I tried to fit the smaller piece of the 79's crash bar today with the 70-73 ACI rear clip mocked up into place , it wouldn't fit. I could probably sneak it in if it weren't for the bracket for lowering the spare tire shown below outlined in yellow:

 

I would remove this bracket that is in the yellow square...the see if the impact bar will work. Then I would look and see what I would have to do to get the spare tire bracket to work...even if I had to re-design it entirely.

The one good thing is the black plastic upper portion of the spare tire carrier is a good template to use to see what might need to be done.

And obviously I would remove the taillight support housings and the extruded aluminum center support off the impact bar.

If you can get this impact bar installed...I feel it would be a very good thing for safety as I had mentioned in a previous post when this subject was discussed.

DUB

 

I hope these are the angles you're looking for Dub.

Passenger side:








Driver's side:







The upper deck of the 79 is pretty much flat at the join while the upper deck of the 70-73 ACI rear clip has a convex curve at the join. The wood clamps bring the two pretty close to a match but the edge on the 70-73 ACI rear clip where the quarter panels meet the upper deck is still a little lower than the same spot on the 79 than it should be. I need to figure out a way to raise the outer sides of the 70-73 ACI rear clip an eighth of an inch or so more when all the wood clamps are in place. You can see the difference in the picture below when I remove the wood clamp holding this edge together:


The upper quarters on the 79 are a little wider than the upper quarters on the 70-73 ACI rear clip and the lower quarters on the 79 are a little narrower than lower quarters on the 70-73 ACI rear clip. The horizontal mid quarter panel character line is parallel to the ground on the 70-73 ACI rear clip but rises to the rear on the 79's quarter panel. I have to reshape the 79's quarter panels to match this character line to the character line on the 70-73 ACI rear clip so I'm thinking of cutting out the area outlined in red on the 79's rear quarters and pulling the 79 upper quarter panels in a bit and pushing the 79's lower quarter panels out at bit to get the two to match. Then I'll layer in mat and resin between them and sand the shape to produce a mid quarter panel character line that matches the one on the 70-73 ACI rear clip. I figure if I don't do this I have to add mat and resin to the inside of the 79's quarter panel at the mid quarter character line and then sand down the mid quarter panel character line on the outside of the 79 quarter panel anyway and will likely sand through the original SMC anyway:



Pulling in the upper quarters and pushing out the lower quarters on the 79 will line up the upper an lower quarter panels nicely but the area shown in blue above will still be too wide on the 79. I'm thinking I'll layer fiberglass mat and resin in the inside of the 79 quarter panel at this point, then shave down the outside of the quarter at that point. I may also add mat and resin to the outer edge of the quarter panel at this point on the 70-73 ACI rear clip to blend the two areas together.

 

I have the 79 crash bar completely dismantled. there are two steel sections that go across the width of the rear of the car that bolt together. If anything can fit it will be just one of these long steel sections.

 

In my interest of grasping something,
i am gonna side step a little,
SawThere is a lot of furor over the inner structures that were there for safety as of 1979 standards, they would be different in todays standards,
I recall your orginal plan was keep all the 79 safety stuff under the chrome bumper conversion, and as building has gone forward that has turned out to be impossible, So since its a 68-73 rear conversion isnt what they had for safety good enough since its a custom, or are 68-73s rears antiquated death traps?
Im interested in the feedback from the out of box home builder point of view, your new plans as the build progressed, i fully realize a shop would be far too paranoid of lawsuits if they changed even one little thing from the factory way,
But yeah, customs are trade offs,

Back to track i would be super curious what doorgunner or don think of the fit now and which way to progress forward,
It looks super good, im more and more excited and motivated.

 

I suppose if I had bought a 69 I'd have been satisfied with the structure as it was made back then. Having seen what is in the 79 though it seems very flimsy compared to that so I'd prefer to have a better safety structure in a chrome bumper car.

Having said that I'm not sure its in the cards for me to rework the spare tire carrier. This is already taking a lot longer than I had planned, hubby is upset about me monopolizing his garage and I'm not sure how much I've got in me to keep adding work, in particular fabrication work to get some of the 79 crash bar in place. I"m already feeling stretched pretty thin to get the rear body work done and the brackets for the rear bumpers adapted to the 79 rear frame crossmember.

I'll think about it some more.

 

I fully realize the stress you are under,
The outside is close, very close if it were me and my car i would place all my focus on that outside look get that done,

Then after the outside is good i would figure out how to make myself happy with inner structure, stock 79 inner is gone, forget it but no reason you can't work up something you feel is safe likely way safer than my 69 stock,

I would likely talk to my buddies who were racers of c3s for ideas on inner structures,

On the clip, do you believe you have trimmed out as far as you will where the top meets the deck?

