Nose gear shimmy + lubrication AD

[AlexLev]

Was in the shop yesterday to check preload and lube flight controls. What a PITA to do multiple times a year when you fly more than 100 hours a year.

I mentioned to the shop that I had a slight nose gear shimmy very occasionally and they did some stuff to the nose gear, lubricated various parts of it...and now the shimmy is way worse. Any idea on what could have caused this? The shop seems to think a new tire or a balance of the nose gear tire could fix it. Do Mooney's have a shimmy dampener? Just looking to educate myself on the issue.

Looking back in the logs, before I bought the plane back in 2008/09, about 1000 hours ago, I see this: ""Replaced nose gear truss with repaired supplied by Lake Aero Styling. Replaced nose gear pivot truss with repaired. Installed new nose gear steering horn. Installed M20-202-001 nose gear tracking kit."

As an aside, I'm sure the 100hr lube AD has been discussed a lot, but I'm curious, what do you guys pay to have it done? How do you handle it? I just recently started using a new shop and it was our first time working together on this. I removed and reinstalled the three piece belly myself, but they still charged me 5 hours of labor to do the gear lube, preload check, etc which seemed a bit on the high side to me. Was not a great experience to be dinged for 5 hours of labor and then land with a dramatic worsening of the shimmy, especially when I did all the dirty work of r&r'ing the panels.

Edited June 5, 2019 by AlexLev

[steingar]

Isn't there a bushing you can get from LASAR to stop the shimmy?

[TTaylor]

When was the last time your gear doughnuts were replaced?  I have found old ones can contribute to shimmy.

[hypertech]

Is this an MSC?  I've had various issues with my nose wheel tracking since I got the plane and it too had a new truss installed just before sale.  Most of the "shimmy" was in the steering horn and Lasar does offer a rebuilt one.  I got a lot of that out with my local mechanic.  But the tracking problem *seems* to be related to a washer / spacer I was missing.  When I had the pucks done at the MSC, they discovered the missing spacer and installed it.  It moved the nose gear significantly - far enough that I need to adjust by sidewinder tow bar because its now too low to comfortably hold when on the plane.  If the nose gear isn't trailing right, it can dart off on you.  I would suggest this is one of those areas where a specialist that knows what a Mooney is supposed to look like is worth the effort and cost to get it to the MSC.

[David Lloyd]

Shimmy and tracking problems are most likely two issues related by the nose gear.  First, good the steering horn has been recently replaced.  Download from this site a copy of the Mooney Maint. Manual.  Read everything about shimming the steering horn and lubrication.  Get your mx to read it.  Search this site.  Just last week one of our knowledgeable contributors wrote about lack grease wearing things and then needing shims.

Other issue mentioned was tracking.  Don Maxwell's site, read about SB202 and the 8 second ride.  http://donmaxwell.com/the-eight-second-ride-sb-m20-202/  If you wonder if you have this problem after reading about it, you don't.  Many years ago I kept having my steering worked on by a supposedly knowledgeable mechanic.  Replaced the steering horn, shims, rod  ends and I continued to have problems.  Lost control of the airplane in Odessa, TX one windy morning.  Gez, I was only rolling about 20 mph and could not control the nosewheel.  Couple weeks later in Richmond, VA I broke the steering torque tube trying to control it.  Then I read about SB202.  Like a new airplane within a few days.

[AlexLev]

Just to answer some questions:

1) Yes the shop I went is an MSC, although I'll be honest. The two younger kids they put working on my plane to lube the gear exclaimed they have never seen a J-bar Mooney and couldn't believe a Johnson Bar Mooney existed. They went into the cockpit and played with Jbar for a while. I prob got billed for them playing with it too, ha. I found it a little surprising that an MSC has never seen a Jbar Mooney. I suppose they get more business from the Acclaims, newer models, etc and all the vintage owners prob do their own work in supervision with an A&P (which is a place I'd love to get to).

2) I believe it has been a while since the shock discs needed replacement. I asked my shop during annual if the discs were still good and they said they were...so I deferred the item, but it's possible they never really measured them the way outlined in the service manual. That could indeed be the issue.

[steingar]

Hard to believe an MSC never saw a J-bar.  Mooney made more C's than the rest of the models combined.

