Pandora's Box: Fiberglass/Metal Mating Issue

S

sjepps

Barry asked me to post the pictures I have for some additional input. He is, understandably, wary of even working on the truck before I cut the glass out to see what the metal is like.

The truck was my grandfather's and I've spent over 400,000 miles in the passenger seat. So as far as I'm concerned it is going to get fixed, one way or another, no matter how much money I have to throw at it.

The issue with the cracking is a systemic problem for all of these trucks. Cabriolet did a poor job of mating the fiberglass to the metal. My plan is to cut it out, treat the metal, drill out holes for sheet metal screws and then slowly build up the glass around the screws (or rivets) until we're back where we should be. All of the loose pieces you see in the photos below are the glass. The windshield isn't currently leaking (How I'm not sure).

Barry suggested I disassemble the truck and have the entire thing sandblasted professionally. Which is good advice.

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You may want to carefully remove sections of that cap so the rust can be treated (blasted) and epoxied as you say, but I don't understand the building of 'glass around screws part. the cap might best be bonded onto the repaired and epoxied metal by using the right kind of 2 part adhesive. Screws can be used to hold the part down while the glue cures, but then they should be removed for seam filling and smoothing. The adhesive I would use might be something like SEM 39337. There are some tricks that can be done along the way, and SPI epoxy has become an important part of the repair process at our shop, especially when dealing with the bonding of dissimilar materials.
 
I'm on the fence as to whether or not to use screws/rivets to hold the glass down. The cap is pretty thick so using screws/rivets should not show up in the final product. This process was suggested by a couple of tech's at different fiberglass companies (US Composites and West). I'm worried that the flex that's seen at this point on the truck won't like the screws keeping it tied down and will result in cracking down the line.

Some owners of these trucks say the reason for the cracking seen is due to the fact that Cabriolet did not use this process on this year model. Later on they started adding rivets and the roof didn't have as much trouble. I don't know enough about glass to know if that is a good argument or not, just passing it along.

Are you suggesting I create a mold for the cap and replace it as a single piece? I had been planning on cutting out a good chunk of the glass, feathering the surrounding area, and then alternating mat with cloth for increased strength vs. the chopped glass that is there currently.

Thanks for the reply crashtech.
 
No, not a mold. I thought you were going to section pieces of the cap out so the metal roof could be repaired, then re-bond the sections back in place. There is more than one way to do this, but my take has always been that if it is to be bonded and smoothed in, then no fasteners should remain, but if you want it to be attached with fasteners, leave them exposed in the final product. For instance, if we were asked to install a fiberglass cap like that, it would either be bonded on with no fasteners, or bolted on with wellnuts and stainless hardware. No in-between. Sometimes a flange needs to be built up on the backside of the part to give enough surface area for bonding or bolting. My guess is that the method of construction on your vehicle was outdated and probably involved grinding the factory finish off the metal prior to bonding , which is an old school method that can still work, as long as an approved epoxy-based adhesive is brushed over all the exposed metal prior to part installation. I bet that wasn't done.
 
I hadn't really considered that crashtech. Thanks for the response. No one is quite sure how they put these things together, they tend to vary, but considering what I've seen I would think you're right on the money with that last statement. The doors are a trouble area as well, just not as large of one. I'll post some pictures of that just for show later today.
 
the trucks were built by people who had no clue. cheap materials , lacquer primers and inexperienced bodymen and painters. your best bet is to start over and redo what they did. use a good bonding agent then evercoat 870 .
 
Unfortunately shine I think I'm going to have to redo everything they did :p
 
shine, sjepps is going to need some help learning how to do this the right way. I know you are one of the 'glass experts on the forum and was hoping you could help out in this thread. I think sectioning out portions of the cap to do the rust repairs might be the way to go, especially if there is a way to get to the backside to reglass the cutlines. What do you think?
 
i spent a lot of years dealing with the custom van industry and believe me nothing was ever done right. if i were hell bent to restore it i would blast around the edge first to see what was there. most likely they took a grinder to it then glued it down with bondo. worst case would be to cut the front half of the roof off and repair the rust damage then bond it back together. it's not going to be an easy fix. but i believe getting the paint and filler off would be first thing .
 
Do you think the roof damage extends past the front windshield area? I haven't seen any damage on the inside of the roof but that doesn't mean much.
 
On some of these things, they cut the roof out to gain headroom and add all the custom stuff like lights and stereos, etc. That might be a plus in your case because it allows backside access to the repairs. If not, it's not the end of the world.
 
The metal portion of the OEM roof extends to the backside of the captain's chairs up front which is also where the roof incline starts on the outside of the truck.
 
So that means you will probably be doing all the repairs on the front part from the outside only, which is OK, just a little harder in some parts. We are way ahead of ourselves here, how about getting it stripped and posting some detailed photos?
 
Will do. I just like to have things swimming around in the back of my head. I'm starting at the back of the truck since I can refresh what little fiberglass experience I have there. That way if I make any non-aesthetically pleasing mistakes I can hide them pretty easily. Problems with the truck bed are mostly stress cracks. I'll start a build thread so everything will be in one place.
 
I would go back a foot or so and cut the fiberglass off all around at the mating joint....then I would go get a used windshield section and total replace, rebond, refinish...I wouldn't mess with rust repair....replace....Dave
 
Two ways to do it IMO, the rust has to be removed for sure. You can use the proper adhesive for bonding the fiberglass to steel or just make sure you put down 2-3 coats of SPI epoxy primer before using traditional polyester resin and mat. Poly resin doesn't adhere well to bare steel.
 
I'm planning on using epoxy resign on the glass when I replace it. Little more flex to it so I'm hoping that will help. I think I'll cut into it and see how it looks and go from there. Not averse to replacing the whole thing as flynams has suggested.

I'm on the fence as to whether I should try to cut out a large section of the cap so that I can more easily replace it or just cut the glass back. My only worry with cutting an entire section out is getting the underside loose depending on how well it is bonded to the roof.

Cutting the glass back would take longer to replace but would give me a better stronger cap I think.
 
sjepps;28566 said:
I'm planning on using epoxy resign on the glass when I replace it. Little more flex to it so I'm hoping that will help. I think I'll cut into it and see how it looks and go from there. Not averse to replacing the whole thing as flynams has suggested.

I'm on the fence as to whether I should try to cut out a large section of the cap so that I can more easily replace it or just cut the glass back. My only worry with cutting an entire section out is getting the underside loose depending on how well it is bonded to the roof.

Cutting the glass back would take longer to replace but would give me a better stronger cap I think.
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Yes...remove the front foot or so....using epoxy to patch the fiberglass is wasted money...polyester resin on ground fiberglass has worked well for 60 years
 
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