 

Yes. Its still an inch or perhaps an inch and a half longer than a factory 68-73 rear but I think the overall fit is pretty good and shortening it more would result in a poor fit on the quarter panels due to narrowing further the 70-73 ACI rear clip so I think given that it can not be trimmed to fit perfectly I have the best all around compromise on the various dimensions.

 

Rookie here: Like you/Bats/Dub/others have said---concentrate on the exterior/aim for the best fit...don't let an extra inch bother you/I won't tell if you won't tell.

You'll feel much better about the project once the clip is fiberglassed into place........MUCH better!

 

It'll be our secret

Thanks, I'm sure you're right!

 

Priya,
Your photos were a great help BUT....I still need two more.

The 8th photo in POST #623 is close to what I need but still not quite. I need to see how the top quarter panel line flows back to the ACI clip...and then HOW the top line on the ACI looks when it is up against your rear clip. So this view may need to be from up high.. kinda looking down on it at an angle so I can see teh flow. Removing the paint on your body so it will show up as the highest point on that line would be helpful to show up in the photo and them taking a Sharpie and drawing a line on the top line of the ACI clip.

AS for you doing anything with your impact bar....I am leavign that up to you. I am not paranoid about this area....I just know that I would HAVE to deal with it. That is a REALITY I have to deal with. I wish I could do what a lot of at home customizers can do on their own cars....but I can not.

I do not live where you live and know the rule, guideline or regulations...but you might want to ask yourself a question. DO you feel that your insurance company would cover you if your left out the impact bar...(that was there for a reason for that model year)...and for some unforeseen incident...the passenger riding with you who is unknowingly in a car that has been....altered in regards to safety structure... got hurt. And it was found that due to the lack of SUFFICIENT approved/tested safety structure being installed??? I HAVE seen scenarios like this over the decades of me working on cars. It does not happen often...but I can think of three right off the top of my head.

If you or anyone else think I am paranoid or crazy...so be it. But what may shock you is you call your insurance company and throw them a hypothetical scenario and ask them if you would be covered or not. See what they say.

I can understand that you have taken on a lot and you ARE doing a very good job...just in case you feel you are not.. WELL..you ARE doing a very good job. And even with guys like myself when we have to custom modify parts to work...that is the challenge.... to get them to fit and function. Parts being put on and taken off countless times until SUCCESS.

DUB

 

I dont feel well and bored not a great combo for a bat early on a Saturday eve,

If i am grasping this situation its being stated any and i do mean any modifacation to a cars factory safety structure would place it into this area that could end up with all kinds of horrors , insurance not coming through, law suits, dogs and cats living together, chaos of biblical proportions,

So the easy answer is for the love of God dont change one little thing about the factory safety structure of a car, if you do all hope is gone.

Too late in this case, factory safety structures have been changed,

So is anyone actually suggesting in any way to abandon the project...discard it?

If that answer is no, that is stupid i would never suggest abandoning the project then why not harp more on helping getting the outside look correct and waste less time on lectures about factory safety structures, worry about inner safety structure later on, you must admit the whole subject of not changing inner safety structure on projects like this one has been beaten to death, i believe people do get it....

So why not put that effort into getting the outside looking good, i would find that far more positive and motivating to the builder, if i was in that boat.

 

if i understand correctly , insurance co's and other experts are ok with doubling , tripling or even quadrupling horsepower , are ok with ripping off the entire brake systems and changing to aftermarket , ripping out steering columns and steering boxes and going after market , changing suspension components to aftermarket or even changing the style of suspension, changing wheel offsets , alignment specs and almost every other designed in aspect of the car , 90% of it is SAFETY related ,but the line gets drawn at an antiquated component that was marginally effective for what it was designed to do almost 40 years ago....do yourself a favor and look at what that particular component was designed and mandated to do as of model year 1979 and you will find it is a whole lot of junk hanging on the back of the car for not very much , fwiw every fiberglass bumper cover that has ever been put on over that mostrosity by anyone has defeated the purpose that it was designed for.

 

Dub, I'll get some more pictures for you in the next couple of days. I'm not entirely clear on what you mean but will hopefully come up with something that helps you out.

 

Priya,
I will look for the photos.

Sorry Priya...but I have to.

It seems that some people have to express their views...in such a manner...that they still cannot grasp the IMPORTANCE of impact bars, etc. It seems that they will never get it and in doing so...they come across quite foolish due to their method of mocking an area that they feel is pointless to discuss. I love it that when a part is removed...like the outer shocks for the impact bar..are there for a specific MPH impact standard...that if they are removed ..ALL IS LOST AND NOW THE CAR IS WORTHLESS....is a JOKE. Obviously they have no clue on how to handle that. BUT....that is their choice. But I guarantee that people who can not understand it and can only pick at it and find fault in what is being discussed want to go to a part of this modification that will cover this area for good and deal with it due to more than likely...would not know how to deal with it...simply because they feel it is not worth their time. It is CLEARLY...their way of thinking...which we can all see....we differ on this GREATLY.

