I'm in the process of build my own C3 rear bumper conversion in fiberglass, how very, there are a few measurements I'm in need of and I'm hoping someone out there may have the numbers I'm looking for.
Below are some pics of my bumper and I have put lines where I need the measurements. I figure It would be easier to build one, this way I have a plug for when I mess up the first dozen times.
I didn't realize the amount of time I had put into this bumper till my wife started to yell at me, so I need to get this done to shut her up. Thanks

 

Did you know there is already a product on the market? May be better off buying one of those than trying to build one.

 

I seen one about 2 months ago but I'm unable to find it now. If I remember correctly it was $900 US and I live in Canada, so I would have the exchange rate plus the duty plus the shipping, so that brings the cost to high for me. There was also a guy on Facebook but Im unable to find him. If I make my own plug then I have the ability to alter the design if I wish, it also allows me to mess up a few times

 

Gotcha.

 

I can't help with the measurements...just be sure you want dual exhausts exiting the rear. I changed to sidepipes and had to fill in the dual exhaust openings. It would save you alot of time in fabricating openings.

 

I'm thinking of going from round to rectangle, but I'm also thinking of using removable plates for the plug in case I change my mind. Once I have the plug its just a matter of fiberglassing a new bumper.

 

Are you sure you will like the look? I have seen a few that bolt on, and they don't really flow too well. Definitely don't really look exactly like a '68-'73.

 

This is a fantastic idea, one that I considered doing. I think you could market it and sell, if you wanted to make the effort. I like what you are doing far better than the previously mentioned product, which had some exxagerated lines, and some poor fitment issues to the peaks on the sides. He tried to incorporate the chrome bumpers, but I like what you are doing better.

What it needs to be is a very exact match to the original C3 design, and flow well into the rubber bumper rear fender lines. Ideally you would want to be able to simply remove the original rubber bumper cover, and bolt this on to the same mounting flange. As I said, the previous product did NOT flow well into the peaks on the side of the rear fenders, and created awkward looking transition. If you could make this to fix that, it would be a great improvement. I also would not want those cutouts for the exhaust, which mimic the 68-69 design, so that I could continue to use my turn down, under the bumper, mufflers and tips. AND.....I would not want those rectangles below the lights, which I suspect are for reverse lights.

I think you will find that the rear fender side peak lines are at a different location and angle than the early chrome bumper C3 rear fender lines.....so I know there is a way to make it work where the lines flow properly back....but you have to make this happen with you plug.

Lastly,......IF this conversion requires that I remove the heavy steel ACTUAL bumper underneath, its a no-go for me. If I were to design this, I would make it work to allow keeping the actual real bumper underneath this fiberglass cover......or fabricating some type of real steel bumper underneath. I know early C3 Corvettes had cosmetic chrome bumpers, but they were nothing more than cosmetic jokes....attached with worthless 1/4 inch rods to the frame. I simply am not interested in having NO real protection considering the location of the fuel tank. Not interested in dying in a fire.

I really like the drawings you attached, and I think you have done a great job at duplicating the early C3 look....and if this could be made as a bolt on conversion to the rubber bumper cars, with the limitations I wrote above, I myself would be very interested, assuming a reasonable price.

That all being said,........I like the look of the rubber bumper rear end.....the designers did a great job at creating the styling connection of the rear light cutouts to the speedo / tach cutouts on the dash. And while I do like the back end of the early cars better,.....I don't share the commonly stated hatred for the rubber bumper back end. I think they are different, but both look great.

I hope you keep us up to date on this........

 

^^^I agree with what he said.^^^
To make it look right, I (think) the inner steel bumper has to go. If you can make the 'glass, I can fabricate a rear inner bumper probably pretty easily. I'd buy one too, and make you or anyone else a bumper.

 

I will add that there is an unfortunate reality, that if you make this fit your car perfectly......it most likely will not fit anyone elses car perfectly. The cars were hand built, and there can be wide variations in where the fenders are mounted to the rear top part of the car, including where the fender peak lines are. Its all fixable with filler and or cutting,.....but its a reality. When I had my car painted, I made the huge mistake of listening to the painter and bought Trueflex bumpers.......and despite their "flexibility"......there was still lots of filler work required. AND....the unfortunate downside to the FLEX type bumpers is that they are almost as weak, thin and wavy as the original RUBBER bumpers. SO.....make sure you make these bumpers very THICK....with standard NON FLEX resin.....so they have the same rigidity and strength as the fiberglass the rest of the car is made of......no reason to have a beautiful WAVE FREE body.....with bumpers that look like crap.

The truth is, the reality is......ANY fiberglass bumper made for a production C3 will most likely need extensive work in filling and possibly cutting to match each individual car. I would accept that if someone could make a good conversion piece like you are suggesting. My front Trueflex bumper will be someday "worked on" to make it less wavy, and more like the rest of the car.

