I have over 1000 hours on my 6A with never experiencing any main gear shimmy. Then last April I did a perfect greaser landing and held the nose up until it fell at about 40 kts and all of a sudden I got a violent left main gear shimmy. Only change I had done recently was increased tire pressure from my normal 32-35 psi to 38 psi. I have no gear leg stiffeners and always statically balanced my wheel assembly. I disassembled all the gear and brake parts to try and determine the cause. Nothing obvious. I took the opportunity to do Vans SB-00047 that replaced fluid with 83282 and updated to the high temp o-rings. I also rebuilt one of the master cylinders. Put it all back together and had no more shimmy. I did not rebalance the wheels as when I put on the tires 100 hours prior they did not require any weights to balance.
Fast forward to a few weeks ago, and 60 hours (~50 landings) of shimmy free flying, and all of a sudden I got some violent shimmy again. I had just finished my condition inspection and had put on new brake pads. I had not checked tire balance as again, I had been flying for several years with no change to tire, tube, or wheel (except tire pressure back to 32-35 psi) so assumed still balanced. I jacked up the plane, spun the wheels, and noticed the new brake pads were dragging so, per reading some threads here on VAF, I added a 0.025” shim to the caliper assuming somehow the brake dragging was causing the shimmy. Went for a flight and shimmy solved. Flew a couple more flights and no shimmy. Then a couple days ago, after doing a landing to full stop, I took off again and after a short flight landed and had some moderate shimmy. Shimmy only happens at landing and when slowed to 40 kts with or without application of brakes. Shimmy only stops when slowed to 10 kts. No shimmy when taxiing at any speeds I tried up to 25 kts.
Ok, back to wheels off and brakes checked. I decided to check the tire balance. Well, it turns out wheels were way out of balance and I would need to add about 6 oz at the stem to get the left side to balance. Weird. So I decided to spin the tire 180 degrees on the wheel and try balancing again. That showed I need 5 oz at 180 degrees from the valve to balance. So it seems somehow my tire has gotten way out of balance. Tire still has lots of tread on it after 3 years and ~150 landings. No flat spots, it runs true and round.
So I believe I need new tires as I think anything over 2 oz to balance is excessive. My question to the crowd (for those still reading): what would make a tire change balance so significantly? I am not assuming my earlier shimmy had the same cause as my current shimmy. Maybe the first shimmy several months ago was caused by tire pressure or something else and somehow unbalanced the tire causing the current shimmy. Do you agree the next thing I do is get new tires?
Fast forward to a few weeks ago, and 60 hours (~50 landings) of shimmy free flying, and all of a sudden I got some violent shimmy again. I had just finished my condition inspection and had put on new brake pads. I had not checked tire balance as again, I had been flying for several years with no change to tire, tube, or wheel (except tire pressure back to 32-35 psi) so assumed still balanced. I jacked up the plane, spun the wheels, and noticed the new brake pads were dragging so, per reading some threads here on VAF, I added a 0.025” shim to the caliper assuming somehow the brake dragging was causing the shimmy. Went for a flight and shimmy solved. Flew a couple more flights and no shimmy. Then a couple days ago, after doing a landing to full stop, I took off again and after a short flight landed and had some moderate shimmy. Shimmy only happens at landing and when slowed to 40 kts with or without application of brakes. Shimmy only stops when slowed to 10 kts. No shimmy when taxiing at any speeds I tried up to 25 kts.
Ok, back to wheels off and brakes checked. I decided to check the tire balance. Well, it turns out wheels were way out of balance and I would need to add about 6 oz at the stem to get the left side to balance. Weird. So I decided to spin the tire 180 degrees on the wheel and try balancing again. That showed I need 5 oz at 180 degrees from the valve to balance. So it seems somehow my tire has gotten way out of balance. Tire still has lots of tread on it after 3 years and ~150 landings. No flat spots, it runs true and round.
So I believe I need new tires as I think anything over 2 oz to balance is excessive. My question to the crowd (for those still reading): what would make a tire change balance so significantly? I am not assuming my earlier shimmy had the same cause as my current shimmy. Maybe the first shimmy several months ago was caused by tire pressure or something else and somehow unbalanced the tire causing the current shimmy. Do you agree the next thing I do is get new tires?
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