your input / knowledge.

I thought I would share a little history; my LT1 Convertible (factory air) has a build date of July 19.1972 ( VIN last 5 26756). Some believe it may be the last 72 LT1 convertible air car built ?

While I'm not certain, I believe the hardtop is original to this car. I understand that the 3962670 is discontinued, and will difficult to source. I've known David Sokolowski for quite sometime. And plan to start the search with David.

I believe you have advised me on my earlier queries to the Technical Discussion forum previously, I appreciate your advise.

Fred

[Fred H.]

Re: 72 LT1 hardtop renovation question

Rich, I appreciate your input. I believe you are correct that the GM 3962670 bracket was attached via rivets. Hopefully I"ll be able to source the bracket, somehow / somewhere. We will not re-install the rear glass until we install the bracket (FYI the rear glass is dated appropriate for the cars build date)

Fred

I will post the blow by blow "Vinyl top replacement" process as suggested.

[Fred H.]

Re: 72 LT1 hardtop renovation question

I plan on posting the blow by blow "Vinyl top replacement" process as suggested. FYI it is a somewhat tedious project that requires patience.

[Joe L.]

Re: 72 LT1 hardtop renovation question

All-----

To be honest, this center bracket was a "band-aid" and a VERY inelegant, "crude", and "tacked-on" solution to a problem that probably would have been better left unsolved.

I think I know what the perceived problem was: On my 1969 convertible with hardtop the hardtop bows up slightly in the middle. It's enough that the rear weatherstrip does not contact the deck-lid in the center. One can VERY SLIGHTLY "see daylight" between the weatherstrip and the deck lid. It's been this way since the day I took original delivery of the car (9/30/69). I noticed it almost right away and was initially concerned that water might get in at this point. It never did, though, and the "problem" turned out to be a non-problem.

I expect that some 68-69 owners complained about it and that's what drove the late 1969 addition of the bracket. The proper solution would have been to somehow modify or redesign the hardtop rear surface so the slight bow was eliminated or, at least, modify the rear weatherstrip so that a complete seal was achieved even with the top problem. But, I expect the cheaper solution was to design and release the bracket. It may even have been that the bracket was added to 1968-69 Corvette convertibles with hardtop if the owner complained.

To be honest, I'm very glad that my car never had the bracket. As I stated, it looks very "tacked-on", almost like an aftermarket or "bubba fix". And, then there's the unsightly hole in the center of the rear decklid when the hardtop is off the car. I had plenty of opportunity to purchase this bracket from GM when they were still available, even if I just added it to the collection and never installed it on the car. I never did, though. I feel about the same way about it as I feel about side exhaust, 3X2, and TJ-2 louver trim.

[Terry M.]

Re: 72 LT1 hardtop renovation question

All-----

To be honest, this center bracket was a "band-aid" and a VERY inelegant, "crude", and "tacked-on" solution to a problem that probably would have been better left unsolved.

I think I know what the perceived problem was: On my 1969 convertible with hardtop the hardtop bows up slightly in the middle. It's enough that the rear weatherstrip does not contact the deck-lid in the center. One can VERY SLIGHTLY "see daylight" between the weatherstrip and the deck lid. It's been this way since the day I took original delivery of the car (9/30/69). I noticed it almost right away and was initially concerned that water might get in at this point. It never did, though, and the "problem" turned out to be a non-problem.

I expect that some 68-69 owners complained about it and that's what drove the late 1969 addition of the bracket. The proper solution would have been to somehow modify or redesign the hardtop rear surface so the slight bow was eliminated or, at least, modify the rear weatherstrip so that a complete seal was achieved even with the top problem. But, I expect the cheaper solution was to design and release the bracket. It may even have been that the bracket was added to 1968-69 Corvette convertibles with hardtop if the owner complained.

To be honest, I'm very glad that my car never had the bracket. As I stated, it looks very "tacked-on", almost like an aftermarket or "bubba fix". And, then there's the unsightly hole in the center of the rear decklid when the hardtop is off the car. I had plenty of opportunity to purchase this bracket from GM when they were still available, even if I just added it to the collection and never installed it on the car. I never did, though. I feel about the same way about it as I feel about side exhaust, 3X2, and TJ-2 louver trim.

Joe
The "problem" may have been more than water entering the cockpit. When my coupe rear window is out of its position (admittedly the rear window is substantially more area than the small opening you refer to) under some circumstances fuel fumes enter the cockpit and sometimes one can smell exhaust fumes. None of these events take place at speed, but they could be concerning to some owners and some Chevrolet engineers. As we know there was an effective solution to these issues with the removable rear window and the hard and soft top in years following the build of our Corvettes.

[Joe L.]