 

Thanks for all the suggestions. many I have all ready considered like, the rear bumper support, from where I see it, its a MUST to protect the rear of the car, so my intention is the make the bumper (bolt on) then, turn my sights the the support. As for the reverse lights they will be part of the main lights. Followed by the body lines, they MUST follow through to the bumper and fade off there. As for the exhaust cut outs, My intention is to have a plug that can fit in the exhaust cut outs if I choose I don't like the look.
As Torqued Off stated, and I must agree with him. The ones on line don't seem to have the right lines or fitment. I'm not trying to replicate the 68-73, if I was it would have the chrome bumpers, I'm just trying to make something that I like.

 

You have just pointed out another reason why I'm making my own... will it cost more. HELL YES but at the end of the day, its something I made, and unique to my car

 

Thanks for the offer, I appreciate it, but I have a LONG way to go with making it. First it will be a 3D print, then fitment to the car, then shaping to get the body lines I'm looking for, then make the plug, followed by the fiberglass bumper, and start the hole process over again to refine it.

 

been down the road you are going , i pulled a mold off the rear of a 71 to get the top 1/3 to 1/2 of the tail and the critical shape of the tail lights and ducktail. after months of shaping , reshaping sculpting and fine tuning a few things became obvious ( at least to me ) . i was building the plug on the rear of a 77 and was lucky enough to have my 72 to compare them side by side. if the tail was long enough to fit over the existing conglomeration at the rear , it looked real bad , if the angle of the duck tail was off much it looked bad , there were a lot of things that need to be massaged . the rear fenders of the chrome cars are quite a bit different than the rubber cars and as easy as it sounds to make the transition from one to the other , to make it a true bolt on some compromises will be in order. i think what i made looked pretty good , but you will find out everyone is a critic as well as a safety expert. i wish you well and believe me its doable

 

What are the small rectangular recesses in the lower portion for? Reflectors?

 

I am not a "critic"....I am simply pointing out the reality of the discontinuity in the lines. If that makes me a critic by your definition, then so be it, but beyond that,....its a simple fact that is far from subtle, and is very obvious. AND, I am not a "safety expert" either....it only takes common sense...expertise is not required, .but again, facts show that removing the actual REAL bumper on the back of a rubber bumper car clearly makes the car less safe. Again....simple truths. Nobody has to like it, or agree with it, but on a forum, people need to know ALL the points about this type of conversion. Anyone can then make an educated decision and sacrifice good flowing body lines and "safety" issues if they choose to do so. But trying to minimize these realities is pointless, and just sounds like sour grapes and defensive. No need for that.

Your mod is at least better than no mods.....if someone hates the rubber bumper look. And frankly, I like what you did, with the exeptions I listed above. But they are NOT compromises I am personally willing to make on my car.......I am not a rubber bumper rear end hater like so many. In fact, I think it looks pretty damn good....not as good as early C3 rear ends, but still very stylish and shows great design by the design team at Chevrolet....no matter what people proclaim on a forum. Of course, thats my opinion....which everyone has. Its personal taste...not a fact or is open to question or votes. Even if 90% of the population prefers the early design better....it means nothing if you like the later design. Its not a right or wrong equation.

And so when the OP posted this thread,....it opens up the possibility of an option that would be acceptable to me. No, its not easy. But it can be done. I could do it. Will I? Maybe.....but I have more important things to do right now.

 

I have come to the conclusion that it would be easier to remove the existing 'glass and put on '68-'73 'glass. When you throw into the mix, a huge 3D printed pattern, making a mold you will only use once, and it still comes out looking "wonky"...

No offence to the guys that have the bolt on conversion and like it, to each his own.

 

Yes,....this may be true. I know Harborvette, Erie PA has done it, and they simply replaced the entire rear clip, and made whatever mods you need to make on the frame, which could be simply welding on a early C3 rear frame piece. David Howard had shown that is not a huge project if you are in the body off stage. Anything is possible with enough focus...and money.

I like what the OP is starting with....

 

The other design challenge is how the rubber bumper cars have those fake bumper extensions molded in......which actually start on the bottom of the rear fenders. Those would have to be removed from the rear fenders and not sure how that would affect the flow of the lower fender line. Its complicated for sure. Some would say the easiest solution is to sell the rubber bumper car, and buy an early model.....but that comes with a bunch of compromises as well. Chevy improved the cars every single year in many ways.

I am a fan of rubber bumper cars, so its not a big compromise for me to own one, and I don't necessarily feel the need to try to turn it into a early model. Embracing the car you have is the absolute easiest solution, and finding the beauty that does exist there.

Of course, I love them all.....so its easy for me.

 

Well, I don't know quite what to say... I've had a lot of good answers, along with good questions and concerns. But I didn't post it, to see fellow members arguing. There is no right or wrong, when it comes to answers, question, concerns or debates. This is a car that took me 30 plus years to be able to get, and I have a 5 year program to get it ready to hand over to my son as I will be unable to enjoy the fruits of my labor.

The CAD that I have done is just a ruff interpretation of my final design. Because it was done CAD all the measurement are accurate to allow me to bolt it right on. The 3D print will consist of 26 smaller prints (3-4 days) that will be connected together to form the whole bumper which will be installed on the car for refinement. From that point I will create a plug while it is on the car. then create the the bumper from there.
The main steel bumper support will be modified to fit under the new bumper.
I have wasted more time watching tv then doing something constructful.
f you don't push yourself, how will you ever know what you are capable of.