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Just to re-cap, I've been uncertain how much of the ACI 70-73 rear clip I should graft onto the back of my 79. This is the distance shown by line "A" in the picture below (the camera wasn't quite level so the picture is not exactly parallel to the ground). To match the rear end length of a factory 68-73 car I should use about 6 inches of it. As the width of the deck on the 70-73 ACI rear clip matches the width of the 79 deck at the 8 & 1/4 inch mark (point "A") I had been leaning to making my rear end longer than factory to minimize how much blending I need to do in order to get the two upper quarter panels to match and as well to allow additional room to fit part of the factory 79 crash bar. In thinking more about it and looking at the mockup picture below I realized the longer length probably won't work very well so I'm thinking very likely I'll be shortening the 70-73 ACI rear clip deck at point "A" to six inches even though this will make it narrower than the 79 rear deck where the graft line will be. Here's why:
Due to the downward sloping angle of the rear decks, using more of the 70-73 ACI rear clip not only lengthens the rear end of the finished car, it lowers the position of the ACI rear clip relative to the rear of the 79. This creates a couple of, in my opinion, unacceptable alignment problems with the join between the rear quarter panels of the 70-73 ACI rear clip and the 79 rear quarter panels.
On C3 Corvettes there is a horizontal character line at about the mid point of the quarter panel - "B" in the picture below on the 70-73 ACI rear clip and "C" on the 79. On the 68-73 rear quarter panels this character line is parallel to the ground. On the 78-82 cars (and perhaps the 74-77 ones?) that character line is not parallel to the ground but rather slopes upward slightly towards the rear of the car. When grafting on a 68-73 rear clip you need to blend these character lines together (so I think it best to use as much of the donor rear clip's quarter panels as possible) . In order to do that best the angle of character line "B" on the 70-73 rear clip needs to intersect the character line "C" on the 79 quarter panel at point "D". As you can see in the picture with the 70-73 ACI rear clip cut at the 8 & 1/4 inch mark (point "A") the position of the donor tail light area is lowered and the 70-73 "B" character line angle is too low to intersect the 79's "C" character line at point "D".
Similarly, with the lower position of the 70-73 ACI rear clip due to its increased length at point "A", the bottom of the 70-73 ACI quarter panel (point "E") does not line up with the bottom of the 79 quarter panel (point "F"). So, it appears to me at this time that I need to shorten the rear deck of the 70-73 ACI rear clip at point "A" to six inches to raise the entire 70-73 ACI rear clip relative to the back of the 79 even though this means the upper quarter panel width on the two rears won't match.
I'm feeling really fortunate I realized this before I proceeded with the longer ACI rear clip even though this is going to be a great deal more work than I anticipated. All the same I may cut the 70-73 ACI donor clip at the 7 inch mark and mock it up again to check once more rather than immediately cutting it at the 6 inch mark.
When we were doing R&D we often used the blue foam boards to mock up the changes and parts.
If I was unsure of the final look I wanted or the transition points I would trace the side profile on to the foam - you can cut it with an old electric kitchen turkey carving type knife or a hack saw blade ( blade makes a mess with little ball type dust , keep a shop vac handy). Fine tune the shape with sand paper 60 or 80 grit.
It's light and easy to shape. Home Depot has it, broken sheets are often vastly reduced.
Depending on the brand of the foam, Gorilla Glue, West System's epoxy etc will glue it together if you need thicker sections. Polyester resin eats it.
You can lay West Systems with cloth on it to make a mold and then cut the foam out. (West System's has a great website for their products and uses)
This may help give you the final look you desire, then trace that and make the cuts...
Last edited by BLUE1972; Mar 20, 2017 at 04:34 PM.
Question for you experienced auto body people. When I'm fiber glassing in the bonding seams do I need to sand all the way through the glue to the bonding strip as in at point "A" or if I hit the glue as at point "B" is that deep enough as the new glass will be at least as thick as the factory panels?
I also use the designing foam (as I call it) to create parts and check things when I need to...which was a great idea and may help her. What I use ...polyester resin does not eat it up. It is the foam like what florists use in artificial floral arrangements where they jamb the fake flowers in it to hold their position.
If anything I can add Priya. Is to get the rear clip where YOU want it and where it looks great to you. DO NOT worry about panels feature lines and all that...becasue THAT can be dealt with. And trying to keep your laminating to a minimum and that causes you to settle for a 'look' that just does not get you excited...then you are doing yourself an injustice.
Regardless if you have to laminate one inch seams or 5 inch seams....to me ...it is not that big of a deal when all that matters is the end result is what it NEEDS to be.
Making cuts in some areas a can relax the panels and allow them to be moved to lessen an off set panel. I have to do it quite often on new aftermarket hand laid parts.
Question for you experienced auto body people. When I'm fiber glassing in the bonding seams do I need to sand all the way through the glue to the bonding strip as in at point "A" or if I hit the glue as at point "B" is that deep enough as the new glass will be at least as thick as the factory panels?
Priya,
You can do as you wish...
BUT I do not laminate in the seam that you began to prep for filling. I simply apply some of the VPA and that is all. No need to waste the time or material in applying fiberglas resin and mat...but like I wrote...do as you wish.
You already know how stout the VPA is.
****EDIT****
I grind the adhesive down a bit...I widen the seam so when I am grinding I am going further out past the lines of where the panels are. SO..I basically prep the seam all the way to the top of the main body line at the top of the quarter panel and fender....tapering it as I go up and down. Then I will go down below the seam about 2 inches or so. I dish out the seams where the facotry glue was..and taper it further out to like where I just stated. I do not grind all the way down and find the bonding strip...no need for that. You want to go down at least 1/8"+ at the deepest point
What this does is allows a smooth gradual dish so when I go in with the VPA I have no sharp edges that I have to try to fill in. And because I am applying the VPA all the way to the top and below the actual area where the seam was....when I am done blocking the seam...the VPA can easily be 4 inches wide. And due to I dished out the factory adhesive...there will be no way for the factory seam to ever show up.
