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Anybody have/had a main gear wobble at low speed?


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After landing and slowing to about human running speed my LongEZ has a nasty little wobble during braking only seems like it is one of the mains. If i release the brakes then it stops. It also seems worse if i have a passenger.


I watched the nose for shimmy thru the window and it is rock solid. Mine has the flox added as suggested in the CPs so i am not sure what it could be. Anyone have a suggestion?


Thank you

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Mine does it too on one side.  Discs are perfect.  Check your alignment. Mine is off on one side.  Best way to see which one is late in the day, when the sun is low, if you can see the shadow of your gear.  One will jiggle like crazy.  Hopefully only one!


What's funny is a lot RVs do it too and they never talk about it.......


Check with Dale Martin on the best way to align them.  His system is excellent.  Will get to mine soon......

Edited by flyingriki
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The main gear strut shimmy you refer to is generally caused by the disc not being perpendicular to the centerline of the main gear axle.  As Marc noted, a warped disc is the frequent culprit.


The shimmy is caused by uneven pulsating braking, even when consistent pedal pressure is applied.  The brake pads make intermittent contact with the pads, thus producing the pulsation.


If the caliper is stationary and the disc wobbles back and forth between the pads, brake friction will be intermittent.  Each time the brake "grabs", the wheel's axle is pulled slightly aft.  Since the brake pad is located at a moment away from the center of the main gear strut, the wheels are rapidly "steered" away from the desired toe-in position into a toe-out position.  As the wheel and disc continue rotation, the brake pressure reduces and the axles snap back to toe-in alignment.  That toe-out tends to spread the gear strut slightly and on a pulsating frequency.  The wheel/tires end up moving in and out as well as having a pulsating brake action.  A lot is going on in multiple directions and not much is good.


If this severe oscilating and pulsating action is allowed to continue for an extended period, it can cause damage to a landing gear mount that was not very robust to begin with.  Remember, most of the Long-EZs, VariEzes and Cozys are operated above the original design weights.  (See previous post on landing gear attachment upgrades).


It would seem that to avoid main gear vibration no run out can be allowed on the brake disc. However, there is frequently more to the situation than that.  I toured the Cleveland Wheel & Brake factory near Cleveland, OH some years ago and talked to one of the assembly inspectors about disc run out and that, what seemed, an excessive amount was frequently found on Cleveland parts.


I was amazed when he showed me the allowable runout spec.  I don't recall it now but I thought it was blacksmith wide at the time.  The inspector said the frequent problem for brake pulsation on flexible landing gear struts, like our glass one or the RV tubular ones, is not caused by just disc run out.  In fact some run out is expected during heating from high energy stops.  The culprit is sticky torque pins.  The calipers MUST be free to move around on the pins and follow the rotating brake disc as it wobbles back & forth applying consistent friction on the disc.


The reason the pins stick is they are dirty.  Even slight brake dust mixed with ANY wet lube (anti-seize, oil, grease, etc) will attract the dirt and make a sticky substance that slows or even blocks the caliper's abiity to move rapidly and freely on the pins.  That lack of caliper/pad freedom to move is what causes the pulsation and brake shudder.  The harder one brakes, the more severe the shudder becomes since the brake friction is higher.  In some cases the prake pads get broken in pieces also due to the tensile loads.


The fix is to be absolutely positive that the brake pins are perfectly free to move with the slightest pressure.  They should literally rattle when you cross the floor to ramp bump going in or out of the hangar. The torque pins and holes should be smooth, CLEAN and DRY, lubricated with a dry lubricant like Spray Silicone Lubricant.  Do NOT USE ANY GREASE OR OIL PRODUCTS.  Obviously one MUST not get any silicone lubricant on pads or disc.


Some folks insist on attaching solid metal brake lines to the Cleveland calipers.  That frequently reduces the ability of the caliper to move freely.


If you must connect the caliper directly to metal lines,  put a large loop in the small diameter line to allow movement or install a flex line between the metal supply line and the caliper.


Happy smooth stopping,


Terry Schubert

Central States Association

Newsletter Editor & Publisher

Long-EZ N9TS 4000+ hours



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