How do I unscrew a screw that turns freely?

April 5, 2011 4:29 PM

What do you do with a screw that turns freely and won't unscrew? I'm trying to replace the brake light bulb on my Audi A4, but the screw that holds the brake light assembly in place turns and turns without unscrewing. I assume that the corresponding nut is loose, or that whatever it seats into is broken, but I'm stumped.
posted by bonecrusher to travel & transportation (13 answers total)

try a magnet to get it out?
posted by Max Power at 4:32 PM on April 5, 2011

Reach some kind of a hooked piece of metal behind the head, and pull out as you unscrew.
posted by StickyCarpet at 4:36 PM on April 5, 2011

gently pull (pair of pliers) while unscrewing?
You're in the trunk right? I think there's very little actually thread to get to the assembly and tends to pop right out
posted by oldefortran at 4:37 PM on April 5, 2011

It's likely threaded into plastic and the thread are stripped. Either pry it out gently as you turn it (with a flat screwdriver under the head) to try and force it to remake it's own thread, or you'll have to try and hold it while you drill the head off.

I'm assuming you can't get to the back of the thread to push it or other wise check there isn't a nut insert that is spinning? If you can get to the back of it, pushing it either out or against the side of the hole will create a kind of thread to get it to screw out, too.

It's not fun, and there's a chance you'll crack your headlight bracketry if you don't take care. Especially if you mean the screws that go from the outside of the car (ie facing backwards) straight through the light itself into the car. Because it's recessed, you may be in big trouble, there. Drilling that out won't be fun.
posted by Brockles at 4:45 PM on April 5, 2011

I assume here that the screw is in the trunk? It's possible that loosening it just detaches the assembly from the chassis, so that you can just carefully remove it without losing the screw.

Most light assemblies have plastic or metal pegs that hold them in place, so check if those are the only things holding the assembly in place. What year is your car?
posted by CancerMan at 4:48 PM on April 5, 2011

Are you sure you're doing it right? Granted I've no specific experience with the A4, but every Volkswagen product I've owned (and assisted with) has had tail lights with an easily-removable "tray" which holds all of the bulbs. Pinch the plastic tabs and it pops out, no tools necessary.
posted by bhayes82 at 4:48 PM on April 5, 2011

2004 A4 3.0 Cabrio.

Brake light housing is definitely held in place with a screw (the light housing on the other side came out fine). I'm going to go get my pliers and try to pull as I turn - it's really hard to get a grip on the screw head.
posted by bonecrusher at 4:54 PM on April 5, 2011

Apply a good hot glue to the screw and insert screwdriver in to hot glue while glue is still liquid. Hold till dry.

By good hot glue, I mean that will pry off in a neat way once dry. Experiment on other disposable plastic surfaces first.
posted by fief at 5:45 PM on April 5, 2011 [1 favorite]

Well, further experimentation shows that the rubber housing on the side of the brake light assembly can be removed, exposing the socket that the screw seats into. The plastic that holds the metal socket is cracked, allowing the socket to turn freely. I think a little penetrating oil, plus holding the socket in place with a pair of pliers will allow me to unscrew the screw.

Thanks for all the help everyone. I just can't pay someone to replace a brake light.
posted by bonecrusher at 6:41 PM on April 5, 2011

if you can get a flat screwdriver under the had of the screw and lever it up until you feel pressure then unscrew it. That has the effect of holding the nut against a bulkhead.
posted by the noob at 6:56 PM on April 5, 2011

If you can access the metal socket/plastic interface, put a drop of superglue on a toothpick or wire, and dab it to the interface to "freeze" the socket (we're talking about the oddly-shaped nut, essentially, right?).

Superglue likes a moist surface; heavy breath or a dab with a wet q-tip may suffice, if it doesn't "take" on its own (as is sometimes the problem). Or use airplane glue and 15 minutes of patience.
posted by IAmBroom at 7:00 PM on April 5, 2011

Jimmy a small screwdriver behind the head and pry just a little while unscrewing the normal way. Once you can get fingers on it, use them.
posted by notsnot at 7:08 PM on April 5, 2011

Um...are you sure you need to remove the entire housing to change the bulb? Generally, brake lights are accessible from inside the trunk, by pulling-back the trunk lining to expose the back of the lamp assembly. The carriers for the bulbs should simply twist-out from the assembly.
posted by Thorzdad at 5:14 AM on April 6, 2011