I'm going to fill the factory seams with fiberglass as the upper quarter panels on the 79 will be too wide to match the 70-73 ACI rear clip's upper quarter panels . I'll need to sand away the bonding strips on the inside of the 79's upper quarter panels so I can build up the thickness of them so I can sand away the exterior surface until its narrow enough to match the upper quarter panels on the donor 70-73 ACI rear clip. That way when I sand away the bonding strips on the 79 the quarter panel and deck panels won't fall apart.
I have no technical skill to add here, but I want to say Priya, you're an inspiration to us all who have dreams of taking a plunge like this. It may seem like more hard work than fun right now, but a lot of people are pulling for you and genuinely interested in your project! Keep up your energy, and I look forward to seeing your result!
Wow Priya - your Vette is going to be stunning! It's fun to follow your build and see your challenges and accomplishments. Keep up the great work - can't wait to see it finished.
I glassed in the bonding seams yesterday. It was my first time working with West systems epoxy resin. Its no fun at all. Its about the thickness of corn syrup and doesn't like to soak into the fiberglass mat when you apply it to the surface of the mat on the car as I do. As usual I didn't use enough hardener and 18 hours later the resin isn't completely hard yet.
To make the resin easier to work with I thinned it with acetone which may have not been the solution to the extra thick resin. Although I wiped off the runs when I left the garage more runs appeared later on - what a mess! Also, as shown in the picture below it looks as though enough resin ran out of the mat so that it is insufficiently saturated near the top of the fiberglass work.
I went out to check if the bonding seams were hard enough to sand. They weren't but I was pleased to find out the resin was still soft enough that I was able to remove the runs with a razor blade. So, that saves a bit of effort down the road.
It seems you chose to laminate up your seams using the West Systems resin.
IF your resin/hardener are cold...you should not use it due it it will be thick as all get out.
Set the can in the sun to warm it up and you will find the viscosity will change A LOT and be much thinner.
Hopefully you contacted West Systems and they said it was OK to thin it with acetone. You are dealing with an epoxy resin and not a polyester...which the acetone could effect it can cause it not never harden fully and have to be all done over again.
I will keep the rest of my thoughts/comments to myself.
OH oh , I had some polyester do that to me the other day, It was thinner than normal in the can but I used it anyway (my mistake there ). about the top 3rd ran out , I ground it all out and started again, but used a heat gun to set it quicker ,you can see it pooling by the self tapper screw,
I don't like using a heat gun to speed it up , I think its better to let it go naturally, my point is I really hope yours does go off , but your going to have to grind at least that top part back !
No big deal , these cars are 3 steps forward and 2 back all the time
Last edited by bazza77; Mar 23, 2017 at 07:46 PM.
Reason: was it 3 forward and 2 back or 2 forward and 3 back ?
I went out to check if the bonding seams were hard enough to sand. They weren't but I was pleased to find out the resin was still soft enough that I was able to remove the runs with a razor blade. So, that saves a bit of effort down the road.
Hopefully tomorrow its hard enough to sand.
Priya, I was curious as to why you did the seams that way instead of using VPA (vette panel adhesive). I am no expert body guy so I am not a know it all by no means. Just curious and I guess there are many ways to do things. All good!
RVZIO
Priya, I was curious as to why you did the seams that way instead of using VPA (vette panel adhesive). I am no expert body guy so I am not a know it all by no means. Just curious and I guess there are many ways to do things. All good!
While the upper quarter panels on the 70-73 ACI rear clip and the 79 are very similar they are a little rounder on the 79 where the bonding seams are. To blend them together I will need to sand away the bonding strip from the inside of the 79 quarter panel and fill the inside of the 79 quarter panel with fiberglass so I can remove the roundness on the outside of the 79 upper quarter panel to match the upper quarter on the ACI rear clip. I fiberglassed the seams together so that when I remove the bonding strip from the inside of the 79 quarter panel the quarter panel won't fall off the upper deck panel.
OH oh , I had some polyester do that to me the other day, It was thinner than normal in the can but I used it anyway (my mistake there ). about the top 3rd ran out , I ground it all out and started again, but used a heat gun to set it quicker ,you can see it pooling by the self tapper screw,
I don't like using a heat gun to speed it up , I think its better to let it go naturally, my point is I really hope yours does go off , but your going to have to grind at least that top part back !
No big deal , these cars are 3 steps forward and 2 back all the time
Yes, I'll be grinding off the top part of the work I did and re-glassing it. I think its better too to let it harden naturally. Although I used the heat gun on it for a while today I didn't get it any warmer than was comfortable to the touch. I'm pretty sure its going to harden the rest of the way, it was firm to the touch and dry to the touch except in some areas at the edge of the lamination.
Yes, I'll be grinding off the top part of the work I did and re-glassing it. I think its better too to let it harden naturally. Although I used the heat gun on it for a while today I didn't get it any warmer than was comfortable to the touch. I'm pretty sure its going to harden the rest of the way, it was firm to the touch and dry to the touch except in some areas at the edge of the lamination.
Phew , that's good news , maybe leave it for a couple of days ,go on to another part or just close the shed and get away from it altogether
It's fun to follow your build and see your challenges and accomplishments. Keep up the great work - can't wait to see it finished. 
