The power antenna on my 1981 300D has become intermittent in it operation and does not always extend. When it does not it seems that you can hear the motor running (extend and retract).

The antenna mast is very clean and recently lubricated. If you manually extend the antenna after it fails to extend electrically, it will always retract electrically.

Seems to me that this is mechanical, not and electrical issue. Perhaps the mast extending track is slipping? Any thoughts on the best options? Thanks.

__________________
2012 B Class

1981 300D - Now with greazzer

Have you checked the nylon/plastic core? Maybe broken, maybe worn, maybe gunked up.

Can you remove the mast/core with the antenna retracted and powered off?

I was thinking that it could be pulled out with the power off and then replaced by threading it and retracting the antenna.

__________________
2012 B Class

1981 300D - Now with greazzer

Assuming that you have the Hirschmann 6000u, which is the unit with the big metal case, there's a pinch roller inside that presses the nylon driveshaft in the mast against the big takeup reel that provides the up/down motion. The roller in the pinch roller component can seize, which can prevent the mast from going up and down smoothly. Also, the serrations on the takeup wheel can grind down points along the nylon shaft when the mast is stuck and the takeup reel turns against it. So if you open the case or remove the mast, wear points along the driveshaft are a definite sympton of a frozen pinch roller.

I believe a replacement pinch roller mechanism is NLA, but it's easily repairable. You can take the pinch roller component apart and replace the roller with a bearing of similar size.

Check the wiki, there are are few threads, button in the upper right corner:

http://www.peachparts.com/Wikka/DoItYourSelf

Pics from my antenna repair show the innards, so you've got some idea of how it works:

http://www.peachparts.com/Wikka/W123AntennaMast2