Headlight switch mounting

[Mesozoic]

My '00 Mounty's dash panel is taking a beating. The headlight switch is loosely floating around in the cavity it belongs in, pieces of broken plastic prevent it from being firmly affixed to the dash bezel it was originally mounted in. What is the best way to fix this stuff? I'd love to fabricate some aluminum sheetmetal to solve the problem, but the curves in the dash make it a bit difficult. I just need to get that headlight switch mounted firmly so that it doesn't pop off again the next time I hit the trails.

 

[koda2000]

You could probably reattach the switch to the instrument surround using JB Weld. I fixed a completely broken fog light bracket using JB Weld. I dries as hard as steel. Only thing is you have to give it enough time to setup (min 12 hours).

Or you could just get a used bezel off eBay, or better yet the salvage yard (much cheaper). Is it the panel or the switch that's broken? The switch is held on with 2 screws.

 

[97Sandbox]

I recently came up with what I think is a pretty decent solution for this "loose headlight switch" issue.

As many who have braved the journey to the instrument cluster know, the root of loose switches is usually cracked screw bosses. The panel around the instrument cluster is polycarbonate, which is great at absorbing impact, but tends to be brittle so it can chip easily if it's not very thick. Due to a variety of causes, these screw bosses can crack and leave you with loose headlight and/or dimmer switches which are annoying if not disruptive.

After a couple iterations of super glue repairs didn't hold up over time, I recently attacked my panel with more in-depth plan.

1. Make new, thicker screw bosses from Nylon. I used 1/2" spacers from the hardware store. Instead of thread-cutting screws, I epoxied in brass thread inserts to allow the use of machine screws for holding in the switches.

2. Remove and replace cracked screw bosses. I used a Dremel to do this -- be careful how far you grind and wear glasses and a dust mask (the polycarbonate dust is nasty). I suggest leaving the "guide pin" bosses in-place to help with realigning the switches and use as added support for the new screw bosses.

3. Attach new Nylon screw bosses. Epoxy works fairly well to meld everything together, but I had one boss break free upon initial reassembly. To reattach, I had success with Loctite #406, which is basically a super glue specially formulated for these plastics.

4. Adjust screw bosses and/or switches to fine tune positioning. Nothing fancy here; if your bosses aren't perfect (mine sure weren't) you'll have to grind away material to make clearance for the switch housing and get the mounting tabs to lay flat. I just used a Dremel and a lot of guess and check.

5. Reassemble. Now you can install your switches with cap head machine screws! I didn't apply any kind of thread locker so I'll have to see if the screws loosen up from vibration over time.

And from the front it looks totally stock!

 

[97Sandbox]

Follow up tip: If you're lucky enough not to have cracked screw bosses, or if you're working on other assemblies that use screws into plastic, keep this in mind:
Since plastic is relatively soft, screws stay put primarily from friction on their threads, not by stretching the shank and developing a clamp load like traditional fasteners. To develop that friction, the screw's threads actually cut into the interfering plastic. This works well, but only once as you will weaken the plastic by cutting more threads with each reassembly (imagine cross-threading a bolt each time you reinstall it).

So how do you reinstall thread cutting screws? Find the threads originally cut and follow them. This can be done by carefully rotating the screw COUNTERCLOCKWISE up to one rotation and at some point you will feel the first thread "step" into the previously cut groove. This will orient the thread where it needs to be and you can then tighten it normally. I suggest only tightening screws until they're snug -- remember, the plastic squeezing the threads is what keeps the screws in, you're not tightening to induce a clamping load like you would for a bolt.

 

[dfd442]

Follow up tip: If you're lucky enough not to have cracked screw bosses, or if you're working on other assemblies that use screws into plastic, keep this in mind:
Since plastic is relatively soft, screws stay put primarily from friction on their threads, not by stretching the shank and developing a clamp load like traditional fasteners. To develop that friction, the screw's threads actually cut into the interfering plastic. This works well, but only once as you will weaken the plastic by cutting more threads with each reassembly (imagine cross-threading a bolt each time you reinstall it).

So how do you reinstall thread cutting screws? Find the threads originally cut and follow them. This can be done by carefully rotating the screw COUNTERCLOCKWISE up to one rotation and at some point you will feel the first thread "step" into the previously cut groove. This will orient the thread where it needs to be and you can then tighten it normally. I suggest only tightening screws until they're snug -- remember, the plastic squeezing the threads is what keeps the screws in, you're not tightening to induce a clamping load like you would for a bolt.

Thanks for taking the time to share this. Can't believe I am the first comment as this problem is pretty endemic. Could you share details on what kind of brass inserts you used? Did you match the thread # to the factory screws? (not sure what that would be).

Thanks again!

 

[97Sandbox]

Thanks for taking the time to share this. Can't believe I am the first comment as this problem is pretty endemic. Could you share details on what kind of brass inserts you used? Did you match the thread # to the factory screws? (not sure what that would be).

Thanks again!

I just used some thread inserts from the hardware store which had an outer diameter close to the inner diameter of the Nylon spacers (roughly a quarter inch iirc).

I think the screws that match those tiny inserts are #6 machine screws -- you can't reuse the original screws because those are thread-cutting screws designed to go into plastic and have a much steeper pitch.

All of the spacers, thread inserts, and screws were available at my local Home Depot. I'd guess the total was around $10.

By the way, I've had no issues with this repair holding up over the past several months.