Re: Thank you
His second post on the subject may address the issue. (still can't get the link to work.)
Re: How do you tell factory A/C on 69 427?
Rolf Krueger -- Sunday, 5 December 1999, at 12:33 p.m.
1. On ALL 1968-1970 Convertibles, the vents that are on top of the rear deck panel are FORWARD of the vertical cargo compartment bulkhead, assuming that the vehicle in question is in the same configuration as it was when it left the St. Louis assembly plant. In order to keep water from entering the cargo area, a hard fiberglass plenum is directly underneath those vents to carry water away. In these convertibles, the water drains through some passages that are internal to the rear bulkhead area and hard to trace unless you have the body apart and off the chassis. Note that on 1968-1970 Corvettes, the forward portion of the fuel tank almost touches theat vertical rear bulkhead; you can just barely get a finger between the tank and the bulkhead.
2. Chevrolet made a significant design change beginning in the 1971 Model Year; the vertical cargo compartment bulkhead was moved forward 3 inches. This increased the "rattle space" between the front of the fuel tank and the rear bulkhead significantly; after this change, you can get your entire arm between the fuel tank and the rear bulkhead. This change made the inside of the rear compartment smaller and had secondary effects on the design of the rear area carpet and the location of the convertible deck lid hinges.
3. The change in the location of the vertical rear bulkhead for 1971 and on had a lesser effect on coupes, because the rear deck vents on coupes are not as far aft as they are on convertibles. The design of the under the deck plenum (on coupes) that collects water and routes it out into the fender wells through those rubber hoses was not impacted by this rear bulkhead location design change. The design of the rear bulkhead itself was significantly affected, however.
4. The design of 1971-1973 convertibles was much more significantly impacted by moving the vertical rear bulkhead forward. That is because those rear deck vents was no longer forward of that bulkhead and you no longer had to worry about water getting into the cargo area from those vents. This eliminated the need for that under the deck fiberglass plenum. Note that Chevrolet did not change the design of the actual convertible rear deck panel (or the relative location of those vents) because they wanted to minimize re-tooling costs. They just changed what was below that rear deck.
5. With the help of some other NCRS members, I have researched this matter extensively by inspecting a lot of cars (especially wrecked or disassembled cars) and by following the engineering paper trail. It all very consistently fits together. Several years ago, I wrote an article on this for the Texas Chapter Newsletter. I have found that many people (even very experienced judges) don't realize that this rear compartment change was made. I hope this helps you better understand this matter.
I too would like to have the extra room. Glad not to have the rattle that the General must have been addressing though!
Mike
His second post on the subject may address the issue. (still can't get the link to work.)
Re: How do you tell factory A/C on 69 427?
Rolf Krueger -- Sunday, 5 December 1999, at 12:33 p.m.
1. On ALL 1968-1970 Convertibles, the vents that are on top of the rear deck panel are FORWARD of the vertical cargo compartment bulkhead, assuming that the vehicle in question is in the same configuration as it was when it left the St. Louis assembly plant. In order to keep water from entering the cargo area, a hard fiberglass plenum is directly underneath those vents to carry water away. In these convertibles, the water drains through some passages that are internal to the rear bulkhead area and hard to trace unless you have the body apart and off the chassis. Note that on 1968-1970 Corvettes, the forward portion of the fuel tank almost touches theat vertical rear bulkhead; you can just barely get a finger between the tank and the bulkhead.
2. Chevrolet made a significant design change beginning in the 1971 Model Year; the vertical cargo compartment bulkhead was moved forward 3 inches. This increased the "rattle space" between the front of the fuel tank and the rear bulkhead significantly; after this change, you can get your entire arm between the fuel tank and the rear bulkhead. This change made the inside of the rear compartment smaller and had secondary effects on the design of the rear area carpet and the location of the convertible deck lid hinges.
3. The change in the location of the vertical rear bulkhead for 1971 and on had a lesser effect on coupes, because the rear deck vents on coupes are not as far aft as they are on convertibles. The design of the under the deck plenum (on coupes) that collects water and routes it out into the fender wells through those rubber hoses was not impacted by this rear bulkhead location design change. The design of the rear bulkhead itself was significantly affected, however.
4. The design of 1971-1973 convertibles was much more significantly impacted by moving the vertical rear bulkhead forward. That is because those rear deck vents was no longer forward of that bulkhead and you no longer had to worry about water getting into the cargo area from those vents. This eliminated the need for that under the deck fiberglass plenum. Note that Chevrolet did not change the design of the actual convertible rear deck panel (or the relative location of those vents) because they wanted to minimize re-tooling costs. They just changed what was below that rear deck.
5. With the help of some other NCRS members, I have researched this matter extensively by inspecting a lot of cars (especially wrecked or disassembled cars) and by following the engineering paper trail. It all very consistently fits together. Several years ago, I wrote an article on this for the Texas Chapter Newsletter. I have found that many people (even very experienced judges) don't realize that this rear compartment change was made. I hope this helps you better understand this matter.
I too would like to have the extra room. Glad not to have the rattle that the General must have been addressing though!
Mike
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