Re: 72 LT1 hardtop renovation question

Joe
The "problem" may have been more than water entering the cockpit. When my coupe rear window is out of its position (admittedly the rear window is substantially more area than the small opening you refer to) under some circumstances fuel fumes enter the cockpit and sometimes one can smell exhaust fumes. None of these events take place at speed, but they could be concerning to some owners and some Chevrolet engineers. As we know there was an effective solution to these issues with the removable rear window and the hard and soft top in years following the build of our Corvettes.

Terry------


Yes, gasoline fumes in the passenger compartment was a notorious problem with earlier C3 Corvettes. I had the problem for years on my car. But, I had the problem even after I added a soft top assembly to the car and the rear weatherstrip sealed well. I believe the fuel odors wafted in through open windows. In any event, assuming that there was concern that fuel vapors could enter the passenger compartment through the space between the hardtop rear weatherstrip and the deck lid, that would be even more reason to correct the "gap" problem with a more "elegant", better engineered solution than the center bracket.

I believe that GM made another attempt to solve the fuel vapor problem. In late 1969 an integral pressure vacuum valve was added to the fuel tank. This valve is outside the fuel filler boot which is supposed to seal to the underside of the rear deck, so, presumably, any fuel vapors vented could not emanate from the filler door area. Unfortunately, the fuel cap was not changed to a sealed type cap for 1969. So, fuel vapor venting could continue. For 1970 and later, of course, the integral pressure vacuum valve remained AND the fuel cap became a sealed type.

In late 1970, GM discontinued from SERVICE all of the non integral pressure vacuum valve fuel tanks for 1963-69 Corvettes (except C2 36 gallon) and replaced them with tanks with the integral valve. GM also instructed that when these tanks were used to SERVICE any 1963-69 Corvette, a sealed type fuel cap was to be used. I HIGHLY recommend that anyone replacing a fuel tank on any 1963-69 Corvette use the tank with the integral pressure vacuum valve and a sealed type fuel cap. Install the original vented cap for judging only. Yes, the tanks with the integral pressure vacuum valve do have a modest difference in configuration compared to the non-valved tanks but that's a small price to pay. Also, make sure that the fuel filler boot seals well against the underside of the rear deck (actually, GM refers to the boot as a SEAL, which is exactly what it's supposed to be). Incidentally, my 1969 had the tank with the integral pressure vacuum valve but the valve eventually leaked. I replaced the tank with another identical GM SERVICE tank and used a sealed type cap. Most of the fuel vapor problem was cured.

As far as exhaust odors getting into the passenger compartment, I think that's always going to be a problem for 1968-73 Corvettes when the side windows are down. I think the "kammback" design of the rear deck has a lot to do with this. However, I can say this for absolute certain: the problem is FAR worse if the car has an inoperable or removed AIR system. That's one of the reasons I would NEVER, EVER remove an AIR system from a car I owned.

[Don L.]

Re: 72 LT1 hardtop renovation question

Hi Fred. Sorry for the delay in response and sorry too for any anxiety or difficulty this delay might have caused you.

Here are some photos of the bracket on my '72 hard top. As you can see, this one is indeed riveted in 2 places to secure it to the top. My bracket is chrome plated and is VERY magnetic. If more photos are needed I'd be pleased to shoot whatever you need.



Hope this helps...Bracket 1.jpgBracket 2.jpgBracket 3.jpgBracket 4.jpg

[Richard K.]

Re: 72 LT1 hardtop renovation question

Don's pictures are great.
I'm not sure if Mike or Don care about judging, nor do I know if it's mentioned in the current judging guide (I'm traveling and don't have access). The mounting bolt has a hole in it's bottom. I believe a rubber bumper is meant to fit there; presumably, to protect the body's paint if you should err in mounting the top. Also, on the car-body side of the mounting bracket is a triangular, very thin, piece of plastic sheeting glued there to protect the body. These items may show in the production manual. The plastic might be faintly visible on Don's photo.
My top is dated 1971, but I bought it and mounted it on my Dec 1969 car back in 1975 because I thought the vinyl hardtops really added to the handsomeness of the car. Paid $300 in '75...lol. Drilling 3 mounting holes in the convertible deck to add this top was VERY nerve-wracking. Fortunately all turned out well.

[Don L.]

Re: 72 LT1 hardtop renovation question

You're right, Richard. I should have mentioned that. My rubber tip is lost. I wish I still had it and I wish I could get a photo of it for possible replacement. That said, that bolt is far from my most fearful issue when installing the top. I wrap the stainless corner tips in heavy rubber tape to keep them from biting into the deck lid until all secure points are torqued tight and the top can't rock fore/aft. I wrap them again when removing the top.

Don