Main Gear Shimmy on Tri Gear

[edclee]

I chased what I thought was a nose wheel shimmy for weeks, checking bearings, Changing tires, balancing tires, changing preload on the caster, rebalanced tires. Nothing worked. I landed at a nearby paved runway on a private strip to visit with the owner (I fly out of a grass strip, no problem on grass. And the shimmy was still there. Every landing starts after slowing to about 25 to 30 mph and continuing to maybe 10-12 mph. I mentioned the nosewheel shimmy to him and he said IT IS NOT YOUR NOSEGEAR, it is the left main! I took off and landed twice more while he stood beside the runway and it was definitely the left main. No wonder my nosewheel work had not affected the problem! Anyway, I jacked the plane and checked for play and there was a slight amount of twist in the gear leg. After checking everything, it was obvious that there was play in the cross bolt though the gear leg pocket in the fuselage. Everything about the structure was tight, nothing broken or loose, but there was play in the to maybe 10-12 mph. I mentioned the nosewheel shimmy to him and he said IT IS NOT YOUR NOSEGEAR, it is the left main! I took off and landed twice more while he stood beside the runway and it was definitely the left main. No wonder my nosewheel work had not affected the problem! Anyway, I jacked the plane and found there was play in the gear led pocket cross bolt-though. Removing the bolt with great difficulty showed some wear on the bolt so it had been "working" for some time. Ah HA, I thought, this must be it! So I drilled and taper-reamed an additional cross bolt and installed a tapered pin. This assures there is no possibility of slop any longer. Sure enough, there is no slop. A test flight showed the shimmy was still there, however. I tried balance, tire pressures, check alignment, changed tires, etc. STill there. In desperation, I removed the wheel pant and went landing. Shimmy is GONE. I had some old very light wheel pants and put one of those on the left side and went landing. Shimmy still gone. What the heck about a wheel pant mounted with the same bolts to the same place would make the heavier wheel pant shimmy? Any theories? The problem with the very light wheel pants is they are not very aerodynamically clean.