cdsinfla

I removed the seats from my 73 convertible to add new seatbelts.
Under the drivers side I found a crack in what looks to be fiberglass.
The 1st pic is for reference.
The 2nd shows the crack

Should I be worried or is this no big deal? When I push on the floor it squeaks a little but the crack doesn't really open up more. What made me notice was a flashlight under the car & I could see the light. Overall there is a little rust but nothing that seemed too bad.

69FASTFUN

I would fix it.

doorgunner

That's a good place to learn how to make a sturdy repair.....the carpet will cover up your work when it's completed! You'll gain confidence toward the next repair.

Brandons72vette

Yeah I would fix it, it wasn't there when it left the factory, so why keep it around?

It could expand and open up on you in the worst time and place.

I saw a few issues regarding my '72's suspension and ignored them and assumed I was "good to go" only to have the car end up in a sad wreck. While this is far from causing a wreck, IMO, I am going over my '72 now and plan to repair anything that I thought was "fine". There is a fine line between "fine" and "safe". Fix the crack, it can't hurt anything more than if it wasn't.


Post pictures and notes of the repair. Goodluck!

AdamMeh

I would fix it for sure.

persuader

Fix it. The jury has spoken.

F22

Besides fixing the crack, I'd suggest stopping it as well. I learned this weird trick from a B-29 Gunners manual on how to stop a crack from spreading. This was to stop cracks in the plexiglass bubbles. You drill a small hole exactly where it stops.appearing. The circumference of the hole, spreads the stress out in a circle, instead of a single point and stops the crack, dead in it's track. I've done this for years and it works really well in many situations.

F22

To fix the track, you're going to need fiberglass resin, hardner, a paper plate and a plastic picnic knife. But first you've got to stop the crack as described above. Next, you need to grind out the crack with a dremel, so that it has a V shape along it's whole length. I'd say that it should be a 1/4" to 1/2" wide. Take some 150 grit and scuff the area on either side about a half inch out, so the resin will have some traction. Vacuum the area clean and then wipe it good with acetone. Next, you would the pour a few tablespoons of resin onto the paper plate and then put twenty drops or so of hardener. Mix well and use immediately! If it gets hard before you can get it on, mix a new batch and cut back on the hardener. Apply with the knife, the mix the entire length of the crack, filling it and spreading it to the outside. It will not look 'perfect', as you're spreading 'goop'. Be generous with the goop, because you can grind and sand it down later on, to make it look nice. If the crack reappears (doubtful), you would have to treat it as a big fiberglass repair and use fiberglass matting across the crack. But I think this will work, the resin gets hard as a rock and now that you've stopped the crack at both ends, it should be ok.

Postal123

I agree with grinding the v-groove in the 'crack' to ensure penetration of the resin, but for this area I see nothing wrong with adding a few layers of fiberglass across the repair area for added strength. Who knows...maybe the area was slightly thin/weak in the first place? Hence the crack? Not sure what the underside is like, or what your plans are for that area, but I'd consider that as well. My only consideration to the above mentioned is whether or not you want to hide the evidence. Just my $.02

F22

It wouldn't hurt!

cdsinfla

F22 & Postal123, thanks for the instructions. I was just beginning to Google how to repair this.
I don't care what it looks like as it will be hidden anyway. I plan to patch the crap outta this thing. More concerned with the safety aspect. You never know what's hiding under the carpet in a 40+ year old car.

F22

A few layers is all you'll need. It's gonna be messy too! Buy a gallon of Acetone for clean up and use rubber gloves. It's actually pretty easy. Mix resin and hardener, apply, lay diwn the layers, and use a cheap, disposable 1" bristle brush to apply the mix with. It will bunch up, move and you'll have to adjust with your fingers, tryinv to keep the goop where it's supoosed to be, but it can be rewardinv, when it's all done.

F22

Don't be surprisd at how long it takes to cure too. I've had it take up to two days to fully harden, because I didnt put enough hardener in the mix. And I've had it go rock hard in five minutes, because I added to much.

cdsinfla

Picked this up at Pep Boys.
Do I even need the cloth? Or just the resin/hardener?

Mike Ward

That crack is right next to where the seat belt mounting plate attaches. I'd make sure it's properly repaired and not just from a cosmetic aspect.

Postal123

Definitely use the cloth! It's simple. Rough up the area very thoroughly with course sandpaper. Cut the cloth strip to desired patch length. Mix your resin/hardener. Best to use a paint brush here. Paint the surface with mixed resin; lay the cloth strips down, apply more resin with the paint brush, repeat. Recommend about 2 layers at time and continue to dap the area with the brush you used for application until it begins to set up...this will ensure the cloth layers lay flat (try to eliminate bubbles). If this is a new thing, don't worry you'll get the hang of it quickly. FYI - thick resin puddles are not nearly as strong as combined resin/cloth. Use enough to ensure the cloth is fully wetted, but try to avoid much more. For max strength with the type of cloth you've got, try alternating the direction of the fiber strands (straight cut, then a 45 degree cut, straight cut...) hope that makes sense...it's a common aircraft construction tech. For your repair, you'll be fine either way...it's just a tip.

v/r,
Rob

Postal123

Agree with rubber gloves. Also, recommend a few disposable cups and cheap 1" or so paint brushes (the $.95 natural brush deals). Caution: the resin will eventually eat through plastic cups as the hardener begins to activate. Have fun!

F22

Texas70

I could be wrong, but I believe the 1973 C3 were made with SMC. If that is the case, the polyester based fiberglass is not what you want to use. Again, google search to confirm this.

Brandons72vette

This same technique is applied to general aviation as well. Lot of aircrafts use a variety of materials, and fiberglass is one of them. On our 1981 Cessna 172, there are numerous cracks in the fiberglass tips of the wings, vertical and horizontal stabilizers, the engine cowling, and the landing gear covers. I can vouch for this technique, and if it is safe enough for aviation….you know it is safe enough for cars. While the little cracks are not very appealing, they don't take away an airplanes air worthiness (generally) and the cost to repair and repaint the panels would be expensive.