VG-21 Maintenance Item # 15 15 January, 1995
WHEEL SHIMMY: If you own a Varga, you have probably
experienced a nose wheel shimmy at some time. I think the most
The easiest way to look for nose gear steering wear and tear is to have someone hold the tail down while you turn the nose gear through it's travel and check to see if everything is tight. You can also try to move the nose wheel fore and aft and from side to side to see if the plastic bushings inside the strut are still in good condition. If anything moves in the wrong direction (up and down instead of fore and aft, for example) then you should take it off and examine it's attachment holes and fasteners for wear. Repair or replace any parts that need it. When you lubricate it and put it back together, it's probably better to have just a little friction than totally free movement.
Steering Yoke Inspection and Repair: The Steering Yoke is kind of a special case. I haven't seen one yet that didn't need to be shimmed a little. Making a shim isn't hard (I usually cut up a beer or pop can) but you must remove the lower strut to install it. This removal procedure is described in paragraph 6.4.1 of the maintenance manual. Worn shimmy dampener, torque link and steering arm attachment holes can usually be drilled oversize and bushed by you or your repair shop.
Inspection and Repair: The shimmy dampener was not made to be disassembled, but
I finally figured out how to replace the push rod "0" rings which are
Before removing the shimmy dampener assembly, check the rod end bearing, rod end bearing to yoke attachment bolt
and hole and the cylinder attachment bolt and hole for excessive play. If the Spherco TRE-4 rod end bearing is worn out,
get a new one. If the NAS 1297-4D-12 shoulder bolt is worn, get a new one. If the attachment hole on the shimmy
dampener is worn, it will probably have to be taken to a shop and bushed and reamed to the proper size.
Remove the shimmy dampener from aircraft.
Clean the dampener assembly thoroughly to remove all dirt, grease and hydraulic fluid.
Remove 12-24 x 1/4" filler screw (Don't lose this screw, they are hard to find!) from dampener. Inspect the fiber washer
for condition and replace if necessary.
Push the rod end bearing all the way in (as
close to dampener cylinder as it will go) and fill the cylinder
aircraft hydraulic fluid. A large syringe with a large needle works very well for this. Make sure all the air has been
removed. This may
require overfilling until all air bubbles stop
Reinstall the filler screw and tighten.
Wipe the dampener clean and dry of hydraulic fluid.
Move pushrod back and forth through it's full stroke while inspecting to see IF and WHERE hydraulic fluid is leaking out.
Pushrod movement will be jerky or noisy if there is still air in the dampener. If the dampener isn't jerky, noisy or leaking,
put it back on the airplane. If it is not leaking but is still noisy or jerky when you push the rod back and forth, refill it until
ALL the air is gone. When the pushrod action is smooth and quiet through it's full stroke put it back on the airplane.
If the dampener is leaking at the joint between one of the end caps and the cylinder casting, you will probably need to
take it to a shop and have the end cap pressed out so that the outer "0" ring can be replaced. Unfortunately, removal of
the end cap can sometimes score it and/or the cylinder wall so badly that it won't stay in under pressure when
reinstalled. You may have to repair or find or make new parts to fit if this happens. If you must remove an end cap,
make sure before you reinstall it that the pushrod hole is also in good condition and the proper inside diameter.
Worn Push Rod Seals: If oil is only leaking from around the pushrod holes, the following repair instructions to remove and replace the pushrod "0" ring seals may work for you.
Remove the oil filler screw and pump or drain out all the fluid.
Move the push rod until the rod end bearing end of the push rod is about 3 1/2" from the center of the filler hole. The
pushrod piston should be visible in the filler hole. Rotate the pushrod in either direction until the piston set screw is
visible and centered in the filler hole. Install an alien wrench in the set screw through the filler hole. Measure and write
down or remember the EXACT distance of the rod end bearing to the end of the shimmy dampener (dimension "A"). You
will need it for proper reassembly.
CAUTION! Before loosening the set screw make sure there are no burrs or sharp edges on the unthreaded end of the
pushrod. lf there are, carefully clean them off with fine emery cloth or a file or you will risk damaging the inside diameter
of the end caps or piston when you remove the pushrod.
Rotate the allen wrench counter clockwise and back the set screw out until it gently but firmly contacts the inside of the filler screw hole. This should hold the piston in place white you gently but firmly tap the unthreaded end of the pushrod out with a 5/16" diameter brass or aluminum rod. NOTE: You may wish to hold the alien wrench in the setscrew hole to help keep the piston from moving out of place while tapping on the pushrod.
After the pushrod has been removed you will be able to see the "O''rings by looking into the pushrod holes in the cylinder end caps. Using a sharp needle-like tool, carefully remove the "0" ring from its groove in the end cap. CAUTION: Be careful not to scratch the bore in the end cap or to push the "0" ring into the cylinder because it may be very hard to get out without removing an end cap.
After the "0" rings have been removed, inspect the end cap pushrod holes for wear or damage and repair as required.
Inspect and clean the "0" ring groove and carefully install a new "0" ring, again using CAUTION not to push the new "0" ring too far past the groove and into the cylinder.
Before reinstalling the pushrod, inspect the setscrew dimple and the ends for burrs and/or sharp edges. Remove them with a file or fine emery cloth as required. Any sharp edges left on the pushrod may cut the "0" rings when the pushrod is reinstalled and cause premature failure.
Lubricate the "0" rings with hydraulic fluid and reinstall the pushrod opposite of removal.
Fill the cylinder with hydraulic fluid, check for leaks and smooth operation and put the shimmy dampener back on the airplane.