Nose Wheel Shimmy

Nose Wheel Shimmy

Can you give me some ideas that can correct nose wheel shimmy. I have 1968 172i that has developed a shimmy upon landing. Any ideas that I could look into - to fix this problem.
Thanks,
Mike Woodson

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Re: Nose Wheel Shimmy

The purpose of the nose gear is to keep the prop from hitting the ground when you park the aircraft.

That said, rebuilding the shimmy damper and balancing the nose wheel and tire should solve your problem.

Afterward, re-read line one.

Otto Croy
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Re: Nose Wheel Shimmy

My nose wheel shimmys as of late and the shimmy occurs at the end of my landing roll - when I am going slow. I get no shimmy throughout takeoff and rotation.

Because of this last fact I do not believe it's a front end problem e.g. balancing of the wheel, that sets up the vibration.  I think the cause could be in the rear wheels/ arrangement.  Unequal tire pressures, dragging brake pads due to a caliper that is sticking, potentially some kind of miss alignment or like they said in My Cousin Vinny, "mud in the tires" (picked up if its been on a grass strip or parked in the grass). 

The major difference between take off and landing is an angry engine that is producing a lopsided torque on the rear wheels.  I believe this torque with no braking is major difference in the behavior of the plane.  Next time you land with the front wheel still off the ground, notice if the mains are vibrating.  When you slow down and the full weight of the engine is put on the front wheel it now has to deal with the vibration caused by the mains and it can not cope with the amount of vibration.  I wouldn't think a repair of the dampers will help if the excitation caused by the mains is outside the design capability of the shimmy dampers.

just a thought, I'd be interested if anyone else has some comment on this.

Barry Schneidman
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Re: Nose Wheel Shimmy

I recently rebuilt my shimmy damper on the last annual.  It looked like it had never been touched before and I assumed it had no oil in it.  It would shimmy on landing roll out if I did not maintain enough back pressure on the yoke. 

Upon disassembly I found it was servicable and probably did not need rebuilding.  The paint was stripped and it was repainted.  A new seal kit installed and it was put back on the plane.  Upon flight testing is had the same amount of shimmy as before.  It looked a lot better though.

I would think that the shimmy would be related to the geometry of the nose wheel strut (caster angle etc.) and any wear or play in bushings and pins or bolts.  Regardless a rebuilt damper did not change things.

The shimmy is manageable and I can accept it as normal.  If good landing practices are used there is no problem.  I always treat the nosewheel as tender and land will full or near full up elevator.  Especially with no one in the back seat. 

The plane is a 172K with under 1700 hours TT.

Ron

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Re: Nose Wheel Shimmy

I too had occasional shimmy on my 172.  A friend of mine told me about a shimmy dampener made by Lord. I purchased one from Aircraft Spruce a year ago and it has never shimmied again.  It needs no oil or maintainence. Well worth the money. Lord garuantees it not to shimmy.

Rich

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Re: Nose Wheel Shimmy

I have a 2000 model 172 and replaced the shimmy damper with a Lord damper. it made a huge difference in taxi, takeoff & roll out. I highly endorse this product. NO more shimmy at any speed.

Jimmy Westray
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Re: Nose Wheel Shimmy

I also get nosewheel shimmy on occassion when landing at high speed. I once rebuilt the shimmy dampener. It helped, but did not remove the problem. I too now accept it as a "standard" characteristic, but can pretty much control it by careful landing control and tire pressure. In fact, if I don't have the the proper nosewheel pressure, I can guarantee I will get shimmy.

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Re: Nose Wheel Shimmy

The most often cause of the dreaded nose wheel shimmy is the lack of steering collar shimming. I have addressed numerous squawks in my shop that the dampener was just overhauled and it still shimmy's. The nose gear assembly must be removed from the airplane to accomplish this. Two other things that come to mind are the strut pressure and the tire pressure.
-Tom

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Re: Nose Wheel Shimmy

MY MECHANIC REPAIRED/REBUILT THE NOSE WHEEL DAMPER A
NUMBER OF TIMES WITH LIMITED SUCCESS.  I REPLACED THE DAMPER WITH A 'LORD' UNIT OVER THREE YEARS AGO AND HAVE NEVER EXPERIENCED NOSE WHEEL SHIMMY SINCE.  I UNDERSTAND THAT CESSNA IS USING THE LORD DAMPER ON ALL NEW AIRCRAFT.

Stanley Ashman
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Re: Nose Wheel Shimmy

The nose shimmy is almost always the steering collar shims and / or the torque links having too much slop.  When you replace the steering collar shims there is a washer that looks like a shim, only thicker.  Replace that when you add shims.  The lord shimmy dampener works very well, but even with that you can have shimmy if the collar and torque links are not tight.  We see service life of approx. 600hrs between shimmy events when the collar is re-shimmed and torque links fixed.

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Re: Nose Wheel Shimmy

I agree with Tom,  Cessna nose gears are very sensative to anything being loose or worn.  The steering collar is so often overlooked and really not that hard to fix.

