Nose gear shimmy

[steingar]

I did a flight with my CFI today. Landing at 3W2 I encountered a fairly violent nose gear shimmy on rollout, it dissipated taxiing in. I though perhaps I’d hit and imperfection in the runway and didn’t give it a second thought.  There was no abnormality in the subsequent takeoff, but I encountered the same shimmy on landing back at home base.  Again once I slowed down it went away completely. The tire is fine and at 30 psi.  I can’t see anything obviously wrong with the gear. Sound familiar?

[cctsurf]

There are a number of things that can cause this.  Here's the ones I'm familiar with:  There is another thread on the nose wheel part number that is considering this currently, their problem seems that it could be a worn out steering horn.  It could be that your gear needs to be shimmed so that it turns correctly.  http://www.donmaxwell.com/publications/MAPA_TEXT/M20-202 - Eight-Second Ride/EIGHT_SECOND_RIDE.HTM

[Bartman]

I had the same thing and could feeel it in the brake/steering pedals on landing. When we jacked it up there was lots of movement and slop in the nose gear. A new steering horn and nose truss rebuild from @LASAR fixed my problem. 

[ziggysanchez]

I'm replying to this thread because I'm interested in everyone's thoughts as I have also developed a shimmy in my nosewheel recently. Took it out to Maxwell and they found nothing out of the ordinary. My problem seems intermittent.

[cctsurf]

 

Just now, ziggysanchez said:

I'm replying to this thread because I'm interested in everyone's thoughts as I have also developed a shimmy in my nosewheel recently. Took it out to Maxwell and they found nothing out of the ordinary. My problem seems intermittent.

I find that it is highly related to landing speed and tire pressure.  Since I put a new tire on front, I've not had problems with shimmy.  I've also learned not to land at airline speeds...  I wipe my speed off in the flare and if I can I keep the nose gear off of the ground for a bit for a wheel landing...

[ziggysanchez]

Just now, cctsurf said:

 

I find that it is highly related to landing speed and tire pressure.  Since I put a new tire on front, I've not had problems with shimmy.  I've also learned not to land at airline speeds...  I wipe my speed off in the flare and if I can I keep the nose gear off of the ground for a bit for a wheel landing...

Mine happens while taxiing and sometimes as I'm slowing down after landing. I'm always over the numbers at 70 and usually touch down at pretty slow speeds. I always taxi a little fast but nothing that I would consider excessive. They pulled the tire at Maxwell, checked and repacked the bearings, made sure the tire was on the wheel properly and that it was inflated as it should be. It's a newish tire and has lots of tread. They did say that there was a little slop in the gear but nothing that should cause this issue.

[Shadrach]

Check that tire pressure is 49psi before you start replacing parts. 

[Sabremech]

12 minutes ago, Shadrach said:

Check that tire pressure is 49psi before you start replacing parts. 

Depends on the model. My C is 30psi. Any more and it does shimmy a bit.

[Shadrach]

47 minutes ago, Sabremech said:

Depends on the model. My C is 30psi. Any more and it does shimmy a bit.

Interesting. Mooney added 19 extra PSI to the nose wheels for 40lbs more on the nose. Some of which is off set due to the longer tail. What's more is the notion that it shimmys more in a C if over inflated and the opposite happens in my F. Bigger contact patch equals more shimmy. Over filling might do the same, but I've never overfilled.

Edited November 12, 2017 by Shadrach

[MARZ]

I get an occasional shimmy - gear is tight and a short dance on the rudder pedals eliminate it on rollout.  

[TTaylor]

I had occasional shimmy before I replaced the gear pucks.  No issues since.

[N201MKTurbo]

The Laser oversized nose gear bushing will do wonders. It is reasonably priced and not too hard to do. Put the reemer in a vice and spin the truss onto the reemer.

Jack the plane up and grab the nose wheel and see how much it moves fore and aft. It shouldn't move at all. If you pull it foreword real hard you will extend the overcenter link. That is not a problem.

A tight steering horn will hold a sloppy pivot bushing in place but it is just masking the problem. If the pivot is tight a sloppy steering horn will just give you sloppy steering.

It never hurts to do them both. Especially if you have the original steering horn.

