Better Beaters - Building Cars and Daily Drivers

 Plastics. 

"Remember one word. Plastics."

It was the wave of the future recommended enthusiastically to Dustin Hoffman in "The Graduate."

I remember back when household items were touted for their construction of "high impact plastic!"

Back then we lived in a dent filled world. Items like waste baskets, buckets, small appliances, and especially garbage cans would get banged around and end up with numerous dents. That would make them look pretty beat up. I was reminded of this when I was emptying the waste baskets in my Wife's studio. They are wire mesh units that were purchased at IKEA. I've accidentally put a dent in the sides, then I pounded them out by hitting them on the inside to straighten them out. Plastic items resist being dented, until a really serious impact causes them to crack!

Plastic also has another benefit, especially for outdoor household items, it doesn't rust. One piece resin patio chairs have been popular for decades. They do have their advantages. Folding aluminum  chairs with steel hardware would have the hardware get rusty, sometimes leaving unsightly rusty streaks. The major problem with resin and other plastics is it's susceptibility to UV damage. Exposure to UV light weakens the plastic, but sometimes you are not aware of this until the item suddenly fails. Lots of people, myself included, have experienced a collapsing patio chair. 

Metal items can be repaired easily, dents can be straightened, cracks can be welded, or broken areas can be bridged with mending plates. Replacement parts can be cobbled together by the home repair person, restoring a broken item back to a usable state. Plastic is a different matter, sometimes it can be repaired through mechanical means like mending plates, and reinforcing brackets. Although the most common repair is by using adhesives. 

So plastic has it's place and it's usefulness.

But it's the bane of the old car guy.

At one time, the trim pieces on cars were made from steel, cast zinc, glass, stainless steel, and minimally... plastic. Now almost every panel inside is made from some combination of plastics.

Is there anything worse than 25 year old plastic?  How about 15, 10, or even 5 years old? 

It was bad even when the car was new, and parts broke during warranty related dealership servicing. They even broke frequently during the cars assembly process! But they had the option of grabbing a new OEM part out of a bin.

I was there in '77-'81, screwing together Chevy Monte Carlos in Fremont. I thought that there was an awful lot of plastic in the dashboards, door panels, even the header and tail lamp panels. It didn't look like it would last a long time, but I wasn't  thinking about them making it past the New Millennium. It just had to last long enough for me to finish my installation. Miraculously, the lifespan of these parts has exceeded my meager expectations. 

Realistically, a manufacturer has to build an item to last through the warranty period and to provide it's purchaser with a reasonable period of reliable use. I'm sure that automobile manufacturers didn't conceive that examples of their products would become collectors items and be kept in use for 25, 35, or even 55 plus years. 

But they have.

One of the most worrisome events is the initial disassembly of a section of an old car's interior to gain access for diagnosis or repair. Removing dash or door panels is fraught with the potential for damage.

It can be almost impossible to do this without causing even more damage. It's like doing CPR on a 90 year old person. The intent is to save their life, but how many ribs are likely to be broken in the process?

Sometimes you can find how to videos that can give you a good heads up on how to proceed. Other times you have already gone to the wrecking yard and disassembled parts of a donor car to get the parts you needed. But you may have broken some mounting tabs or pins in the process. But now at least you know how the panels were attached and fit together.

There are various types of plastic used in the construction of a car's interior and bodywork. 

Polypropylene is one of the most widely used materials in construction of a car's interior. It is also used for bumpers, carpet and other floor coverings. 

Polyvinyl chloride,  PVC, is commonly used in dash board and body parts.

Polycarbonate is highly impact resistant, and used in bumpers and headlight lenses.

Acrylonitrile Butadiene  Styrene, ABS, is used in steering wheel covers and dashboards. It is well suited to heavy duty applications like body parts.

Polyethylene is used in glass fiber reinforced car bodies as well as electrical insulation.

Nylon 6/6 can be fabricated through molding or extrusion techniques and is often used in weatherproof coatings.

I wish that I could tell you exactly where these plastics are used in your particular car. Just being able to properly pronounce the names of these types of plastics will lend you an air of authority! But I'm no chemist, my only interest and concern is how to repair broken items made from these materials. 

The important question is: Can I find a commonly available adhesive that can bond the broken part? 

How do you repair the damage, and reattach the part in a workmanlike manner?

How can you fix broken plastic pieces like mounting tabs or molded posts? 

Adhesives are a first attempt. Usually superglue or JB Weld. But the glue has to stick to the original plastic. This is the biggest issue because the somewhat flexible PVC plastics will often not bond with super glues. Sometimes good old plastic model cement will do the job. 

Epoxies like POR 15 are another route, but again will they stick? 

Silicon calks and sealers can sometimes work. Especially if there is a large area for adhesion.

Plastic welding works for some plastic panels.

A hot glue gun? 

It's easy to test the efficacy of the glue on the back of a panel, if after drying, it can't be easily scraped off, then it might be a good candidate. 

It also depends on the job that you are asking the glue to do. Is it holding something like a badge, lens or small panel in place, not much strength is called for. Or is it to repair a broken part like a cover panel or lens?.

Is it going to be used to fix a broken mounting bracket, locating pin, or other piece that completely snapped off during disassembly?

How much surface area is there for adhesion at the break?  A wide jagged shoulder or a narrow knife edge? 

Sometimes the fracture can be splinted with a supporting piece, using another layer of plastic, or what I've favored, something made from aluminum flashing. The flashing is easy to cut and shape. In many spots I used a combination of small screws or pop rivets and an epoxy glue. If there is enough room to accommodate the splint it works fine. 

The repair pictured above was one of my more ambitious splinting projects. The curved section is attached to part of the steel tube framework. Then the metal was bent to a ninety degree angle and screwed into the plastic leg. The front leg of my Wife's rolling cart was broken when it was dropped off a stair step. The part was cracked, but still attached by a section of intact plastic. My splint holds the leg in place as well as bracing it from moving back and forth. There was no way that glue applied to the edges would be strong enough to hold. Since the repair is underneath and out of view, aesthetics aren't a primary concern.

I formed this splint by hammering on a piece of aluminum sheet clamped in a vise, after it was roughly cut to size. Sometimes a simple mending plate can be used to bridge the broken area. 

If the broken part is part of a plastic door card you have to be careful that any screws or rivets aren't visible through the upholstery, or protrude through to the other side. 

I'm not a great fan of duct tape, but it is quite sticky and it can cover a large surface area for maximum adhesion. 

The biggest challenge is if the plastic part needs to have some strength, for example the door pull cup or strap, molded into the door panel. In my Rivieras case, the middle of the door panel is held on by three curved plastic prongs that hook into the doors steel panel. The door pull strap has screws that are attached to metal, but the middle of the panel can get floppy if the hooks break off of the door card. 

At one time, up to the 1950's and '60's, door panels were held on by a combination of hidden clips and visible external screws. Now visible exterior screws are avoided. Although it will be visible, and look like an amateur repair, sometimes a screw drilled through a panel into the metal underneath is the best option. It is certainly the easiest option! 

The end result of this discussion of plastics used in automotive construction boils down to one reality: I've got some broken parts that I need to fix.