Bringing this back from the dead with some answers. Today I planned to do the quad sealed beam swap on my 1999 Suburban, but of course all the adjusters on the used units I got were seized up. Came upon this thread, and didn't really find any answers. Also couldn't find new units anywhere online. And I sure af wasn't gonna spend $300 x2 on complete new units just for a bunch of adjusters. So I took the plunge and opened one up to figure out what the deal is. I used a Dremel to cut around the outside of the cylindrical housing for the driven screw (the one that hooks into the headlight bucket) and popped it open. Here's a breakdown of how it works inside:
Very first thing is a brass washer:
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Under the washer is a brass gear:
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The brass gear is driven by another one that's attached to the top screw, the one we turn to do the adjusting. Removing the driven brass gear shows a plastic (nylon) threaded sleeve:
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And that's the cause of ALL the problems. That threaded sleeve is seized onto the driven screw. There's zero lubrication from the factory. Before I opened up the housing, I had tried penetrating fluid to see if that could loosen things up, but that was before I realized I was dealing with nylon threads. Penetrating fluid makes things worse because it causes the nylon sleeve to swell and grab the screw even tighter. This sleeve grabs a LOT of thread, so it creates a death grip on the screw:
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Once I realized what the problem is, the solution was simple. I grabbed the driven screw by its head in my vice:
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Then I used a heat gun to warm up the plastic sleeve, while trying to twist it with pliers. There's very convenient flat spots on the shaft of the sleeve, so there's no risk of damaging the gear interface:
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And sure enough, after a couple minutes, the sleeve freed up and I was able to twist it all the way off. I cleaned off the threads on the driven screw using a metal wire brush on a drill. All the corrosion I found on the threads was from brass shavings. So the brass gears create shavings as the adjusters are turned, those shavings end up on the threads of the driven screw, and they find their way between the metal threads and the nylon sleeve, which causes everything to seize up.
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I sprayed the driven screw down with PTFE lube. This is a dry lube with a solvent that evaporates quickly, so it doesn't swell up the nylon. WD40 sells it in a spray can that's very convenient. I also sprayed some PTFE lube inside the nylon sleeve. Then I reassembled everything. I put the cap back on the cylinder housing and glued it into place using Gorilla gel super glue around the outside edge. It all turned super smoothly with zero binding.
Now that I understood what the problem was, I used a different tactic for the next adjuster. I put it in the vice holding the driven screw head again, then I used a soldering iron to apply heat to the tip of the driven screw:
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With a T15 Torx screwdriver, I gently twisted the adjuster back and forth while heating the driven screw. After a couple minutes, the sleeve inside freed up. I continued to apply heat while working the driven screw out of the housing until it was relatively easy to turn, then I removed the soldering iron and finished removing the screw so the nylon sleeve could cool and form itself properly to the threads. Once the screw was out, I cleaned it up with my wire brush again, sprayed PTFE lube all over it and inside the adjuster, and put the screw back in. This should give an idea of how successful I was:
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So there we go, a solution to seized adjusters on quad sealed headlights. And anyone can do it with a simple soldering iron and some PTFE lube. no need to open up the adjusters at all.