Antenna won't come out

A couple of weeks ago it was wash time for our Prius. A while back I had replaced the original antenna, where most of the rubber had flaked off, with one which was intact. The old one was very flexible and the new one not so much. So I took the new (stiff) one off and put the old (flexible) one back on. It went through the automated car wash with no problem. (Other than my having forgotten that to get into Neutral the lever must be held there for a few seconds.) Today I went to put the good antenna back on. No go. It spins easily, making a soft "thunking" noise as it turns, but it does not thread out. I tried pulling on it as it turned but that didn't help. My best guess is that the nut in the mount is now loose for some reason and is turning. Maybe the wash broke it, or equally likely, the brutal heat it has been exposed to for over a week did it. Unfortunately the old one isn't quite in there now, so some stations are not coming in well. Or maybe the wire inside the mount which connects to that nut is twisted up badly. Attached is a picture of what it looks like. Remember, all the rubber that is normally on the base has broken off. I don't see any cracks in the rubber, but there could be a small one right near the nut. Probably I need to replace the mount on the roof to solve this. Found a thread from 2009 but the link to instructions was dead.

Suggestions? In particular, is there a replacement antenna mount which doesn't need the antenna to come off at the wash but still works OK with the stock radio?

 

This is the post mortem.

My son and I pulled an antenna and base from a 2005 at the local "pick your part". Removing the old broken one and putting in the "new" one was uneventful, other than that 2 of the 3 clips holding the liner in back broke when they came out. Such are the joys of old plastic. The one from the 2005 worked. That antenna too was devoid of most of its rubber, so it was screwed out, and the replacement antenna which was purchased recently was screwed in. Of the 3 antennas (2007 original, 2005 from junk yard, replacement) the replacement one already has the most corrosion on the threads.

So, what went wrong? Let's start with the disassembled stuck unit from the 2007. From left to right, are: gasket that goes on the base of the mount, mount (viewed from underneath), 3 mount screws, circuit board that lives in the mount, odd nut/adapter thingy that holds the mount from the inside, (around the cable) O ring which seals part of the mount.



This is a little dark because for some reason or other the camera would not focus on the right spot if there was more light. Notice that there is some white stuff around the brass insert in the base of the mount where the antenna screws in. That is, a deposit inside the mount. A similar sort of deposit is visible just to the right of the circuit board on the metal base of the mount. That point is directly under the brass insert. So I think water of some sort was dripping in from the mount. But it probably wasn't going through the inside of the brass insert, as that is a solid blob of solder. The black insulation wire in the upper right corner of the circuit board originally went into the solder blob in the brass insert. It isn't obvious in the picture, but the wire is twisted around itself. Apparently once the insert became loose enough in the rubber part, that is the visible cone shaped part, of the antenna mount it would turn with the antenna. With the antenna mount off the car I tried various things to see if I could get the antenna out with the insert still in the mount: squeezing the rubber with big pliers, grabbing the insert on one side with long needle nose pliers with the other end on the outside of the rubber, and pulling on the antenna in one direction while pulling on the base in the other (with a helper, as this is a 3 hand operation). In each case the insert would rotate in the rubber, making its thunking noise as it jumped from one position to the next.

Here is the base of the antenna with the insert still attached. To get it out the rubber base "cone" was cut down to the insert with a hack saw.


The knurled surface of the insert is visible. That, set into the rubber, was all that keeps this insert from spinning in the rubber. This is the exact same dumb design decision which results in broken screw mounts in laptops, albeit there on a smaller scale. That is, "knurled insert set into soft rubber/plastic" is not a strong connection, so if the thing screwed into it ever sticks, that connection will break before the sticking issue is resolved.

Finally, here is the base of the antenna and the brass insert after they were unscrewed.



It took quite a bit of force to unscrew these, but once it broke free no force at all to remove it the rest of the way. There is very little corrosion on the threads on either piece. However, there is a light white coating at the two flat surfaces (top of the insert, bottom of the antenna above the threads). I think what happened is that at the car wash some water/soap got into this flat to flat interface. I didn't remove this "temporary" antenna right away, and over the next several days, sitting in the hot sun, that material baked into something very hard, effectively gluing the two pieces together. When I tried to remove it that bond was stronger than the one holding the insert in place, so it spun in the base's rubber, eventually twisting, and then breaking, the black insulated wire to the circuit board as it went around and around.

To avoid this, the rubber boot on the antenna needs to be intact, which is the case on the replacement antenna in there now. As an extra precaution, I put a drop of motor oil on the threads and that mating surface, wicked off the excess with a paper towel, before screwing it in (hand tight only). The oil does not interfere with radio reception. Some sort of grease would probably be better though, as that thin oil will probably evaporate eventually.