'68-'69 convertible under dash braces vs. '70-'75 convertible. diff's? retrofit?

[Richard K.]

Do the '70-75 convertibles have additional under dash bracing vs. what the '68 or 69 convertibles have?
If so, can the additional bracing be retrofitted to the '68 or 69 convertible?
I'm assuming that GM added the bracing to help eliminate the cowl-shake in the convertible. If so, I think they may have only eliminated some shake. I'd like to add some bracing, if easily done, and shown in a '70 through '75 AIM.
Thanks

[Keith M.]

Re: '68-'69 convertible under dash braces vs. '70-'75 convertible. diff's? retrofit?

Hey Rich, this does not answer your specific question but I believe bracing varies between an AC vs non AC car...so you may need to pay attention to that as well.

[Jimmy P.]

Re: '68-'69 convertible under dash braces vs. '70-'75 convertible. diff's? retrofit?

Hi Rich,
If you look in your 68-69 TIM&JG in the Interior Section 10. I only have the 5th edition to reference currently. It does a nice job explaining and showing AIM page views on the under-dash braces. Looking thru my 70-75 AIMs and checking out some photos I have on file from our 75-77 TIM&JG Revision it doesn't look like any more braces were added after the additional braces were added in March 1968 to convertibles with C60.
Here are a couple photos from 75 convertibles with C60 that show the added right-side braces & the brace cover extension added to hide the brace rod. (Note: the AIM pages will show all the left side bracing.) I'll email you photos of the AIM pages mentioned here for your reference. I'm sure others may chime in with more info. as far as adding more bracing/retrofitting. Keith is correct, the bracing is different in non-C60 convertibles.
Hope this helps!

[Richard K.]

Re: '68-'69 convertible under dash braces vs. '70-'75 convertible. diff's? retrofit?

Thanks gentlemen from NCRSPITT ! Nice info.
I might be asking for trouble by trying to improve on what GM did, but I wonder if any others have added any bracing, or other support, to the cowl of the convertible.

[Gary B.]

Re: '68-'69 convertible under dash braces vs. '70-'75 convertible. diff's? retrofit?

Looking through the 68, 69, 70,71 and 72 AIM's... Coupes have different bracing than convertibles. AC is different than non-AC, different design of braces and brackets. Most braces are in the same location, just different bends to clear the AC. Look at a 72 convertible with AC, it has the most bracing available. To add all those braces, it would require riveting the brackets to the fiberglass and welding other bracket and braces to the birdcage. To do that, would require almost complete removal of the interior and dash. I just wonder how much different it would really feel for all the work involved?
Gary B

[Richard K.]

Re: '68-'69 convertible under dash braces vs. '70-'75 convertible. diff's? retrofit?

Gary,
Thanks for looking at this.
I think you're right in wondering about doing all the work required, and not knowing if the end result will cure the cowl shake to any great degree.
It would probably require a structural engineer to provide the answer.
Thx

[Gary B.]

Re: '68-'69 convertible under dash braces vs. '70-'75 convertible. diff's? retrofit?

Richard,
To put this in proper context...
One of my other cars is a 1954 Nash Metropolitan Convertible. If you think a 54 Corvette is primitive, drive one of these.
When I take my 68 Corvette or my 1070 Corvette for a drive, well... if it has dash shake I sure don't recognize or feel it. Feels more like a Rolls Royce to me.
Gary B