I am commenting on its importance BECAUSE it IS important...and I will leave it up to 'Priya' to decide. It is not like I had not made my thoughts on this quite clear. So any decision to the contrary...may or may not come back and haunt her. So it can not be said that it was not discussed.

AS for components that are there for IMPACT ISSUES...which impact components area SAFETY component...if people want to group them up to make a point....I guess that is
how they see it....but impact bars have nothing to do with steering, brakes or anything else. it is in its own sub-category in the SAFETY COMPONENTS of the car. ...people can do as they wish.

And honestly....commenting on how changing out a urethane bumper cover for a fiberglass one is really stretching it...because anybody in the paint and body industry KNOWS that the urethane covers offer basically nothing to impact resistance...and they are
a 'throw away and replace part' when they get damaged bad enough...and they are simply their for styling. ALL of what is important is BEHIND that urethane cover.

For those people who want to comment on issues of importance...I would make a suggestion that you get an education on it before you comment on something it is obvious you know very little about. Do as much work for insurance companies where the cars are often times THOROUGHLY inspected....THAT will make you 'see the light'. The insurance companies are VERY TOUCHY in certain areas of a car...and IMPACT areas ARE ONE of them.

DUB

 

United States[edit]
The United States has focused on protecting consumers from repair costs, using government legislation.

First standards 1971[edit]
71 Dart Front Bumper L.jpg 74 Valiant Front Bumper.jpg
71 Dart Rear Bumper.jpg 74 Valiant Rear Bumper.jpg
Front and rear bumpers on Chrysler A platform cars before (left, 1971) and after (right, 1974) the US 5-mph bumper standard took effect. The 1974 bumpers are larger, heavier, and mounted farther away from the body, and they no longer contain the taillamps.
In 1971, the US National Highway Traffic Safety Administration (NHTSA) issued the country's first regulation applicable to passenger car bumpers.[why?] Federal Motor Vehicle Safety Standard No. 215 (FMVSS 215), "Exterior Protection," took effect on 1 September 1972—when most automakers would begin producing their model year 1973 vehicles. The standard prohibited functional damage to specified safety-related components such as headlamps and fuel system components when the vehicle is subjected to barrier crash tests at 5 miles per hour (8 km/h) for front and 2.5 mph (4 km/h) for rear bumper systems.[34] The requirements effectively eliminated automobile bumpers designs that featured integral automotive lighting components such as tail lamps.

In October 1972, the US Congress enacted the Motor Vehicle Information and Cost Saving Act (MVICS), which required NHTSA to issue a bumper standard that yields the "maximum feasible reduction of cost to the public and to the consumer".[35] Factors considered included the costs and benefits of implementation, the standard's effect on insurance costs and legal fees, savings in consumer time and inconvenience, as well as health and safety considerations.

The 1973 model year passenger cars sold in the US used a variety designs. They ranged from non-dynamic versions with solid rubber guards, to "recoverable" designs with oil and nitrogen filled telescoping shock-absorbers.[36]

The standards were further tightened for the 1974 model year passenger cars, with standardized height front and rear bumpers that could take angle impacts at 5-mile-per-hour (8 km/h) with no damage to the car's lights, safety equipment, and engine. There was no provision in the law for consumers to 'opt-out' of this protection.

Regulatory effect on design[edit]
Cars for the US market were equipped with bulky, massive, heavy, protruding bumpers to comply with the 5-mile-per-hour bumper standard in effect from 1973 to 1982.[37] This often meant additional overall vehicle length, as well as new front and rear designs to incorporate the stronger energy absorbing bumpers.[38] Passenger cars featured gap-concealing flexible filler panels between the bumpers and the car's bodywork causing them to have a "massive, blockish look".[39] A notable exception that year was the new AMC Matador coupe that featured "free standing" bumpers with rubber gaiters alone to conceal the retractable shock absorbers.[39]

US (left) and rest-of-world (right)
1979 Mercedes 300SD 116.120.jpg Mercedes Benz W116 aka 280SE in Belgium.jpg
BMW-535is.jpg BMW 525i E28 01.jpg
Lamborghini Countach US spec 5000QV.jpg Lamborghini Countach (8014529631).jpg
Front bumpers on Mercedes-Benz W116 (top), BMW E28 5-series (middle), Lamborghini Countach (bottom): The US bumpers are more massive and protrude farther from the bodywork.
All 'domestic' cars had this feature, and imported vehicles were also required to comply. With very few exceptions, such as Volvo 240 and Rolls-Royce Silver Shadow, foreign manufacturers only sold this feature in markets that mandated it, the U.S. and Canada, so 'rest-of-the-world' models had a notably distinct appearance.

