Notes on Stabilator Trim Cables - JW, Gilbert and Steve Pierce, Homer, Zig

Well, it's not as easy to deal with the cables as it is clipping your fingernails, but it's not too bad. 
First thing getting started is open the zipper above the Pilot's seat and let down the spring that 
tensions the trim cable. I usually just loosen the clamp and slide it back so the spring sags and 
makes it as slack as I can get it. You MAY be able to take the spring off completely, but it's a 
difficult place to work in! It may very well be MUCH harder to get it back hooked up than to get it off.
 All you need is a little slack to work with back at the jackscrew. MAKE SURE you got a "handle" 
on how the actuating cable runs on the rear double-sheave pulley before you let it go slack. 
That's a toughie to figure out if you "drop" the cable(and even harder to tell you how to do it 
in the forum). Don't let this scare you. The job sucks, but it'd not really that difficult to accomplish. 
Another tip, make sure that the cross tube that the stab mounts to (on the jack mechanism) 
doesn't get installed the wrong way "over center". Memory tells me it has to be swung UP, ABOVE 
the pivot point, and it wants to flop down below the pivot (I think?) if left to its own means. 
Just note before disassembly which way that crosstube sits (again: I think its tilted up). 
See, if that tube is the "wrong way to", it all goes back together just hunky-dory, 
but it won't move up (nose down position) very far before it binds. Only thing is you have to 
basically do the whole disassembly/reassembly thing with the stabs again to turn that tube 
to the right position. When finishing up the job, last thing is to retension the spring over the 
pilot's head. Get it tight enough to not slip, but if its too tight, the trim is difficult to operate. 
That part is trial and error. Don't forget, this requires a signoff. The Inside Man will DEFINATELY 
require a full-time assistant on the outside to "gopher" stuff. You only want to go back in there ONCE!


 
My 63 Colt also had a spliced cable and I could turn only eight turns with the crank before
 it would jam. I also got a new stainless cable for $100 from Cesare. 
Beautiful job on the splice and fast service, I highly recommend him.
On the replacement, not an easy job, but it can be done with the fabric in place. 
The depiction of how it is wound around the pulleys is found in the "Drawings" CD. 
It is simpler to make a visual inspection and mark it on paper as to how and which side of 
cable goes in which groove. 
Start by disconnecting the tersioner spring loop, to the left of the trim handle. 
Also drop elevator and remove horizontal stabilizers at the back, for easier access to the 
trim jack screw assembly. (The stabilizer pivot stub shaft at the back may be seized in the truss, 
how to remove it is another story.) There are two small pulleys (about 1 inch dia.)
 about a foot forwards of the Jack screw. Slack off the supporting bolts, 
but do not remove,same with the other supporting pulleys, so that you can get the cable past 
the guards. On top of the Jack screw, is a Castellated nut, secured with a cotter pin. 
Remove the cotter pin and the nut ( 9/16 socket, hold the pulley from turning ) and spacer washers. 
Now you can drop the jack screw sufficient to unwind the cable over the top of the pulley. 
You will have to remove the Baggage compartment back cover, interior light and radio speaker. 
Trim handle, indicator plate and spring. Also you will have to make a cut in the headlining from 
trim plate slot to handle pin for access.
There is a curved pin, securing the double pulley to the handle shaft, you have to drive it out to 
be able to remove the shaft upward, remove the pulley and unwind the cable. You have to cut 
a small, 1/2 inch dia hole in the fabric, just above the shaft to be able to remove the shaft and 
separate the pulley. ( Wag Aero sells a rubber plug as a wing strut attachment inspection 
cover. $1.50 , fits perfectly) There is one more problem area, there is a "stand off" 
about 3 inches high, a little aft of the baggage compartment. It secures the top stringer with 
a small sheet metal screw to the stand off and fuselage truss. (Thanks Mr. Piper for using a screw) . 
The cable goes on each side of the stand off, there is no other way than to force the stringer and 
fabric up to pass the cable over the stand off. It was not easy, but I managed it. 
You have to work through the Zipper holes too.   I made a 1/2 in plywood panel that fits just aft of 
the baggage compartment on the truss tubing, so that I could sit on something, 
without danger of slipping and damaging the fabric.   Have fun, it can be done.

