Can you repair a cracked tail light lens cover?

[joep]

I noticed one of my tail lights on the Cayenne is taking on water after a rain or car wash. A crack has formed in the red plastic across the top length of the light but just enough to make a slight gap. It is not the seal, its the a crack on the lens itself. You have you almost feel it first to find the crack the plastic. It was easy enough to remove it and air dry it over night, and no apparent risk to the bulbs, body, or other electronics since the water is merely a little condensation gathered inside the plastic fixture. I once saw a the same thing on a CTT at a dealer's lot which had a small fish bowl effect going.

Short of replacing the tail light cover, can this plastic crack be fixed?

[BlackTalon]

Ken, I fixed a rock hole in a headlight cover on my Volvo with clear bra material -- it's work very well, and is not readily visible. And it lets all the light through.

[Vicegrip]

Crazy glue can be leaked into a crack that is held slightly open. The 3M film trick works well if the crack is not near an edge.

[joep]

This is on the main face of the lens, and about 1/2" below the top edge. I wonder if crazy glue is waterproof these days?

[smdubovsky]

super glue will fog many plastics over time. If it happens on the inside, you are SOL. If you can figure out what sort of plastic the light is made of, you can use glue to solvent weld it. Go to a hobby store and look for plastic glues. There are at least 2 major types (ABS, non ABS?? - anyway, cant remember.) They are water thin and clear. Buy one of each. Put a small 'wet' dot on the crack (or some other inconspicuous place) to test and let it sit for a minute. Then carefully wipe/blot it up and see if it made the plastic 'gooey' underneath. If yes, thats the kind you want. Its physically dissolving the plastic and when the solvent flashes off, the two sides will have 'melted' together. Good as new. It will make the outer surface gooey too so only put it on the crack (else there will be a frosted line where you brushed it on.) Since its thin like water, you can just blot on a little every inch or so and it will wick in.

There are few plastics that aren't solvent weldable. Nylon is one for example. But it doesn't come in clear;) Most acrylics, abs, etc will weld beautifully however.

[Dr K]

Stephen,
Will this work where there is some stress, such as a crack (going to the edge) across the screw hole in the lens?

[Vicegrip]

Works great if you have the solvent and a good applicator which looks like a little plastic bottle with a hypo needle in the cap. A properly set up solvent weld is almost as strong as the base material. Give the joint a day so the solvent can all migrate out of the base material. Just look at the standard format bong of the 1970's they never cracked at the base or stem seam they cracked through the stem or around the bowl threads.
Moisture will fog the solvent if it is present in any good amount during the application. If you use too much and a puddle of the solvent forms it can become so cold it will draw moisture out of the air and fog up. The solvent can make some hydrophilic plastics such as polycarbonate bubbly looking in the seam. If you have a drip run across the plastic don't try and wipe it up or blow on it. Ether action will just make it worse. Ether method will seal a light lense.

[Tedzilla]

"Just look at the standard format bong of the 1970's they never cracked at the base or stem seam they cracked through the stem or around the bowl threads.

^Some things never change.;)"

I couldn't say it better...

[good hands]

I've replaced 3 over the years. Common problem in cayennes. Bought replacements on eBay for about 200 a pop. 10 minutes to put new one on.

[Dr K]

I've replaced 3 over the years.

I swear I thought you were talking about bongs! :D

[Mr.Rodgers]

What about just putting a clear coat over it?

[joep]

What I wound up doing is getting a tube of clear silicone (not acrylic) windshield filler. I applied a small bead of that to make a fillet across the crack, and so far no rain to test it, but it looks good enough.