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early c3 frame verses 73 and later?

Old 01-10-2019, 12:00 PM
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20round
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Default early c3 frame verses 73 and later?

ok, i know that 68-72 are identical frames or almost. i know, 68 had different front bumper bracket bolt spacing in the front frame horn..i know in 69 they started adding the angle supports on the kick ups. and that carried on thru the rest of the years..so what needs too be done too a 76 frame too work with a 68-72 ? is it worth the trouble? give me your thoughts guys! thanks troy
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Old 01-10-2019, 12:08 PM
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crf311
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Rear section needs to be modified . Don't remember what though. I believe it's doable.
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Old 01-10-2019, 12:12 PM
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Easy Mike
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Originally Posted by 20round View Post
...so what needs too be done too a 76 frame too work with a 68-72 ? is it worth the trouble?...
IMHO, no.
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Old 01-10-2019, 04:07 PM
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derekderek
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PM David Howard. He is best frame guy I can think of. pretty sure it's just removing the bumper shock stuff though. And since it's underneath the car, nobody really sees it all that much.

Last edited by derekderek; 01-10-2019 at 04:08 PM.
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20round (01-11-2019)
Old 01-10-2019, 05:31 PM
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bazza77
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The 69 frame horns won't even be close to fitting the front of a 76 frame. Extra holes need to be made in the horns .



69 body into a 78 frame , so far so good !
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Old 01-10-2019, 07:43 PM
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loup68
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The additional kick-up bracket before the rear wheels started in later 68 frames. I have a GM replacement frame under my 68 coupe.
It fits 68-74 cars only. Lou.
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Old 01-10-2019, 08:19 PM
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71yellow454
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73 body onto a 76 frame. Didn't modify the frame at all. I reconfigured the rear bumper brackets to fit the 76 frame. Worked out fine.

Last edited by 71yellow454; 01-10-2019 at 11:20 PM.
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20round (01-11-2019)
Old 01-11-2019, 09:44 AM
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Rescue Rogers
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Besides the holes and the bracing, The body mounts are at different heights, the rear frame crossmember is different. Those are the only welded differences. There are alot of threads on this

https://www.corvetteforum.com/forums/c3-tech-performance/4214140-1968-1972-frames-question.html

https://www.corvetteforum.com/forums/c3-general/4188982-frame-questions.html

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20round (01-11-2019)
Old 01-11-2019, 11:36 AM
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David Howard
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Originally Posted by 20round View Post
ok, i know that 68-72 are identical frames or almost. i know, 68 had different front bumper bracket bolt spacing in the front frame horn..i know in 69 they started adding the angle supports on the kick ups. and that carried on thru the rest of the years..so what needs too be done too a 76 frame too work with a 68-72 ? is it worth the trouble? give me your thoughts guys! thanks troy
You are correct on the 68-72 frames. Kick up supports added in late 68 and continued on through 82. Front horn holes moved in 73 to accommodate the new front rubber bumper.
In the rear of the frames the 68-74 are the same frame setup. In 74 they added an external dampening system to absorb impact from a rear end collision. In 1975 they replace that with a newly designed impact shock absorbing part. (Shown in picture below).


The 1976 frame is quite different as mentioned by several people, specifically the rear part of the frame that is squared off to accept the shocks mentioned. Here is a 1976 frame and you can see the space where those shocks are mounted.


Compare this rear with the rear of a 1969 and you will see that height and shape are different. This is a 72 frame for comparison, I used this frame on my 1972 road race replica build.




And here are three drawings showing the dimensional differences and similarities.




So I guess anything can be done if you want to do it badly enough. I have never made this modification myself when there are so many good frames in the correct configuration to work with it seemed pointless to me to do this much work and maybe get it right, maybe not, but that is just me.

Note the drawings are copywrighted and are being shown only for comparison purposes. Reproduction of them is protected.

Good luck with your decision and I hope this was helpful.

David
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20round (01-12-2019)
Old 01-12-2019, 06:53 PM
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thanks david for the info.. i was just at chucks today looking at a 76 frame he has. and he said you did his frame resto. i am gonna keep looking for now.. hopefully i find one in my price range..
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Old 01-12-2019, 06:58 PM
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David Howard
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Originally Posted by 20round View Post
thanks david for the info.. i was just at chucks today looking at a 76 frame he has. and he said you did his frame resto. i am gonna keep looking for now.. hopefully i find one in my price range..
I enjoyed helping Chuck with his 68. Great project for a great guy. I'll send you a PM.
David
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Old 01-12-2019, 07:08 PM
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My ears were ringing. Nice write up on the frames David!
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