Mystery Vibration - 74 Cherokee 140

The Visitor wrote:
: Just a wild guess but could a control cable, like the elevator cable be
: popping out of place around a pulley somewhere. Or the rudder? I am
: thinking that perhaps with that happening a surface might be free to
: vibrate because the tension is not what it should be.

Since you had a relationship with forward yoke pressure and the vibration,
check the stabilator. The bearings/bolts that hold it on are subject to wear and
corrosion... I replaced the two on mine. Grab the end of the stabilator and try to
pull it back/forth and up/down (without rotatating). It should not move at all... no
"tick-tick" back and forth.

Mine weren't too bad, but the bolts had a bit of rust and a slight wear on
them. Just to provoke respect for this oft-ignored point of wear on PA28's....
exactly two 1/4" bolts are what pivot the stabilator and hold the whole thing on.

Other things to check back there are the trim surface. We had to replace ours
due to cracks where it connects to the arm that actuates it. There's also a bushing
in the bottom of the trim jackscrew.

Just some random thoughts... doesn't really sound like engine stuff.
-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************