I was calling around here the other day getting quotes on a paint job and one guy said that vettes are notorious for having stress cracks in the fiber-glass that you would have to fill and all of that. Does this guy know what he is talking about? Has anyone every heard of this before in regard to a C4?

 

I think the most notorious place for a stress crack to occur is the corners of the rear hatch, just aft of the doors.

 

I know that the c3's are really bad about stress cracking. The design of the body panels of the c4's (I think) was done with the thought to try and eliminate them as much as possible. I can only speak for myself...I have not seen that many c4's with stress cracks! One of the possitive things about c4's!

The main thing ( I have heard and seen) about painting any fiberglass car is to use the correct sealer to not let the air or moisture in/out of the pours. Make sure the person you choose to paint your car is experienced in fiberglass. You might want to do some searches on this subject, I am sure there are many here!

Good Luck!

 

I gottem. Rear deck and hood. 56K car, vert.

 

After 186k miles I found one on my hood. Allow me to speculate a stress crack may be an indicator of rough handling.

 

My targa has cracks from previous owners misshandling.

 

The C1-2-3 had problems with cracking, especially around the headlamps, and through the gell coat. The SMC glass took care of most of those problems, though they (C4's) still crack right at the corner of the hatch as mentioned. Targa tops are mostly due to the plastic deteriorating, I haven't run into the problem with fiberglass targas.

 

56k miles. 1987 Vert.

No stress cracks, but the car was repainted in 04 or 05(forget which year). The older ones seems to crack more. My dad's 63SW started to crack through an 8 year old repaint(paint in 80, bought in 81, sold in 88).

 

Stress cracks were more common before the C4's because the panels were bonded together. C4 panels are bolt ons and separated by trim. Huge saving for GM and C4 owners. My 72 looked like a one piece body and in the right light you could see the seams. Sounds like the painter wants some of the Vette tax. Every panel can be painted and matched without doing the whole car.

 

Stress cracks = fiberglass.
Its actually the hardest part of a fiberglass repair. Collison damage is easy to see but stress caracks are harder to see, but once the car is painted they show up real well.

What they mean is that a fiberglass panel has flexed beyond its designed parameters. Basically the gel coat is fractured.

Corvettes are made up-side down, boats are the same way.
The gel-coat is sprayed into a mold and then the fiberglass is sprayed over that.

Stress cracks appear over the fiberglass under layment.

It is the gel coat cracking, the gel coat is fiberglass without the glass fiber to make it stronger.

Its pure resin.

 

The back half of a C4 is still bonded together and bonded to the body under the roof pillars and etc with adhesive.The bumpers and front fenders,doors,are bolt on.

The C5 has bolt on 1/4 panels and etc.

Btw,to whoever wanted to know,The C4 doesnt usually have the stress cracks the older fiberglass Vettes had,the body is molded differently.

You can still get cracks in thin areas,and they can be grinded down and refilled with a specific smc filler.

Alot of stress cracks you see on C4's is nothing more than paint cracks in the areas.Once sanded down,the panel is usually intact.The body man needs to sand the area down to see if its paint or actual body cracks,but with the C4 shell,its a easy fix.

Its not to be confused with older fiberglass cars with stress cracks coming through from the inside out.SMC body panels on the C4 were created differently than the older fiberglass cars.

If I remember correctly,the body panels had a filler/resin poured together,then pressed together at high temps to create a body panel.It wasnt a sprayed release mold with hand laid or glass mats or brushed on resins.

 

I had my car repainted in 2001. The car is garaged 99.99% of the time, so the paint still looks new.....except for the 3 stress cracks that showed up next to each headlight assembly sometime around 2005. It happens.

 

I'll agree with whoever says that cracks which appear in a C4 paint job are Usually (not always, but most of the time) NOT the SMC itself but only the Paint. Too thick (too many layers..), incorrect primer and/or sealer for the SMC panels, etc. The paint will be cracked, and when you sand down thru it you find that there is Nothing going on with the panel below. This panel material has a Lot of flexibility and will cause cracking even in "good" Urethane paints. Visible cracks in the Hood either over the motor or around the headlights/hinge mounts are probably Only in the paint.

That said - I Do have a "crack" in mine. It actually appears to be where Someone tried a half-a$$ed "repair", for whatever reason - at the corner of the drivers side hatch opening, right over the drivers left shoulder. I know that this is the location a lot of folks think the quarter will "stress crack" - but that does not appear to be what started this mess. It's also not what the problem is Now. That area Is, in fact, stressed/flexed by the twisting of the frame/structure which explains why it's so hard to Fix...

Whatever is was, it's a pain to make a permanent repair on - it had been been gouged out so that there is a pretty good (deep) crevice to fill, and finding an epoxy that will Stay stuck to it has been tough. I'm in the 3rd attempt right now - using one of the Repair Epoxy's with chopped up 'glass filler for bulk. It's been under paint now since about June - so far so good. The cold temps this winter will be the Real test...

 

And I have a 1" one at the corner of the hatch, just behind the drivers door. Passenger side has yet to crack. I'm sure it's just the rather thick layer of primer/paint on the car.

 

Paint cracks..............I like it~!

How many Corvettes have you repaired?

Anyway I still like it.

 

The front and rear bumpers can easily show or begin to show stress cracks, especially if they come in contact with an object (a lightpost, car, shopping cart, etc.) while the car was in motion. If the bumper(s) were repainted by someone who is not too familiar with how a Corvette body and its paint are structured, and if the above bumper contact situation occurs after a repaint, the likelihood of stress cracks appearing is extremely high.

 

Bumpers are a different animal. You need to strip the problem areas.

 

Once the body work side of this is fixed, what do you guys do to keep it from happening again? Is there a chassis mod?

 

Yes, don't run super stiff shocks.

 

What was the ball park figure ? Here in Wisco for moderate body work and it done right with the same color, you're talking around $15K