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FlyingFwyFreeman

Member
Where to Look? All of a sudden, my altitude hold function doesn't work. TRUTRACK Digiflight II. Track and Nav work. The display indicates ALT HOLD and + or - Verticle Speed, but the TRIM Indication is gone and it doesn't hold altitude. It's like the elevator servo just died. Does any of this sound familiar to anyone? Thanks for any guidance.
 
You may have a broken shear pin on the pitch servo. That’s relatively easy to fix. I recently had a similar situation with my aileron servo. In the hangar I could hear the servo operating, but there was no stick movement or resistance. The shear pin was indeed broken. Once replaced and recalibrated, everything was good again.
 
David Lewis said:
You may have a broken shear pin on the pitch servo. That’s relatively easy to fix. I recently had a similar situation with my aileron servo. In the hangar I could hear the servo operating, but there was no stick movement or resistance. The shear pin was indeed broken. Once replaced and recalibrated, everything was good again.
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Thanks, David, You wouldn't happen to know where and how to fix the shear pin? Guy
 
FlyingFwyFreeman said:
Thanks, David, You wouldn't happen to know where and how to fix the shear pin? Guy
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I don't mean to answer for David but the sheer pin is on the servo arm, the part that attaches to your control push/pull tube. With the A/P disengaged and on the ground, if you move your control stick you ought to feel a very slight resistance on the stick if the pin is in place but to really confirm this, you will need to go to the servo itself which is behind your baggage bulkhead.
Good luck.
 
Sorry for the delay. As Mehrdad said, the shear pin locks the servo arm to the stepper motor. It’s designed to break in high load situations. Not sure what servo you have but in my situation Dynon provided excellent instructions for replacement. Do a ‘servo shear pin’ search and you will learn how others addressed the issue. Be sure to observe your servo in operation to verify if the pin is actually broken. You might have another issue (lack of power or disconnected linkage) causing the problem. In my case, with the servo powered up the arm would still rotate freely. If this is true for your setup, it is an easy fix, but you’ll have to recalibrate the servo before using the system in flight. Let us know what you determine.
 
I had the shear screw break on my pitch servo a few years ago. You will need a new screw but will not have to remove the broken one. I don't think you could if you wanted to. There are several threaded holes just for this situation. Just use a new hole. I got the new screw from Midcontinent Avionics. It's pretty easy, except for going head first behind the rear seat in the 8.
 
Hi
Steve Watkins said:
I had the shear screw break on my pitch servo a few years ago. You will need a new screw but will not have to remove the broken one. I don't think you could if you wanted to. There are several threaded holes just for this situation. Just use a new hole. I got the new screw from Midcontinent Avionics. It's pretty easy, except for going head first behind the rear seat in the 8.
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Steve, Head first. Did you remove the servo to fix the shear pin? Guy
 
Not Steve . . . but to address my aileron servo repair I did not have to remove the servo. I’m pretty sure I would be able do the same with a pitch servo, but my installation is in a 7A. It really was a simple process. Access in a 4 or 8 might be more difficult.

Because a new hole (preexisting) is used, you will have to recalibrate your system before flight. And again, verify that the pin is actually broken. It may be that the servo has simply lost power or has somehow disconnected from the actuating linkage.
 
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