[Davidv]

I’ve only owned a Mooney for a short amount of time but in my dealings with two separate MSCs it doesn’t sound very surprising.  The shops I’ve been to are also service centers for cirrus, Cessna, ect... When you look at the amount of Mooneys being producted vs other brands we are sometimes a small part of their business (also the the A&Ps come and go).  I also had this vision of an MSC of this ultra specialized shop where I would see nothing but Mooney tails and it turned out mine was the only one in the hangar! Maybe at Don Maxwell and some MSCs around the country but at least not the ones I’ve seen in person.

[Shadrach]

Firstly, make sure the nose gear tire is at spec pressurization. Low tire pressure can cause shimmy at taxi speeds. It reads like a lot of the gear has been renewed. Is there slop in the steering (excessive dead spot on center)?  If the shimmy is worse it’s possible they adjusted some of the positive caster out of the nose wheel (not good). 

Incedently, lubing controls and checking preloads should be a quick and easy service. Firstly do the lube yourself. Two guys should be able to jack, check preloads and return an aircraft to service in about an hour.

[MIm20c]

The shop needs to keep the lights on and the employees need to feed their families. A simple oil change is probably around $165 in labor and takes an hour. I have my prop checked every 100 hours for $200 which takes him 5 mins standing at the prop. That’s $2400 an hour if you take it to the extreme. However, if you look at overhead, drive time, or liability exposure the number is far less. 

[Skates97]

2 hours ago, AlexLev said:

Just to answer some questions:

1) Yes the shop I went is an MSC, although I'll be honest. The two younger kids they put working on my plane to lube the gear exclaimed they have never seen a J-bar Mooney and couldn't believe a Johnson Bar Mooney existed. They went into the cockpit and played with Jbar for a while. I prob got billed for them playing with it too, ha. I found it a little surprising that an MSC has never seen a Jbar Mooney. I suppose they get more business from the Acclaims, newer models, etc and all the vintage owners prob do their own work in supervision with an A&P (which is a place I'd love to get to).

2) I believe it has been a while since the shock discs needed replacement. I asked my shop during annual if the discs were still good and they said they were...so I deferred the item, but it's possible they never really measured them the way outlined in the service manual. That could indeed be the issue.

I'm just wondering if you can get in trouble for paying someone to play with your Johnson Bar...

[jaylw314]

56 minutes ago, Skates97 said:

I'm just wondering if you can get in trouble for paying someone to play with your Johnson Bar...

<groan>  I was wondering how long that would take 

[rbridges]

mine shimmied on landings.  It was the steering horn. Got a replacement from LASAR,  If that's the case with you, I believe they sell a more sturdy version which may be a better option given how much you fly.

[DXB]

Regarding the 100hr ADs, it's my understanding the gear pre-loads don't really change much once correctly set, so the 100 hr AD is unfortunate for those  - maybe someone knows the history on how that became required so often but I don't.  My shop that does most of my annuals as found a way to test pre-load and sign off the AD without owning the gear rigging tools   When the 100 hr interval comes up before annual, I take it to my local MSC to get it checked properly.  They charged me 3 hours labor for lubing the rod ends and the gear work under the AD last year, and that shop is not known for low cost work.  Honestly, dropping and re-installing the belly panels is the ONLY time consuming part of this job assuming the gear preloads are in spec. Maybe the kids in your shop were learning on the job, or simply playing with their own Johnson Bars for a few of the billed hours .

Edited June 5, 2019 by DXB

[Prior owner]

You've got a 1000 hours on a rebuilt steering horn- maybe that's how long it takes to wear until out of limits? Play in the steering horn is easy to detect by lifting the front wheel off the ground- start moving the wheel around after it's jacked up- you'll see where the play is. There is a rod end with a very short extension bolted to the top of the steering horn that wears- look for play in that.

The tracking kit is nothing more than a washer under the retaining collar on the shock strut that moves the wheel closer to the airframe, dropping the nose of the plane. 

I'd have your nose wheel dynamically balanced- that's the easiest thing to rule out.

[Hank]

Shimmy can be caused by having the spacer installed backwards. It's not flat, it's tapered. Search Maxwell's website for details, this is not a problem that my Mooney has so I only know what I've read (exhaustively).

[cliffy]

Shimmy?