Merle; here's a couple things to check. Access the trim actuating cable from inside the rear fuselage. 
Take a clean (preferably white) rag and slide it along the trim actuating cable. You should be "some" 
staining on the rag, but you should NOT see what you would expect when doing the same thing to a 
"well-lubricated" control cable. This cable is NOT supposed to be "well lubricated", and a 
"well lubricated" jackscrew will sometimes mean a lubricated actuating cable, as well. 
If the cable has been greased, clean it thoroughly with solvent degreaser on the rag (for it's entire 
length- it's a "continuous cable" and may migrate along it's path. If the cable appears pretty dry 
(which it should be), then you MAY be looking at a worn jackscrew. With the trim in the nuetral 
stab position (not halfway between the "slot" up and down, but with the elevator in trail with the stab),
 how much "up and down" movement do you have if you grasp the leading edge of the stab right next
 to the fuselage and "wiggle" it up and down? Be "firm" in trying to make it move, but don't go crazy...
you don't need a hydraulic jack for this test. Anything more than just a wee bit of noticeable movement
 is basically "too much", and the jackscrew (and the yoke) are worn. 030" slop is a "bad one". 
Any more than "just noticeable" is "worn". (These numbers are just a rough guestimate; there
 are no "published" limits.) Any flight load will tend to "force" the screw threads together and 
lessen the pitch effect of the thread and thereby partially bind the mechanism when it's loaded. 
"More grease" does not cure this-ever. But if neither of these items is really obvious, you may
 just have a "loose" spring on the tensioner (idler) pulley overhead the headliner. To adjust for 
more tension, loosen the screw that secures the Adel clamp where the cable to the spring is 
attached (around the fuselage frame diagonal tube overhead) and slide the clamp (with spring attached) 
a little further AWAY from the pulley that the trim cable goes through (the idler), then lock it down again. 
This will add tension to the spring and cable. There is a REAL fine line between too tight
 (causing high drag on the system and hard operation) and too loose (causing slippage). 
I tell you that LAST because it is not the "fix" if the other two factors are in play. Note that if the 
airplane is not "as built" from the Factory, it originally had friction tape UNDER the clamp to prevent 
chafing on the tube and helping to prevent slippage. Since friction tape is not anhydroscopic,
 at lot of people don't like to use it on rebuilds. I like 3M fibreglas electrician's tape there because 
it is the best of both worlds. If NOTHING is under the clamp, it will usually migrate towards the 
pulley (loosen) over time. You say the problem "recurs". That wouldn't be when the OAT comes
 down (either seasonally or at higher altitudes), would it? If so, and depending on "severity", you 
could just have a wrong grease on the jackscrew. SOME greases get stiffer'n-a-you-know-what 
when it's cold. Particularly "long grain" axle bearing greases, which a lot of people use because 
THAT'S what they keep in their greasegun. The above problems should all be relatively "constant",
 not intermittant. Let's hear what you find. John 

 
Allow me to "bring up the rear" relative to the horizontal stabalizer. The horizontal stab is two 
separate pieces that are connected at the rear via a 12 inch or so pipe going through a tube 
assembly which is welded to the rear most part of the airframe. When you trim the stab, the 
jackscrew is moving the front up and down and the rear stays put but pivots by the pipe
 turning inside the tube. That is the theory, however during the disassembly of my plane 
for new fabric, I found the connecting pipe effectively frozen to the inside of the tubing, 
by gunk and corrosion. Instead of it smoothly rotating, I could barely move it. It took about
 a half of a can of "mouse milk" and a whole lot of twisting and pulling to get it free, and I 
could have used the strength of the Governor of California in my efforts to pull it out after
 I finally got it freed up. Anyway, as I think back on the flying we did, I recalled an
 inconsistency from flight to flight to the "feel" of trimming. I can now understand the
 problem, I was having to overcome corrosion friction to move the horizontal stabalizer 
around it's pivot point. So, take a look back there while some one else is trimming, and see if
 you can identify it binding. Put some oil on the shaft while it is turning to keep it lubricated. 


I kinda sorta ran across a note in the Tail Assembly drawing the other day that might lend 
some clarification as to what is good and bad. As John said "just a wee bit of noticeable 
clearance". Piper felt that .015" of clearance was just a wee bit.

According to Piper Drawing, Tail assembly 11825 Note 2: ".015": maximum vertical play allowable 
between stabilizer & adjacent fuselage structure."

Like Homer I found the rear liner tube frozen in the horizontal stabilizers. When I finally 
got it out I found it was piece of common tubing someone had substituted in years past 
for the Piper Liner Tube that is chrome plated and precision ground. Again on the same 
drawing, Fig1 indicates that tube should have running fit with with the rear support and a 
max clearance of .006". I am welding a grease zerk into the rear support fitting which 
incidently I had to replace due to extreme corrosion and wear.
Like the rest of you, my inability to trim intermittent. I kept the jack screw scrupulosly 
clean and lubed with light oil. The rear liner tube and support was the problem. 


When I rebuild a fuselage I weld a 1/4 x28 nut over the hole and then screw in a grease zerk. 
Building a better mouse trap. Keep oiling that hole cause it does creep through there. 
A good pentrating oil helps too like Aero Kroil