• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • Hey! Be sure to login or register!

Trim Assembly Overhaul Time

JDWilliams

Registered User
Looks like it’s time to rebuild the entire jack screw assembly on my PA12-150. Any recommendations on who to send it to for the work?

(I would have searched the topic before asking but the search function is locked up on me for some reason.)
 
depends on if you have ORIGINAL -12 trim system (one groove pullies) or updated dual groove -18 style pullies & cable....
 
I replaced both pullies front and gear original style and that fixed my trim issues. Groove was worn out to the bottom of both.

Doug
 
98% of the time a single cable trim is slipping , its the pulleys . One or both has its V grooves worn down to the bottom .......... They are now U grooved and will slip constantly. Getting lubrication onto the trim pulleys will certainly spoil your system as well. As Doug suggests; two new pulleys and a clean cable with proper tension does wonders for any "single groove system. Steve Pierces cleaver mod to the "idler tightner" of adding an extra pulley into the original tightner sheath, allows it to pull on BOTH sides of the wire equally, instead of just pulling one side over till its touching itself, so something in the order of doubling the effectiveness of the tensioner.
The double wire trim system is THE final answer no doubt , and should be done at recover. However a cleaned up single wire, riding high in new V grove pulleys that is correctly tensioned can work for years if properly maintained. Dont forget if the rear thru bushing on your stabilizer has corrosion in it binding the system up, a double pulley will slip as well???
MMS Mike has converted some over from single/ double with the fabric on
the plane, and knows all the tricks of the trade. However I would imagine if a mechanic has never done one before; you could easily double the labor bill; over a mechanic that already knows how its done........

I ferryed a Cub a few years back that was less than 10 hours out of an expensive inspection by a big shop in Maryland. Here is what I found wrong with it the moment I pushed it out.
Primer would not pull in fuel and leaked when full extended.
Brake diaphragms both soft so almost no brakes even though fluid was full.
Tailwheel totally out of adjustment and basically NON functional.
Tach slipping constantly, Airspeed reading 140 on initial climb out.
T&B laying over on a dogbox. Ampmeter snaping from charging 30 to discharging 30 constantly just like a wiper blade. Oil preasure below the yellow arc? Carb heat didnt work at all,
Up to altitude and leveled off, tryed to trim it out......... No luck. Had to hold forward against the tail for next 3 hours. Airspeed reading 60/65 , gps reading 105. '1hr out' both guages showed only 1/4 tanks...... 2hrs out it showed totally nothing? It was quite an interesting flight to say the least.
Landing it for the 1st time in a 10kt direct crosswind with no brakes and tailwheel basically unhooked, because the connector springs were compleately wrong for that airplane. Was a refreshing reminder of the tap dance and double shuffle of the rudder pedals to their extreame limits.
Other than that stuff, it flew like a dream!
2 weeks later into a " real inspection"
Everything had been repaired or replaced. Both pullys on the trim were totally worn out, had to be replaced.
The shop in Maryland had entered two pages of total BS in the books and had done really nothing except charge the customer $3k for an oil change and alot of fancy looking BS in a log book.....................
Good luck with your new double trim system, they work exactly like the single pulley does when they are both set up correctly, but twice as good as a single pulley that is slipping!!! Lol.
E


Sent from my LM-X210 using SuperCub.Org mobile app
 
I ferryed a Cub a few years back that was less than 10 hours out of an expensive inspection by a big shop in Maryland. Here is what I found wrong with it the moment I pushed it out..................................................................."
The shop in Maryland had entered two pages of total BS in the books and had done really nothing except charge the customer $3k for an oil change and alot of fancy looking BS in a log book.....................
Good luck with your new double trim system, they work exactly like the single pulley does when they are both set up correctly, but twice as good as a single pulley that is slipping!!! Lol.
E
That reminds me of a Taylorcraft 15 that I flew home after a rebuild and annual for a new owner. I hope that the owner of "your" Cub reported that annual to the FAA. We did on ours, the FAA was grateful as they had been after that IA for years. The IA lost his ticket. The aviation industry is dangerous enough without having this type of maintenance.

Edit: ps, That IA was an airline mechanic who did annuals out of the trunk of his car for some side cash.
pps: Just remembered his last name. Crook. How very appropriate.
 
Last edited:
Thanks for the great info. Decided to replace with the Dakota Cub assembly. It’s dual pulley already with the PA18 setup.