US bumper height requirements effectively made some models, such as the Citroën SM, suddenly ineligible for importation to the United States. Unlike international safety regulations, U.S. regulations were written without provision for hydropneumatic suspension.

Zero-damage standards 1976[edit]
The requirements promulgated under MVICS were consolidated with the requirements of Federal Motor Vehicle Safety Standard Number 215 (FMVSS 215, "Exterior Protection of Vehicles") and promulgated in March 1976. This new bumper standard was placed in the United States Code of Federal Regulations at 49 CFR 581, separate from the Federal Motor Vehicle Safety Standards at 49CFR571. The new requirements, applicable to 1979-model year passenger cars, were called the "Phase I" standard. At the same time, a zero-damage requirement, "Phase II", was enacted for bumper systems on 1980 and newer cars. The most rigorous requirements applied to 1980 through 1982 model vehicles; 5 miles per hour (8 km/h) front and rear barrier and pendulum crash tests were required, and no damage was allowed to the bumper beyond a 3⁄8 in (10 mm) dent and 3⁄4 in (19 mm) displacement from the bumper's original position.[40]


Freestanding 5-mph shock-absorbing zero-damage bumper, AMC Matador coupe
All-wheel-drive "cross-over" cars such as the AMC Eagle were classified as multi-purpose vehicle or trucks, and thus exempt from the passenger car bumper standards

 

not a stretch at all...the impact bars sole job in life was to prevent body damage , unless its covered with something flexible it won't be capable of doing what it was designed to do. unless you have some magic fiberglass cover it will suffer damage on impact.
if you don't understand the point i was trying to make , so be it.
between the two of us we have taken priyas thread as far off track as it needs to go , you have made your thoughts on this topic abundantly clear on this and other threads more times than i can count.... implying that anyone that did not see it your way was and i quote " an idiot" in another thread. i fell for your relentless harping on the subject so i am as guilty as you. i am done , i wish priya the best with her project and hope you are man enough to let this topic die a quick and quite death. if you feel otherwise start another thread , let priya proceed in her project without any more of this nonsence

 

I got a "not too far fetched" so I must be moving up in the world.

 

So your viewpoint is that large steel double C shaped bumper, mounted to a larger boxed section of the rear frame by two large steel dampers, is nothing but junk COMPARED to the silly inadequate chrome bumpers attached with small rods to the small rear crossmember of the earlier models are EQUAL in terms of crash protection.....I think anyone with common sense would disagree. What you call junk would clearly absorb rear impact damage and slow down the damage into the fuel tank / fire source. It may be heavy and ugly, but it does serve a purpose.

Now, with that being said, its anyone's choice to take the risks that puts you in, both legally, and more importantly from a safety standpoint if you choose to operate without it. I think Dub is just trying to point out a reality. I am no safety advocate, if I were, I certainly would not own or drive a C3 Corvette that is many times more unsafe than any modern vehicle, but I don't have any misgivings about it. But I also don't try to pretend that early C3 bumpers were anything more than bling. By 74 and later, there was a mandate to actually equip the car with real bumper protection. It clearly provides more than just body damage protection, no matter what the legal jargon attached above says.

Just as in aviation, most safety rules are written in blood.

PRIYA, sorry your thread is getting hijacked, but I really like your mod plans, as well as some others doing the same, and I only wish there was a way to keep some of the bumper protection these later cars had, and still have the cosmetic appearance of the early models. Maybe what Dub is suggesting is he has ideas on adding back in some amount of bumper protection.

 

Please, enough talk about the bumpers already.

If I thought I could get part of the 79's crash bar in place with no more than 10 hours work I'd be happy to do it but I don't really have any experience in fabrication and I could easily see this taking me 40 hours to re-work the spare tire assembly, crash bar, bumper brackets etc. I'm already feeling overwhelmed by the thought of having to adapt the 68-73 bumper brackets to the 79 frame rear cross-member.

I'm not the most driven person in the world and I don't want to stretch this out to where I give up because its too much. This is already taking much longer than I planned and Hubby is grumbling that I'm monopolizing his garage. I'm well aware of the risks I take without the 79 safety bumper in place and I don't take leaving it out lightly. Having said that I recognize that I also am only averaging 600- 1000 miles a year on the car so its not the same risk I'd be taking if I was driving the car 20,000 miles a year like the average American driver.

If I had to do this all over again and knew what I was in for I would have just put the pace car spoilers on the car and left it at that. But there's no turning back now so let's not dwell on this.