Using '73 frame for '75 coupe?
Thread Starter
Instructor
Joined: Oct 2008
Posts: 105
Likes: 3
From: Richmond Tx
Using '73 frame for '75 coupe?
Restoring '75 coupe, and have a chance to by restored '73 vert rolling chassis. Question...can i use the 5mph bumper hardware on the '73 chassis without any issues?
Le Mans Master
Joined: Sep 2002
Posts: 5,236
Likes: 898
From: Myrtle Beach SC
No! 
The hardware and operating mechanism changed significantly from what is called the Omark tapered bolt to an energy absorbing system (EAS). As well, 73s used the metal spacers while in 75, rubber cushions were used for the body mounts. The NCRS 73-74 and 75-77 Tech manuals detail these 5 MPH safety features. But then if you cut, paste and weld, most anything is possible.
The hardware and operating mechanism changed significantly from what is called the Omark tapered bolt to an energy absorbing system (EAS). As well, 73s used the metal spacers while in 75, rubber cushions were used for the body mounts. The NCRS 73-74 and 75-77 Tech manuals detail these 5 MPH safety features. But then if you cut, paste and weld, most anything is possible.
Racer
Joined: Aug 2024
Posts: 276
Likes: 170
From: Pikes Peak region Colorado
2025 C3 of the Year Finalist - Modified
I put a 73 frame under my 74 some 32 years ago. If I remember correctly the front frame extension bolted up no problem and the rear bumper rebar I was able to bolt up with no problems. The thing I remember that was a big pain were the last two furthest rearward body mounts installing the bolts other than that it was really straightforward swap. I think I would verify that the rear body mounts are in the same location( I believe they should be the same) Hope this helps.
Last edited by Mr E's C3; Jan 17, 2025 at 02:52 PM. Reason: content
Burning Brakes
Joined: Oct 2013
Posts: 1,113
Likes: 520
From: McClellandtown, Pa.
No!
The hardware and operating mechanism changed significantly from what is called the Omark tapered bolt to an energy absorbing system (EAS). As well, 73s used the metal spacers while in 75, rubber cushions were used for the body mounts. The NCRS 73-74 and 75-77 Tech manuals detail these 5 MPH safety features. But then if you cut, paste and weld, most anything is possible.
The hardware and operating mechanism changed significantly from what is called the Omark tapered bolt to an energy absorbing system (EAS). As well, 73s used the metal spacers while in 75, rubber cushions were used for the body mounts. The NCRS 73-74 and 75-77 Tech manuals detail these 5 MPH safety features. But then if you cut, paste and weld, most anything is possible.
Just to clarify, in 1973 the body mounts were all the rubber cushion type. 1972 was the last year for the metal spacers. In my opinion using the 73 frame on a 74 would be much more manageable with a few modifications to the rear I guess as the one gentleman below remarked. However, like you I'm not sure it would be quite so easy to use on the '75 without a great deal of modifications. Even though we did discuss the differences in the front and rear bumper systems on the 73-74 vs. 75-77 in our TIM&JG revisions, I can't really say that it would help answer the OP's question. Going from the more rigid Omark Bolt systems of the 73-74 to the shock absorber/cushion type starting in 75 might be more challenging. JMO!
Again, like you said...anything is possible.
First photo below is the '73 - '82 Rubber body mount cushions.
Here are some more different images I thought I'd share for Green LT1. good luck with your project if you decide to proceed, please share your progress. Thanks!
72 and earlier C3 Body Mounts. Metal spacer used.
75 and later C3 rear shock absorber system
75 front bumper system! The cushion replaced the omark bolts to absorb the 5mph impact.
Last edited by Tooch1; Jan 18, 2025 at 08:04 PM.
Race Director
Joined: Mar 2016
Posts: 14,325
Likes: 8,129
From: Napa Valley California
The late/great David Howard, AllC34Me, was the frame guru when it came to swapping different frames with different bodies.
David posted a whole series of threads detailing what modifications, if any, and all the necessary parts that were needed to swap different year C3 frames with C3 year bodies.
Look up Davids past threads or Google search his Facebook series of threads.
David posted a whole series of threads detailing what modifications, if any, and all the necessary parts that were needed to swap different year C3 frames with C3 year bodies.
Look up Davids past threads or Google search his Facebook series of threads.
Team Owner
Joined: Jul 2004
Posts: 40,353
Likes: 787
From: Redondo Beach, California
Although the 73 is the first rubber bumper car, the frame is actually very similar to the 68L to 72 frames. So similar that when GM had C3 frames in their parts inventory, the 73 frame was used as the service replacement for 68 through 73 Corvettes!
How do I know? In 1980, I bought a new frame for the 69 I owned then. The 69 car as later stolen. Decades later, I decided to use this frame. I assumed it was a 69 frame and would directly fit the 70. A little problem mounting 1970 Corvette frame horns onto that frame. The bolt hole pattern was not exactly the same as my 68. I was not exactly the same as my old 70 frame?????? After a lot of calling around, no one knew what the problem was with my "69" frame until I relayed my oft told sad story to a Volunteer Vet tech. It was he that told me that buying a 69 frame from GM in 1980 meant that I would receive a 73 service frame.
How do I know? In 1980, I bought a new frame for the 69 I owned then. The 69 car as later stolen. Decades later, I decided to use this frame. I assumed it was a 69 frame and would directly fit the 70. A little problem mounting 1970 Corvette frame horns onto that frame. The bolt hole pattern was not exactly the same as my 68. I was not exactly the same as my old 70 frame?????? After a lot of calling around, no one knew what the problem was with my "69" frame until I relayed my oft told sad story to a Volunteer Vet tech. It was he that told me that buying a 69 frame from GM in 1980 meant that I would receive a 73 service frame.
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Melting Slicks
Joined: Jan 2012
Posts: 3,034
Likes: 503
From: myrtle beach sc
Army
As I stated above, my replacement frame said that it was for 68-74. It must be in 75 that the body mount brackets were lowered because of the rubber body mounts? Did they have thinner rubber body mounts in 73-74? Lou.