Sent from my iPad using SuperCub.Org
 
JD,
Great choice. I believe their jack screw is a finerpitch thread than the original
"Cast" yoke has. So it is going to be smoother. The Dakota CNC yoke, is light years
ahead of a Univar type. You made the right decission for sure.
Good Luck
E

Sent from my LM-X210 using SuperCub.Org mobile app
 
JD,
Great choice. I believe their jack screw is a finerpitch thread than the original
"Cast" yoke has. So it is going to be smoother. The Dakota CNC yoke, is light years
ahead of a Univar type. You made the right decission for sure.
Good Luck
E

Sent from my LM-X210 using SuperCub.Org mobile app

Dakota Cubs jack screw installed. Works great. Definitely finer pitch so more turns of the handle to achieve the same degree of trim change. Gives finer pitch trim control but takes longer to crank to the new setting when needed. Very pleased.


Sent from my iPad using SuperCub.Org mobile app
 
My trim cable and pulleys have 6700 hours on them. Always worked great. I shot some Tri-Flow on the jack screw in October, and the trim system stopped working in November.

I assumed the cabl or pulleys had finally taken a break. Not so - the jack screw and yoke were being held by a substance not unlike JB Weld. Cleaned it all off, applied engine oil as I have for almost six decades, and presto - a really well functioning trim system again.

Maybe there really is something to this business of compatibility of lubricants?
 
My PA20 single groove pulley system would freeze up when the temperatures were well below freezing... bought the old school cloth electrical tape...same stuff piper used to tape the wiring to the fuselage...tears like duct tape...fed a 1/4” wide strip into the pulley groove at the trim handle a couple three wraps. No more slipping


Sent from my iPad using Tapatalk Pro
 
Trim screws can fret-wear from vibration and asymmetric loads on the horizontals. Watch a Cub tail on takeoff shake like a dog passing worms (big engines and props are worse) and it's no mystery why the trim assembly wears and gets looser. Oil helps - LPS-2 and whatever - but temperature appropriate Moly additives (Molybdenum Disulfide based lube) in a grease can add an additional layer of protection.

Clean the trim parts periodically with a narrow long rag soaked with solvent. Wrap it fully around the screw (with trim up then down) and pull the ends in a sawing up motion and down the screw to clean off debris. After it dries apply lube of choice. Also lube the cross tubes that connect the front and rear horizontal stabilizers at their connections or fittings with grease or penetrating oil. Recent tubes are chrome plated and can resist corrosion.

Gary
 
Great advice Gary, and the friction tape is also a bandage for the problem. Of course a new front pulley with the unmolested V groove does wonders to fix 95% of them.
A friend of mine decided Piper screwed up trying to use existing tail brace wires on the 18 stabilizers. And felt it was a major culprit of excessive
"Tail Shake" so he had some longer ones made up that where attached out where they should have been in the 1st place, from memory about 7" outboard of factory holes. He flew it that way for years and claimed it was
A HUGE improvement over factory wires. I flew it for fun, and it had NOTICEABLY less shaking going on back there. Great mod if your experimental. SuprCrow has 4 wires on his tail and long flaps but his tail is nearly ROCK solid.
These new CNCed trim yokes are light
years ahead of the old cast ones. And the finer pitch thread gives a "lower gearing". Corrision in the rear tube bushings is pretty common and one old time Cub mechanic told me he has used nothing but Vaseline to lube them for years with stellar results.
Food for thought.
E

Sent from my LM-X210 using SuperCub.Org mobile app
 
SuprCrow has 4 wires on his tail and long flaps but his tail is nearly ROCK solid.
My Cub has the stock tail wire setup and the long flaps with a rock solid tail. I think that it is the long flaps eliminating turbulence from the outboard end of the stock flaps reaching the tail which does the trick.
 
My experience is even with flaps up, a full power climb out will make them shake pretty good. Most don't know that because it is really difficult to turn around and look - especially for older folk.

If you don't keep a drop of oil on the interface between stab and tube, you will have a difficult time getting them apart at overhaul. I pulled mine with great difficulty when the aircraft was 25 years old and had been covered twice. Now it is 63 years old and they slide right off. Vaseline sounds like a horrible idea- isn't it water soluble?
 
Of course you all knew about the young newly married mechanic who didn't know the difference between vaseline and window putty?