Edited November 12, 2017 by N201MKTurbo

[steingar]

Bit of an update. I honed in on the pressure posts, as I had just topped up the tire and thought perhaps I’d overdone it. Deflated it to 25 psi and tried again. No joy. So much for the simple fix.  I’ll be on the phone to my mechanic. In two weeks the aircraft is supposed to go in for a panel upgrade (IFR GPS, new radio and ADSB transponder) and I may have it addressed there. We’lol see. My thanks to everyone on such sage suggestions.

[takair]

A quick way to see how tight your nose gear steering linkage is, is to grab the rudder and see how much free play it has.  I forget the specification (best look it up for actual value), but for practical purposes, if it moves more than about 1/2” each way, then it is worth further investigation and can cause shimmy.  

The older aircraft had an inferior steering linkage.  After repairing mine a number of times, I finally upgraded to the LASAR STC linkage, which seems to be holding up well.  Of course, all of the above mentioned areas can cause or contribute as well.

[neilpilot]

Maybe this has already been mentioned.  Is there an easy way to elevate your nose gear off the ground and hand rotating your wheel to check for a balanced rotation?  Could the tire & wheel be the source of the shimmy?

[steingar]

No play in the rudder that I can find. Might have to give LASARCa call and see how bad the damage will be to my wallet.

[Rwsavory]

How old is your tire?  We had the same issue, and it was solved by installing a new one.

[steingar]

10 hours ago, Rwsavory said:

How old is your tire?  We had the same issue, and it was solved by installing a new one.

Something to look into.  Deflating the tire a bit did dampen the vibrations some.  That said, my poor airplane did suffer a prop strike from its ham-fisted pilot (described elsewhere on this site).  I wouldn't be a bit surprised if the nose gear is a bit out of register.

[rbridges]

I had identical symptoms.  Shimmy that was very pronounced with speed.  Seemed to be worst on landings.  I'm guessing since more weight on nose wheel at higher speeds vs take off.  

Anyway, it turned out to be the steering horn.  Had a rebuilt unit from LASAR installed.  I'm wanting to say around 1 AMU with unit and labor.  They will charge you for a core until you send yours back to them.  I did notice the amount of play in the rudder decreased noticeably.  Didn't seem extreme prior to changing the horn.  Maybe 1-1.5 inches of play.  Decreased to roughly half.

[rbridges]

10 minutes ago, bluehighwayflyer said:

Exact same here, except that my shimmy was most pronounced when braking. I went from almost 2.5 inches of play in the rudder, stop to stop, down to around .75 inches. I don't think that there is a rudder play specification in the maintenance manual, but it is a darn good indicator. Call Dan at LASAR and he will send you what you need, including a couple of inexpensive heim bearings for the nose gear steering that are apparently also usual suspects. 

yep, you actually were the one that made the diagnosis for me.  Saved me and my IA lots of aggravation trying to find it ourselves.

[cctsurf]

CB question, Lasar will supply the steering horn rebuilt, does anyone supply the bushings to do the rebuild?

[Andy95W]

LASAR has those also.  In addition, they have their own PMA'ed oversized bushings for just about every landing gear part, as well.

BTW- they are also cheaper than the Mooney factory parts (which they carry too.)

[Bartman]

2 hours ago, cctsurf said:

CB question, Lasar will supply the steering horn rebuilt, does anyone supply the bushings to do the rebuild?

We just removed and sent my steering horn and nose truss to LASAR. They rebuilt it with new discs, upgraded bushings, and sent it back with the upgraded steering horn.  I'm thinking it was something like 2,500 all included, can't remember exactly, but it was not bad at all.

[mooniac15u]

On 11/11/2017 at 5:10 PM, steingar said:

I did a flight with my CFI today. Landing at 3W2 I encountered a fairly violent nose gear shimmy on rollout, it dissipated taxiing in. I though perhaps I’d hit and imperfection in the runway and didn’t give it a second thought.  There was no abnormality in the subsequent takeoff, but I encountered the same shimmy on landing back at home base.  Again once I slowed down it went away completely. The tire is fine and at 30 psi.  I can’t see anything obviously wrong with the gear. Sound familiar?

It's that bumpy runway at OSU.  They just resurfaced the runway at TZR.  You probably wouldn't have the shimmy if you were still based there.

[steingar]

34 minutes ago, mooniac15u said:

It's that bumpy runway at OSU.  They just resurfaced the runway at TZR.  You probably wouldn't have the shimmy if you were still based there.

Doubt it, since it happened at DLZ as well.  I don't recall much play at all in the rudder, so I might try a new tire for starters.  Still, a 1 AMU squawk isn't so bad.