Sorry for starting a new thread. I know there are a lot same topics out there but I didn't find anything similar.
Long story short, I fixed the power antenna last weekend by following the instructions on the forum. Opened up the antenna motor and took out the broken piece of white plastic. Put in the new antenna. After a few adjustments, the new antenna goes up and down like new! This morning when I started the car with radio, the antenna goes up normal but the motor wouldn't stop pushing even the antenna is already pushed all the way up. I hear the motor teeth was grinding the white plastic tail of the antenna for about 10 more seconds before it stops. Turned off the radio and the antenna retracted fine without extra grinding. It seems to me that somehow the motor does not know when the antenna is already pushed all the way up. Anyone had same issue? How do I fix it?

When mine died I scrapped it and went with the tacowhip instead, no moving parts = trouble free operation. I don't have an answer for you, but I imagine replacing the antenae will quickly become expensive if it keeps chewing the teeth off the new ones.

When I replaced mine, the motor did the same thing and ended up breaking the new antenna right after I had put it in! I just said screw it and left it pushed down. The Taco Whip Mod is the only other way to go, IMO. The replacement is just going to break eventually.

Yeah... I felt the same way too. But my antenna is just one day old!
I think the issue is that the antenna motor should stop pushing/pulling when it detected a traction (antenna all the way and all the way down). Mine is just too much power. Is there a way to adjust the motor's sensitivity?

Not easily. When I did mine I took everything apart and cleaned it all really well and greased it.

1) I'd stop using it right now before it ruins the new one (if it hasn't already).

2) Take it back out and take it apart clean and lube.

When you put back in, make sure you feed it with the teeth going the right way. For the 2000+ I believe it's toward the front the vehicle, but for older, it's toward the back of the vehicle. Not positive on this though.

I bet you put the teeth in the wrong way. I found a thread on Yotatech that I went by when I did this, look for that.

Will it go in at all if I faced the teeth in the wrong way? I have a 99 SR5 and I know I faced the teeth towards the front of the vehicle when I fed it. This is very important please confirm if anyone has a 99.

Mine did the same thing. I just assumed there was old white plastic in the motor that needed to be dug out so that the motor can correctly calibrate itself. Did you compare the tail on the old one to the new one? Have you opened the motor to check if there is white tail in there?

I just cut the tail off the old one and put it back on as a stop gap. I now have a manual antenna. Same as every car I had prior to about 1985. Who needs a whip mod? The antenna motor runs for ten seconds or so every time I turn the radio on or off--big deal.

Now that it is warm I'll soon be pulling the antenna to see if I am right.

Guys, I'm happy to report that the issue has been resolved. If you have the same issue as I did, make sure you buy the high quality OEM antenna mast. They are only a few bucks difference, made my day.

Here is the ebay seller I bought from which DID NOT work.
eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices

Here is the ebay seller I bought from DID work.
eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices

Both of them claimed their antenna masts work on 99 4Runner but the quality is totally different. More importantly, the real OEM mast is a little bit thicker than the after market one.

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Here is the one I bought that did NOT work:

Toyota 4Runner Antenna Mast OEM 86337-34030 Replacement | eBay

It says "Direct replacement for OEM" in the ebay description. So, it is not OEM. You make sure you get the real OEM mast to avoid unnecessary issues like I had. OEM is only $2 more.

Yeah, I got that. I'm just reinforcing your case. I'll try yours and report back.

A good lesson. Hopefully this will save someone some hassle down the line. Glad you got it worked out.

ouki is THE MAN. I received the new $18 mast from raderra (very fast shipping, by the way) and it worked perfectly. I got out my vernier caliper and measured thickness from top of teeth to back and got these results:

Cheapo e-bay mast tail: 3.5mm
Raderra e-bay mast tail: 4.2mm
Factory mast tail: 4.0mm

The piece of factory tail was what was left inside when I cleaned out the motor. It was visibly worn after 12 years, but still worked fine until it broke. It had zero flexibility--if you bend it at all, it breaks. Anyway, I figure it was probably 4.2mm when new.

So for anybody with this problem in the future, make sure your mast tail is at least 4.0mm thick. Buy a new mast from seller raderra on e-bay and avoid the cheap $12 ones all over e-bay.

Now we will see how long it lasts.

You are welcome! I'm glad I could be any help.
It's been two weeks since I fixed my power antenna. It comes in and out like new! Hope it lasts long.

My power antenna was broke when I got my 98 4Runner.

So I pushed it all the way in and hooked up my Sirius radio and antenna!

No power antenna issues any more!!!!