Yes, all his windows fell out.
 
Question: Does the PA-18 tail shake worse than the PA-12? I had both and it seemed like it did but can't exactly recall. If so maybe the flatter fuselage sides of the -18 create some of the turbulence on the tail. Or maybe it's fuselage truss design?

Didn't CG Taylor notice the fabric buffeting on the sides of the original Cubs he designed and then built the tapered side Taylorcrafts for better air flow along the fuselage and speed? May be an Urban Legend worth exploring.

Gary
 
Not sure if the 18 shake is more than the 12 or not? Can tell you for sure
the PA-20 feathers on a 12 have noticeable less than 18 feathers. They surprised me how well they work. Only place they seam to show much inferiority is when loaded heavy AFT on a hot day they will sag more.....
But for normal flying they work darn well. I had 18 feathers on my PA-11
But if I was doing it again I would probably look hard at PA-20 tailfeathers if there was good set cheap........
On a real nose heavy 12; then18 feathers would be mandatory.
Or if you were constanly hauling gross loads.
I am thinking the shorter the prop the less the shake back there?
The big long props just pushing more air around fuselarge?
E

Sent from my LM-X210 using SuperCub.Org mobile app
 
Recently picked up a 12 that someone gave up on the trim system & bastartized in an electric trim system, the good news is that the original system seems to be all there with the exception of the jackscrew pulley. I'm trying to go back to at a minimum the original 12 system, or better yet the 18 system. I've read that with some work it's doable on a covered plane though not exactly fun(Mike MCS I think was that poster) I have both new 2 groove pulleys, so going to the 12 system & only using one groove on each should be easy enough, but here is the question, does the standard 18 length trim cable work(once the added tensioner/idler pulleys are installed of course) or does it need to be a custom made cable?
 
Recently picked up a 12 that someone gave up on the trim system & bastartized in an electric trim system, the good news is that the original system seems to be all there with the exception of the jackscrew pulley. I'm trying to go back to at a minimum the original 12 system, or better yet the 18 system. I've read that with some work it's doable on a covered plane though not exactly fun(Mike MCS I think was that poster) I have both new 2 groove pulleys, so going to the 12 system & only using one groove on each should be easy enough, but here is the question, does the standard 18 length trim cable work(once the added tensioner/idler pulleys are installed of course) or does it need to be a custom made cable?

I don’t remember but I think the 18 cable works. We have a guy local the could make anything we needed


Sent from my iPhone using SuperCub.Org mobile app
 
As everybody stated above, mine slipped terribly and took the advice of this fourm. Replaced both pulleys and the cable which was no easy task. I bought the parts from Univair. My 12 has the extended baggage that was impossible to remove short of drilling out all of the rivets so everything was done blind through the inspection holes. The most heartbreaking task was we had to cut the fabric outside the trim crank to get the pulley off. We also had to cut the fabric in the cabin on the right side of the rear seat to get the cable routed, more fabric repair. Then the rear pulley was a lot of fun as the trim cable is almost too short. Again blind through the inspection hole and a lot of lost skin. The trim operates as it should and when it comes time to recover her I’ll certainly install the PA18 double pulley system.
 
Unless I'm missing something, don't you mean on the LEFT side of the rear seat? To my knowledge there is nothing trim related on the right side of the aircraft until you get back to the tail, then you might need to work thru both sides... Why did you need to cut next to the rear seat, is there a guide there that I've not seen yet? I have not seen an uncovered -12 and it is a totally different affair on the 20/22 that I have much more experience with...?!?

As everybody stated above, mine slipped terribly and took the advice of this fourm. Replaced both pulleys and the cable which was no easy task. I bought the parts from Univair. My 12 has the extended baggage that was impossible to remove short of drilling out all of the rivets so everything was done blind through the inspection holes. The most heartbreaking task was we had to cut the fabric outside the trim crank to get the pulley off. We also had to cut the fabric in the cabin on the right side of the rear seat to get the cable routed, more fabric repair. Then the rear pulley was a lot of fun as the trim cable is almost too short. Again blind through the inspection hole and a lot of lost skin. The trim operates as it should and when it comes time to recover her I’ll certainly install the PA18 double pulley system.
 