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Re: Nose Wheel Shimmy

I had been having a sometimes vicious shimmy on roll-out, that we could not shim out of the scissor link.  At annual I replaced all the bushing and bolts, about $150 worth, and it has been worth EVERY penny I paid.

My A&P said to grab the scissor link from the back and if it could wiggle it was worn out.  We had rebuilt the dampener 4 months ago, so it was doing as well as it could.

Rod

--
Rod Richeson
PP ASEL since Mar 17, 2007
PP ASEL IA since September 27, 2007
1969 Cessna 172K

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Re: Nose Wheel Shimmy

Anyone know the pressure to place in a front strut for a 172 cessna

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Re: Nose Wheel Shimmy

Hi Lorne;

My 1978 C-172 is 45 psi.  If I don't have an air source with a gauge, I usually raise the nose off of the ground, inflate it, and then set it back on the ground and compress the strut a few times.  If it sits with more that about 3 inches of chrome showing on the strut, I release a little air until it sits at about 3 inches.  This seems to be a good approximation.  Hope this helps.

Jon

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Re: Nose Wheel Shimmy

Anything loose in the nose strut can cause a shimmy.  The damper is only designed to reduce the small amount of normal vibration, not counteract a large shimmy.  The collar is a prime suspect, and of course an out of balance tire can cause it too.  I can recommend a mechanic who is an expert at fixing 172 nose wheel shimmy problems in Roanoke, VA if you are near there (Charlie at Roanoke Aero SErvices).

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Re: Nose Wheel Shimmy

Ditto on the steering collar and the torque links. If you grab the torque link assy and feel ANY looseness you are going to get nose wheel shimmy. Replace the bushings in the torque links and also install the shims per the maintenance manual and you will find that your shimmy magically disappears.

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Re: Nose Wheel Shimmy

I have had the shimmy problem in the past.The last fix was to replace the front tire.That has fixed the problem ,,,,so far.
The shimmy damper was rebuilt,refilled,and tightened up on it's mounts,all without lasting success.The nose gear has always been tight so that was never a problem.

My shimmy would come if you carried too much speed when the nose gear touched down.It never shimmied on take-off.
My A&P said this was because the nose wheel is lightly loaded (at first) on touchdown,that gives the wheel a chance to start an occilation that would carry through the landing until the A/C was almost stopped.The fix was to get a new tire and balance the assy.

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Re: Nose Wheel Shimmy

After complaining for years about nose wheel shimmy and having my A&E overhaul it at each annual, I installed a Lord mount.  It solved the problem and the (172XP) has been shimmy-free for ten years.

I understand that Cessna is installing the Lord mount on all new 172's.

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Re: Nose Wheel Shimmy

Hello,
I would like to know if Lord makes a shimmy dampener for a 1979 182 RG.

The research that I have conducted to date seems to indicate that they curently do not offer a shimmy dampner for the retractable gear 182's.

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Re: Nose Wheel Shimmy

In the case of shimmy at the lower speeds, it is an effect of spatial rigidity and as such just like a gyro spining down with a tendency to tumble. An imbalance of the nose wheel will aggravate the feel of the shimmy simply because its frequency is less. All that was said to recommend that you check the shimmy damper service and the balance of the wheel.

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Re: Nose Wheel Shimmy

I am an A&P IA and just questioning what some of you are referring to as torque links.

By torque links do you mean the "scissors"?

How bout mis adjustment and connection of the steering rods as well as the collar and all attachments as well as tire balance and replacement due to wear caused by shimmy.

Most of the time I see mechanics just re attaching the steering rods without checking the rigging properly.

And shimmy dampers are not overhauled.  All you can do is clean them up inside and replace the seals.  Anything else is a matter of part replacement.

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Re: Nose Wheel Shimmy

I found a shimmey dampener on www.aec-inc.com for $795 which was a lot cheaper than Lords.

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Re: Nose Wheel Shimmy

I like to know different ways things are done,Do you have a easy way to remove torque link bushings. Thanks

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Re: Nose Wheel Shimmy

ron christen Wrote:
-------------------------------------------------------
> I like to know different ways things are done,Do
> you have a easy way to remove torque link
> bushings. Thanks


Basically you don't remove them, you drill them out.  First use a drill bit (.375 I think) to align the link on a drill press.  Use a machine vice and blocks, clamps etc to hold the link in place straight.  Gradually increase the size of the drill bit removing a small amount of material each time.  Don't go all the way through both bushings, just do one at a time flip the link over to do the other one.  Don't try to drill out the whole thing, once the bushing is thin enough you can use a punch to collapse the remainder of the bushing inward and then extract with no damage of any kind to the link.

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Re: Nose Wheel Shimmy

Thanks scott The same way I do them I  thought maybe someone had made a tool to remove bushings for starter bushings,torque links etc.  I myself have sometimes made a tool to repair things,  crude but works well Thanks again Ron

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