Fixing nosewheel shimmy + upcoming annual

[AlexLev]

I have an upcoming annual inspection next month and a decently bad nosewheel shimmy on landing (rudder pedals violently engage). I wanted to get a head start on looking for parts + planning.

Reg shimmy: Taking all pressure off nosewheel can sometimes help it it a bit, or hitting the rudder pedals a bit back and forth myself can help. No controllability issue, but would like to get it fixed this annual. The nosewheel truss was rebuilt by LASAR in 2011 -- it looks to be in decent shape, but it does have some left and right play while up on jacks.

Should this be overhauled/replaced potentially? My shock discs are also old, perhaps original - but look good and pass the test in the service manual still. Replacing them is sort of expensive and a PITA, so I keep deferring it until it fails the test (and they seem to hold on)..

Any thoughts on priorities for this annual if this was your plane?

1) vacuum pump is pretty old with lots of hours, a Rapco unit but seems to be functioning fine.

2) battery is also from 2013 or 14 but also seems to be doing ok.

3) as mentioned; shock discs + nosewheel shimmy - not sure how to address yet.

misc stuff like carb temp probe prob needs replacing, etc.

Any guidance would be appreciated!

-Alex

[McMooney]

2 hours ago, AlexLev said:

I have an upcoming annual inspection next month and a decently bad nosewheel shimmy on landing (rudder pedals violently engage). I wanted to get a head start on looking for parts + planning.

Reg shimmy: Taking all pressure off nosewheel can sometimes help it it a bit, or hitting the rudder pedals a bit back and forth myself can help. No controllability issue, but would like to get it fixed this annual. The nosewheel truss was rebuilt by LASAR in 2011 -- it looks to be in decent shape, but it does have some left and right play while up on jacks.

Should this be overhauled/replaced potentially? My shock discs are also old, perhaps original - but look good and pass the test in the service manual still. Replacing them is sort of expensive and a PITA, so I keep deferring it until it fails the test (and they seem to hold on)..

Any thoughts on priorities for this annual if this was your plane?

1) vacuum pump is pretty old with lots of hours, a Rapco unit but seems to be functioning fine.

2) battery is also from 2013 or 14 but also seems to be doing ok.

3) as mentioned; shock discs + nosewheel shimmy - not sure how to address yet.

misc stuff like carb temp probe prob needs replacing, etc.

Any guidance would be appreciated!

-Alex

Replacing the tire and shimming the nose gear fixed my shimmy.

Really think it was mostly replacing the nosewheel tire that did it

Edited November 16, 2020 by McMooney

[Rwsavory]

McMooney beat me to it. How old is your nose wheel tire?  We had a shimmy, and a new tire solved the problem.

[DXB]

1) Assuming it drives your primary AI, vac pump failure in IMC sucks.  Wouldn't delay if over 600hrs on a standard dry vac pump.  

2) You could do a formal battery capacity test to decide, which is a bit of a pain and I've found A&Ps have little interest in doing it.  The cheap automotive load testers that measure CCA will identify a really bad battery but may miss ones that are marginal and merit replacement.  I'd be biased toward replacement in your case. 7 years is near end of useful life for even most Concorde batteries I think, and the strength of you battery could easily determine what kind of day you'll have after an alternator failure.  It's ~O.35amu for a Concorde RG53A, and it's a quick and easy swap to do yourself.  

3) Let me know what you find - I'm starting to have the same issue.  Did it have the beefier LASAR steering horn also done at the same time?  In my case making sure the nose wheel is a bit hyperinflated on the ground seems to prevent - I got it recently got it after a flight that climbed into cold air, so I think reduced tire pressure on landing was a contributing factor.  I did change the nose tire last year also before the tread was fully gone for the same reason, but underinflation can still certainly cause it in my case.  

BTW: good thread on A-h load testing vs. measuring CCA

 

[Immelman]

I suggest getting your nosewheel off the ground, get your head up there and start wiggling things, looking closely for where the play is? If the truss was rebuilt, that is a major component. How about the steering horn? How about the little tiny bearing (going from memory here) That the steering horn attaches to (there's a small one very high and forward). Really everything between the pedals and the tire should be looked at for undesired play.

 

 

[rbridges]

2 minutes ago, Immelman said:

I suggest getting your nosewheel off the ground, get your head up there and start wiggling things, looking closely for where the play is? If the truss was rebuilt, that is a major component. How about the steering horn? How about the little tiny bearing (going from memory here) That the steering horn attaches to (there's a small one very high and forward). Really everything between the pedals and the tire should be looked at for undesired play.

 

 

mine was the steering horn.  Replacing it got rid of the shimmy.  I could also tell my rudder had less play in it during preflight.

[carusoam]

Look up the eight second ride on DMax’s site...

It details what shimmy from the worn steering horn and other bits can be like...

Getting the nose gear OH’d is a Lasar specialty...

Compare what you feel, to these details... 

As far as donuts go... check their age, stamped on the side... see if they are ancient.... there is a compression test in the MM to define if they need to be replaced...

Best regards,

-a-