lastsnare New Reader
11/21/12 11:09 a.m.

(I did some searching, but didn't see exactly what I was looking for, so here goes....)

I have a few extra sets of headlights for my 2004 Impreza (a small collection by now).

The problem is that many of them (bought used cheaply or expensively on eBay) have missing mounting tabs (not just cracked and present, but missing completely).

Situation 1: cut off one of the remaining tabs (still attached to one of the headlights) and stick onto another one that still has one tab, so that I have a few headlights with both tabs. This option could work, but a popular structural (strong) adhesive system seems to be a lot more expensive than I was hoping for. It looks like I would need Lord Fusor 152 or 153, plus the Surface Modifier (adhesion promoter ? or plastic primer ?) 602EZ, as well as the dispensing caulking-type gun (that has two plungers). In the end it looks like I will be dropping somewhere between $60-100. Hopefully there is a cheaper option.

Situation 2: For the headlights that are missing tabs, I would like to somehow fashion new tabs if possible. The stamp on them indicates PP (polypropylene) of some type. It looks like I could purchase a 12" x 12" piece of 1/4" PP from a distributor or Amazon for between $7-$15, cut and drill out some tabs, and somehow secure them to the housing (probably would need the expensive glue again, or buy a plastic welder, or hack at it with my little soldering iron and hope it doesn't turn into mush).

Any suggestions on a cheaper alternative to the Lord Fusor stuff ? It seems like it is the best adhesive for the job, but it's a lot more than I had hoped to spend. I saw mention of using a particular type of Loctite (it was mentioned on a Corvette forum as I was Googling), but it supposedly got mixed reviews, some people said it wasn't strong enough. Any GRM solutions to missing headlight tabs ? my past experience with epoxy is that it never seems to stick to the plastic well, even if you added fiberglass or maybe a mesh, it seems like the joint wouldn't be strong enough to not snap off or crack as soon as I tried to bolt it onto the car.

Open to fantastic and creative ideas :D Thanks !! Nate

andrave HalfDork
11/21/12 11:30 a.m.

I repaired motorcycle headlights that had the tabs broken off by using fiberglass cloth. If you use emory cloth to rough the smooth surface of the headlight, then wrap the mounting surface where the headlight bolts to the car with plastic or tape, you can soak some fiberglass cloth or mat in resin, apply it to the headlight, and then put the headlight in position so the mat will cure on the bracket, assuing the correct shape. You can also wrap the mat or cloth around a piece of plummers strap for a more secure bracket that will hold the bolt hole you will drill in after it cures better.

lastsnare New Reader
11/21/12 12:20 p.m.

thanks for the tips andrave ! I do have some matte and resin at home, so I will give this a shot on one of the headlights and see how it goes.

Hal Dork
11/21/12 1:54 p.m.

I have fixed a number of headlights and similar items by cutting tabs off other broken ones and welding them with my soldering gun. But I do have a Weller D650 300 watt gun.

If it does need to have some filler I just cut some small pieces from the donor item. If you cut long thin strips you can use them just like plastic welding rod.

I have also seen a person use an industrial heat gun that he made a custom concentrator tip for to puit all the heat in a small area.

lastsnare New Reader
11/21/12 2:10 p.m.

That's a good idea, thanks Hal. I found a video on Youtube where someone used a heat gun to soften some filler plastic too, that sounds like it might be good also. And he used a metal mesh square that he melted into the tab material, which seemed like it might not be a bad idea also.

Kenny_McCormic HalfDork
11/21/12 2:56 p.m.

Hazard Fraught plastic welder?

lastsnare New Reader
11/21/12 3:05 p.m.

that's an idea too. I would just have to see if my little HF air compressor is sufficient for it to operate

motomoron Dork
11/21/12 9:11 p.m.

the issue is in matching the loads to the material properties, and designing a repair that capitalizes on that.

By which I mean: If the housing is polypropylene - nothing rigid sticks to it - so if the idea is to make a relatively thin tab and bond that to the housing by it's 1/4" x 1" base then apply load, it's not going to last long.

Adhesives like silicones, urethanes, modified silanes and whatever Goop and Shoe Goo are are strong enough in shear and sort of OK in peel so they potentially could adhere an L-shaped bracket with a couple square inches of area to glue to.

I'd recommend another approach: Make a new bracket out of 16 gauge steel with a generous, broad base. Drill the 4 corners of the base 1/8", prime, paint, and adhere with a generous amount of GE silicone. After it's cured, drill the housing under the pilot holes in the bracket put a blob of silicone on each, and pop rivet.

Won't leak, will last.

lastsnare New Reader
11/22/12 9:31 a.m.

Strength is the biggest thing I had worried about. Years of building plastic models with superglue ( <--- is tricky and messy at best ) and past attempts to attempt gluing plastic have left me with little confidence in typical glues. The steel sounds like a good idea too. I don't have much in the way of tools to work with metal ( like cutting it or bending it if it requires more than a bench vise and a hammer or pliers ), but I'll consider this as an option as well. :)