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Had a failure of the pitch trim servo motor during a low pass over my home airport last Saturday. At about 200 kts IAS and about halfway down the runway got a very noticeable (read that very noticeable) vibration in the control stick. Pulled power off and raised nose to gain altitude and lose speed until vibration stopped. Immediately realized that the pitch trim was not working. Made short approach and landed with no problem other than higher than normal stick force necessary to flare.
Upon inspection found the Mac 6A trim motor housing to be broken. The main trim shaft that works the trim tab had pushed the rear bearing plate out and scattered the gears inside the elevator. After thorough inspection of tab and elevator assembly I replaced the 6A motor with an 8A and test flew the plane. Everything works fine.
I don't believe the same kind of failure is possible with the 8A as the trim shaft passes through the rear plate instead of resting in it like the 6A. Don't know if this is a matter for the rest of you to consider but I can attest that the stick shake that resulted from the failure was quite a "heart starter" for me. I can take pics of the housing and parts if anyone needs to see the servo.
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