:oops: Everybody is in a hurry and likes to use pop rivets in the extended baggage before they cover the plane. I had an issue and had to crawl in and drill them all out. Bills Javron build is the way to do it.
DENNY
 
:oops: Everybody is in a hurry and likes to use pop rivets in the extended baggage before they cover the plane. I had an issue and had to crawl in and drill them all out. Bills Javron build is the way to do it.
DENNY

second? mechanic I worked under did very deep annuals... interiors came out, seat base came out.... was a pain, but he didn't pencil whip a thing.... overkill...

so I'm kinda a screwed in interior guy because of that... still....
 
I should proof read my post lol. your right the left side. It has to be cut in order to feed the cable through the Farrell leads ( I can’t spell either). I flew out to see Steve Pierce to confirm before my mechanic took
a knife to it. Bottom line the trim works perfect.
 
In actual fact alot of the hype about the double pulley system and basically condeming the standard single wire original set up needs to be reviewed with care. In reality if you carefully clean the rear jack screw and pulley and trim wire,
And simply replace the Front pulley with a new one with the correct V groove it will
restore about 90% of the slipping you may be having. Proper tensioning of the wire is important and Steve Pierce has a very cleaver mod that adds a pulley to the existing bracket that then pulls on BOTH wires at same time. A perfectly clean system, with a new V groove up front, combined with a properly tensioned wire, will get you back up and going in almost every case. Converting to the 18 system is a great option at rebuild time, but not so much unless, all the above won't cure it.
E.

Sent from my moto e5 go using SuperCub.Org mobile app
 
Last edited:
98% of the time a single cable trim is slipping , its the pulleys . One or both has its V grooves worn down to the bottom .......... They are now U grooved and will slip constantly. Getting lubrication onto the trim pulleys will certainly spoil your system as well. As Doug suggests; two new pulleys and a clean cable with proper tension does wonders for any "single groove system. Steve Pierces cleaver mod to the "idler tightner" of adding an extra pulley into the original tightner sheath, allows it to pull on BOTH sides of the wire equally, instead of just pulling one side over till its touching itself, so something in the order of doubling the effectiveness of the tensioner.
The double wire trim system is THE final answer no doubt , and should be done at recover. However a cleaned up single wire, riding high in new V grove pulleys that is correctly tensioned can work for years if properly maintained. Dont forget if the rear thru bushing on your stabilizer has corrosion in it binding the system up, a double pulley will slip as well???
MMS Mike has converted some over from single/ double with the fabric on
the plane, and knows all the tricks of the trade. However I would imagine if a mechanic has never done one before; you could easily double the labor bill; over a mechanic that already knows how its done........

I ferryed a Cub a few years back that was less than 10 hours out of an expensive inspection by a big shop in Maryland. Here is what I found wrong with it the moment I pushed it out.
Primer would not pull in fuel and leaked when full extended.
Brake diaphragms both soft so almost no brakes even though fluid was full.
Tailwheel totally out of adjustment and basically NON functional.
Tach slipping constantly, Airspeed reading 140 on initial climb out.
T&B laying over on a dogbox. Ampmeter snaping from charging 30 to discharging 30 constantly just like a wiper blade. Oil preasure below the yellow arc? Carb heat didnt work at all,
Up to altitude and leveled off, tryed to trim it out......... No luck. Had to hold forward against the tail for next 3 hours. Airspeed reading 60/65 , gps reading 105. '1hr out' both guages showed only 1/4 tanks...... 2hrs out it showed totally nothing? It was quite an interesting flight to say the least.
Landing it for the 1st time in a 10kt direct crosswind with no brakes and tailwheel basically unhooked, because the connector springs were compleately wrong for that airplane. Was a refreshing reminder of the tap dance and double shuffle of the rudder pedals to their extreame limits.
Other than that stuff, it flew like a dream!
2 weeks later into a " real inspection"
Everything had been repaired or replaced. Both pullys on the trim were totally worn out, had to be replaced.
The shop in Maryland had entered two pages of total BS in the books and had done really nothing except charge the customer $3k for an oil change and alot of fancy looking BS in a log book.....................
Good luck with your new double trim system, they work exactly like the single pulley does when they are both set up correctly, but twice as good as a single pulley that is slipping!!! Lol.
E


Sent from my LM-X210 using SuperCub.Org mobile app

Do you have contact info for Mike? I am in need of skills for my slipping PA-12 trim. My regular shop isn’t experienced in doing new trim with fabric on.

Troy
 
Back
Top