Plastic headlight re-sealing

[Pontisteve]

Ok, I've gotten the buffing out of plastic headlight assemblies down to a science, and have absolutely perfect results there. But only if water has not gotten into the headlight. Outside of cracks or damage, it appears water gets into these headlights thru bad sealing. Particularly older headlights, as they seem to use a black gasket-like material to seal the lens to the housing. Newer ones appear to be put together with a whitish-tan caulk.

Does anybody know what exactly this caulk is, and if the factory caulk can be released with a heat gun without having to melt the lens itself?

[rabmotorsports]

Well, I have never had real good luck with trying to re-seal plastic headlamps. But as an alternative I know the Mustang headlights are bad at getting water in them, and all I do is take them out and drill 2 small holes in the bottom to let the water drain out. Not real high tech, but it works.

[Pontisteve]

I've done that too, and it takes care of the water. But... in order to keep the inside from molding and turning yellow, the seal has to be intact or the weather gets in. I don't know what sealer the factory uses, but surely its out there. The big question is can you break apart the lens using heat without destroying it in the process. Even a yellowed lens with weather damage could be rebuffed and resealed if there was a way to get inside. Anybody?

[Restobutcher]

Pontisteve,
You pose a very interesting question, that is...how to disassemble a composite headlamp unit. Typically the lens is formed from polycarbonate, with the housing being formed from either polystyrene or PBT (I could spell out this abbreviation, but can't pronounce it!) Bonding these two somewhat dissimilar plastics proved to be a challenge in the manufacturing process due to the need for high bond strength, flexibility, quick cure and permanance (sorry Ponti). OEM's have opted to use a UV-curing acrylic adhesive for the task, specifically an adhesive in the urethane methyl acrylate family. It's applied robotically, then passed through a curing tunnel where UV lamps cure the adhesive almost instantly. Typically, adhesives in this family are either grey or black. Since the composite joints actually overlap, there is little opportunity to manually cut open the closure, and to my knowledge there is no solvent that will disolve the adhesive without destroying the adjoining composite. I wish that I had better news for you!

The Butcher

[Cloud59]

Headlights – I am almost certain that type of headlight may be a heat swaged assembly and not serviceable. I would obtain another one from a similar car out of a salvage yard even if it is in poor condition to experiment on. The polycarbonate lenses generally have good heat resistance so it may work. Try a hairdryer or heat gun on that one to see if it is damaged in any way. RTV would make a good sealer if disassembly is successful.

[Pontisteve]

Actually, my headlights are in great shape. No bad news here! But in my quest for perfection, I became interested in how to fix other peoples. There is a grayish tan seam sealer that is used to connect the lens to the housing. And you're right they sealer is recessed and you can't cut it out. Im sure there is probably some body shop quality sealer available that probably would put them back together again, but I was curious if anybody knew anything about taking them apart. I seriously doubt the factory ever meant for the newer lights to be serviced. I think the older generation may have a shot at coming apart safely though.

I'll throw in a pic of my 97 Mustang headlights for fun. I wetsanded them with 360 fully, then 600, and then buffed them out with plastic polish on a spiral sewn and then a loose buff. Gotta watch out for the spiral sewn one. It'll burn ya if you're not careful. The loose one is safe to go pretty crazy with. If I had it to do over again, I would consider a third wetsanding stage with perhaps 1000 grit to cut down on the time required to polish out the 600. I took these pics at night, but I can assure you the picture doesn't do it justice. They're perfect. I actually argued with a guy this weekend who wouldn't believe they weren't new.

[Dr. Scampy]

Steve,
Nice job on the headlamps!!! In fact, Eastwood sells a small kit for the DIY'er that will achieve comparable results in a shorter amount of time (for less $) & there is considerably LESS worry of damaging the lens w/ the buff wheel enclosed... The part # of this kit is 52267 & it sells for $15.99... it includes the following items:
1 - 3" buff wheel (#13039)
1 - 1/4" shank mandrel for buff wheel (#13064)
1 - tube of Autosol paste polish (#13170)

This kit is designed to be used w/ an electric drill in the 1800-2200RPM range & will yield similar results as your method but w/ less time involved. In extreme cases I too have wet-sanded first, starting w/ 600, then 1500 & finishing up w/ 2000. I then followed the wet-sanding steps w/ the above kit. This method has produced brilliant results that have GREATLY improved my night-time driving vision & saved a few "run-in's" w/ deer!!!

[Pontisteve]

I've heard of Autosol, but never tried it. The interesting thing I found over the years about headlights is that you have to sand thru the surface a little, because what appears to be happening is the surface microscopically cracks. Then the mold sets in the cracks and gives the yellow appearance. I've buffed em a million times with car products and rubbing compound etc. only to find that it doesn't do that good of a job, and it definitely comes back!

Also, as I live in FL, we have love bugs that etch quite deeply into the plastic and sanding through their pitting is the only way to achieve perfect results. One VERY interesting thing I found about plastic is that its more like working with aluminum than it is with paint. I was always afraid to get aggresive with them (i.e. 320 grit), but it turns out my fears were unfounded and I was working with fine 1000 grit type paper for nothing, only to have to work longer. The 600 grit is close enough to buff out with plastic polish, but if you use perhaps 800 or 1000 after that, you save some work in the polishing stage.

I've wanted to try the many kits available to see if they do a good job faster, but I figure if it takes sandpaper that rough to cut through the worst of it, then there is no way a liquid can make the cut. All I can say for the way Im doing it now is the results are absolutely perfect... after a mere several hours of hard work :-)

Total cost: 4" loose buff - $4, Plastic polish - $8, Sandpaper - $3 Total : $15

[Restobutcher]

Pontisteve,
Nice job on those headlamps! You've definitely got the technique down. Your observation that the discoloration will return over time is accurate. Interestingly, the polycarbonate lamps are attacked by three things over time...that is heat, UV light and ground level ozone. You've got plenty of that in good ole sunny Fla. (the first two from the sun and the ozone from vehicle emissions). Autosol is awesome stuff and does contain protectants, however their durability in that application is limited. I have had luck wiping on a light coat of acrylic floor wax over the lens after performing the cleaning. This is not a tried and true method, nor endorsed for that matter, but it works for me.

The Butcher

[Dr. Scampy]

Steve,
Obviously your method & mine are somewhat different yet our results seem to be the same... I guess MY approach was more geared towards time savings & since the products in the #52267 kit are more than enough to do several pairs, I shoot for the quicker method. I just did my brother in-law's headlamps on a '92 Dodge minivan (w/ out using the drill) w/ the 600, 1500 & 2000 then followed it up w/ the Autosol by hand & they looked as clear as yours... BUT, I did the pair in 10-15 minutes. I would rather do them 2x / year for 10-15 minutes each time than spend a few HOURS on them & probably NOT have them last for much longer than a year or so.

I did have another question for you... are you mounting that 4" wheel on a bench-grinder or motor of some sort? I can't remember what you said previously... IF so, then I am assuming that you are removing the headlamps from the car to buff them... correct? Please respond