Dennis, I don't have much experience doing fiberglass work but I do know the factory fiberglass was supposed to be 1/10 of an inch thick. I suppose in theory if your join was this thick it would be okay but I would think one would want it an 1/8 inch thick or a little more. The way I plan on doing it is layering on the mat and resin on the inside of the join where it won't be seen and leave it a little thicker than the factory panels at that point. On the exterior of the join where it is seen taper the two panels where they come together down to the mat and resin on the inside. Then add some mat and resin to the outside visible surface. Sand that down a little past to a little lower than the level of the surrounding panels and then fill the low area with vette panel adhesive/filler. Then block down the Vette panel adhesive/filler until it is at the same level as the untouched panels you've joined together. That way there is no bulge or mound on the exterior visible surface but there is a bit of one on the interior surface to provide strength.

 

You got mail..

 

OBVIOUSLY YOU CAN NOT let this go.

Things were fine here until you jump in and have your way of commenting on what you feel is not important and should be overlooked...which is fine if this was your thread....but it is not....then the name calling...once again...emotions overriding ones intellect. ..thin this post where you obviously did not see my post #649 where I DID comment on the photos.

Gets your facts straight.... and I fell the same way about YOU as you do for me.

PERFECT.....as so much for you 'saying' that you do not have much fiberglass experience.

Deciding on cutting both panels is up to you so you can see how the flow of the body is moved and if it is optically pleasing to you. I can say that laminating areas that are upside down will take a bit of time due to you do not want to apply to many layers due to it can fall off. I know that some people may use masking tape to hold up the area...but I prefer to do it in stages.

I gave it some thought..and I know it is up to you. But due to the fact that I have done this for a long long time..I can see what the end result will look like before I begin. Possibly you have that ability now..I do not know. But...back in the day when I was starting out and had not yet acquired that ability. In cases like this....I would take masking tape and cover the area to close off all openings or gaps so the bondo would not go through them. Then...using super cheap bondo..I would apply the bondo on the tape and shape it and see if it would look good. Get it really close and shoot some cheap primer on it so I could see it better because it is one color. If it did..I could remove the bondo due to it being on tape and do what I was thinking. This way...this idea may make it so you do not have to cut the factory quarter...because you can shape the area on the ACI part...and thus...this would tell you that you would only have to cut the ACI part.

And this is why I am thankful that you posted those photos. For me...getting the top quarter lines is not that big of a deal...but it has to do with the flow of the factory quarter where it into the ACI clip and how that looks.

DUB

 

Can you?

 

Thanks for the suggestion, I'll give this some thought.

 

It is worth a try if you can not envision the end result. I know it adds more time and $$$ to a project...but sometimes spending time in a direction that can aid in completing a project is worth while.....
OR...
Laminate it up and even if you have to cut a lamination and do it again...it still gets you to the end of the project.

DUB

 

A FEW THOUGHTS: the ends of the panels should be tapered inward to give more bonding surface to the filler patch. I liked a 15 to 25 degree taper to maximize the bonding and prevent joint failure. Thin part is the inside surface.

If I remember correctly West Systems recommends a 20 to 45 (max) (stress travels at a 45 degree angle approximately) degree taper of the panel thickness, as does most glass suppliers. I found the more gentle taper angle to be superior in tension and bending tests. It also helps negate the difference in stiffness between the different fiberglass panels.

If you slit the panels, I would drill a round hole at the end of the slit to prevent the slit from spreading.

When I was on the ASTM committee writing the specs we all agreed that the lower the angle the better the bond, especially in high stress and vibration situations.

Again just some thoughts... good work .. the end will be great..

 

I still can not grasp WHY some feel that a hole needs to be drilled in fiberglass or SMC.

I DO agree with drilling hole in steel or aluminum where the metal has a tear in it and it can move and a person wants to stop it from creeping.

But in this scenario...where neither panel is going to be moving/flexing due where the cuts are being made...drilling a hole that is going to be filled in just does not make any sense.

BUT...a person can do what they want...and I have never drilled a hole and as of yet..I have never had a crack appear from the end of a cut I made into panel that I laminated back together.

DUB

 

I measured from the outside edge of the window trim (where the fiberglass of the upper deck starts) and it is 18 & 1/4 inches to the rear of the ducktail.