Tire pressure 1st

Caster- there is a SB that shows how to drop a plumb bob and see where the axle sits fore and aft

Check the torque on the big vertical steering bolt - there's a SB on that also

Raise the nose wheel and check play fore and aft and left to right (steering direction) Fore and aft will be wear in the big bolt bushing (LASAR has a fix), turning the tire right and left with more than a few degrees of loose movement means the linkage at the top of the nose gear is worn and needs work. 

That's all there is to it.  

[carusoam]

Mid-week power of MS is awesome!

Best regards,

-a-

[Shadrach]

5 hours ago, DXB said:

Regarding the 100hr ADs, it's my understanding the gear pre-loads don't really change much once correctly set, so the 100 hr AD is unfortunate for those  - maybe someone knows the history on how that became required so often but I don't.  My shop that does most of my annuals as found a way to test pre-load and sign off the AD without owning the gear rigging tools   When the 100 hr interval comes up before annual, I take it to my local MSC to get it checked properly.  They charged me 3 hours labor for lubing the rod ends and the gear work under the AD last year, and that shop is not known for low cost work.  Honestly, dropping and re-installing the belly panels is the ONLY time consuming part of this job assuming the gear preloads are in spec. Maybe the kids in your shop were learning on the job, or simply playing with their own Johnson Bars for a few of the billed hours .

Why are the dropping belly panels to check preloads?

[DXB]

7 hours ago, Shadrach said:

Why are the dropping belly panels to check preloads?

I thought it was needed for the   lubrication portion of the AD, not checking preloads - but correct me if I’m wrong - if not even 3 hrs labor seems like too much

[Shadrach]

58 minutes ago, DXB said:

I thought it was needed for the   lubrication portion of the AD, not checking preloads - but correct me if I’m wrong - if not even 3 hrs labor seems like too much

You may be right as the AD specifies “flight control systems” which could be interpreted as every moving part from the input (yoke and peddle) to the control surface. It’s a poorly written and I think impractical AD.  I’ve never had to deal with it as the plane has rarely flown 100hrs a year. My experience with the internal controls systems is that they hold their lubrication well and being unexposed to the elements should be lubed on calander time, not time in service. 

[Guest]

From the AD, lubricate ALL flight control and landing gear rod end bearings.  That is a fair bit of opening and closing of the airplane to comply with the AD.

(a) Within 25 hours time in service after July 10, 1972, unless already accomplished within the last 25 hours time in service, and thereafter at intervals not to exceed 12 calendar months from the last inspection or 100 hours time in service from the last inspection, whichever comes first, lubricate all flight control systems and landing gear system rod end bearings with a silicone spray lubricant or with an FAA approved equivalent lubricant.

Clarence

[Igor_U]

8 hours ago, M20Doc said:

(a) Within 25 hours time in service after July 10, 1972, unless already accomplished within the last 25 hours time in service, and thereafter at intervals not to exceed 12 calendar months from the last inspection or 100 hours time in service from the last inspection, whichever comes first, lubricate all flight control systems and landing gear system rod end bearings with a silicone spray lubricant or with an FAA approved equivalent lubricant.

Clarence

Yeah, if you do this during the annual, it doesn't really cost you much (time) as plane is already open.

I really don't think 5h is unreasonable and I believe I was charged something like that years ago. Since then, I do owner assist annuals and maintenance and believe me, I spend more then 5h to open and close all the panels necessary. Lubricating and greasing will add more time as well...

Over last decade (or more) that I am doing owner assist maintenance I have learn one thing:

No matter what quote for labor I get, I would think it’s high but takes me more time to complete it myself. I told my IA that few times.  YMMV.

 

Edited June 7, 2019 by Igor_U

[cliffy]

Don't forget that a gear retraction test AND over center torque check WITH the specified rigging tools is also required at the same time. If you or your A&P don't have the tools you can't sign off the AD

c) At the next lubrication as required in (a) and thereafter at the same interval as specified in (a), perform a landing gear retraction test and check the landing gear rigging. Information regarding rigging and torque preload may be found in Mooney Service Bulletin No. M20-35A dated 7-11-60 for Models M20 and M20A, Mooney Service Instruction No. M20-32 dated 11-3-72 for other models or later FAA approved revisions. Special tools supplied by Mooney Aircraft as noted in the reference documents or FAA approved equivalent tools are required for proper preload rigging. 

This means jacking the airplane!

Edited June 7, 2019 by cliffy

[AlexLev]

Update: Took it to Weber and they installed a few shims, which I think corrected the problem.