Steering horn replacement to remove shimmy

[BadMooneyRising]

I was working with my mechanic the other day to swap out the steering horn (newer style) on my 1974 F model. The plane has a very aggressive shimmy after landing when slowing down to about 20 kts, and will also shimmy if you taxi fast enough. So that's ultimately what we're trying to address.

After putting the plane on jacks and removing all the necessary bolts and linkages, we hit a deadend when we weren't able to remove the Shaft Assembly. We thought it would slide right out, but it seemed like it was getting held up somewhere. Does anyone know what we did wrong? Does the entire nose gear need to be dropped to perform a complete swap of the steering horn? 

 

 

[Marc_B]

@BadMooneyRising The nose wheel is sensitive to the fore-aft position.  Sometimes with new shock discs this pushes the nose wheel forward which makes it way more twitchy.  Check the plumb line and adjust either the collar or Mooney also has a thin spacer (washer) that you put at the top of the tack to compress the gear more and push the nose wheel further aft.

[Marc_B]

https://web.archive.org/web/20190207032823/http://donmaxwell.com/the-eight-second-ride-sb-m20-202/

Here is the Mooney SB. https://mooney.com/wp-content/uploads/2020/12/SBM20-202.pdf

[N201MKTurbo]

I believe if you retract the gear, the steering horn can be dropped off its pivot. A picture would help.

[Ragsf15e]

28 minutes ago, N201MKTurbo said:

I believe if you retract the gear, the steering horn can be dropped off its pivot. A picture would help.

I want to say my mechanic retracted it halfway to work on the nose gear.  Either that or he was punishing me for doing something stupid as he disconnected the gear from the motor and then had me holding the mains up about halfway and then said don’t move.  I swear he went for coffee.  Fully retracted is probably easier…

[Utah20Gflyer]

In my case I removed the lower cowling to get better access to the steering horn.  With the lower cowling in place it is really tight.  Not sure which way you are trying it.  

[AJ88V]

Recommend you check your tire pressure before doing anything else.  Mine definitely shimmies worse when the tire pressure is low.  

Not meaning to start an argument, but typically keep my nose gear tire more like 35 psi than 30.

[Ragsf15e]

5 minutes ago, AJ88V said:

Recommend you check your tire pressure before doing anything else.  Mine definitely shimmies worse when the tire pressure is low.  

Not meaning to start an argument, but typically keep my nose gear tire more like 35 psi than 30.

I want to say my poh shows like 49psi for the nose? 30 for mains?

[65MooneyPilot]

Mooney models: C,D,E are 30 PSI All wheels. F models 30 psi mains 49 psi nose wheel. These are pre 1966 Mooneys. As always check the manual for your Mooney.

[AJ88V]

11 hours ago, 65MooneyPilot said:

Mooney models: C,D,E are 30 PSI All wheels. F models 30 psi mains 49 psi nose wheel. These are pre 1966 Mooneys. As always check the manual for your Mooney.

Yep, good advice to CHECK THE POH. (Didn’t realize the F was that high!)

That said, my nose wheel def shimmies when the tire pressure is low, so worth double checking that if yours is shimmying.

[65MooneyPilot]

I personally don’t get wrapped around the axle about the tire pressure unless it is below the book value. I personally put in a few extra psi because tire pressures change with outside air temp. Using nitrogen is way better but I am not. 
As far as nose wheel shimmy’s go a lot of owners suspect loose steering for a shimmy problem. In my case my nose wheel gear was severely worn out. I jacked up the plane and I could move the whole nose gear vertically a half inch. I took it off and sent it in to LASAR and they sent me an upgraded rebuilt one. After installing it, it was like having a new plane. Super smooth taxiing, taking off or landing. 

  

[M20E for me]

I had never felt a nose gear shimmy until last Friday.  After landing and exiting the runway I receive taxi instructions right after hearing the ground controller give clearance to someone else to taxi the opposite direction towards me from the other end of the taxi way.  This is normal procedure and they will tell each plane to taxi on the right side of the taxi way.  I normally taxi between 15-20mph when the controller asked me to expedite my taxi.  I obliged and got up to about 35mph and after about 15 seconds something set off the nose gear and it started a violent shimmy.  I’ve had the 65 M20E for 3 years now and had never felt the slightest shimmy.  Stepping on the brakes and slowing down made it go a way but it took a few seconds.  Something to keep my eye on.

[cliffy]

Tire pressure and steering linkage in the top of the nose wheel well. 

Lift the nose wheel off the ground and see how much loose left/right steering play you have 

If more than a few degrees check the gaggle of linkage parts up in the top of the wheel well 

to see which ones are worn. LASAR sells the parts and shims. 

Axle position for caster plays a part also in the diagnosis. Drop a line as shown in the SB. 

The main vertical bolt that the gear rotates around has a bushing that can be reamed for a larger bolt if loose

That bolt has a torque value that needs to be checked each annual along with greasing it 

the torque value was lowered by Mooney in later years by SB, Torque to the newer SB each annual.