 

I want to thank Alan71 and Dub for this suggestion. I was planning on fiberglassing in place the 70-73 ACI rear clip and then sorting out the bumper bracket situation and that would have been a big mistake. Today I put the 70-73 ACI rear clip in place and test fitted the bumper brackets and it is clear I will need to be able to repeatedly remove and replace the 70-73 ACI rear clip in order to adapt the factory 69-73 bumper brackets work with the 79 rear frame crossmember which is different from the 68-73 rear frame crossmember. There just isn't room to figure this out with the ACI rear clip in place.

So, rather than as I had expected, I will be sorting out the rear bumper bracket situation before fiberglassing in the 70-73 ACI rear clip. If I had not fiberglassed the exhaust filler panel in place there may have been enough room to sort out the bumper brackets with the 70-73 ACI rear clip in place. So, in retrospect it was not a good idea to fiberglass the exhaust filler panel to the 70-73 ACI rear clip.

 

I think you're good on that,
I was going to suggest its time to take that next step and start glassing in,

But i am wrong, and its on to bumper bracket fabrication,

Sorry i didnt help any, but i also didnt post just to trash someone trying to help....

 

No problem Bats, I know you're just suggesting what you think is best.

 

Same here.....my '68 frame was simple without a collapsible crash ar, so I had no problem replacing the rear crossmember as an afterthought.

I can now see how modifying a crashbar would be a real pain with the clip attached............

Too bad you couldn't make the crash bar a "bolt-on" assembly once you finished modifying it.

 

Yes, I would have really liked to have more protection than a factory 69 setup but that appears way to difficult to work out.

 

There are numerous thoughts on the drilling of a small round hole at the end of a slit. It has to do with stress transmission, crack propagation and interlaminate shear.

Since fiberglass is a thermoset composite, there are different coefficient's of expansion between the glass and resin. Remembering that the glass provides the strength and the resin provides the stiffness and protection of the glass fiber. Also what must be taken into account is the structure of the glass; unidirectional, bidirectional, weave pattern, fold pattern or roving - milled or in-milled and finally if chopped mat w/wo roving backing.

By causing a round end to a slit the stress is better controlled.

I do agree that most times a repair on a car / boat will do ok due to the mass (thickness) of the fiberglass vs the stress induced.

But on a pounding race boat or a pressure vessel the result on a more highly loaded fiberglass panel will ultimately be different. (stress per square inch)

This may show up on a car that is lightly bumped in a parking lot by another vehicle.

We did tests in the lab with both thermal cycling and aging + flex and vibration testing using ultrasound and stress testing instruments and found the holes actually helped in most applications.

just some thoughts..

 

I can't help on this, since I have never done this but from what I have ben reading and seeing your doing a great job. Keep up the great work looks like your almost there.

 

This is a tool designed to mirror body work on both sides of a vehicle. It contours to curves in the body and you move it from one side of the car to the other and compare progress on the body work, things end up looking the same on both sides of the car. Great for repair of damage on one side of the car to compare against the undamaged side or custom work. Quite frankly pro results cannot be achieved without some way of doing this kind of measurement for comparison. I bought this from eastwood years ago. This car was hit in this corner resulting in the replacement of the tail light panel and repairs that extended into the top deck surface. It was a butcher job that all had to be cut out and redone. I could not have done a good job aligning things without this tool. For one thing it turned out the deck surface on this side of the car was a full 1/4" lower than it should have been as compared to the undamaged side.

On the bumper support issue. On my 1970 shown here, it's obvious to me that the bumpers do more than look shiny and offer little in the way of body protection. The bracketry supports the rear of the body structure. I don't know how the body is supported on soft bumper cars but on these early cars there would be a big overhang of unsupported structure that I would have no doubt would result in stress cracks if it were to be driven without solid bumper bracket support. I would not do any final glass work until the bumpers are 100% fitted to the rear clip. Successful restoration and custom work is achieved by things coming together all at once. Not finishing one thing and then hoping other related parts fit out of shear luck. You'll probably end up cutting things apart again or a butched job because you gave up on the idea of doing it right.

 

I've been looking at contour gauges hoping to find one 20-30 inches long with six inches of depth but couldn't find any near that long or with that much depth. most are 6-12 inches with 3 inches of depth.

 

The bumper brackets generally allow for adjustment from front to back and up and down. Do the holes in the rear frame crossmember allow for adjustment from side to side as shown by the orange arrow in the picture below?

 

Hi P,
Yes… some!!!!
The nut is in a cage that allows some movement. The nut isn't welded to the frame.
Regards,
Alan