Important Tru Trak Service Bulletin

[Roger Lee]

Hi All,

 

Here is a Tru Trak service bulletin. It affects a large number of the Tru Trak auto pilots in CT's. On the pitch servo you need a little screw retainer bracket which can be retro fitted at you hanger, but on the roll servo in the baggage compartment you will need to send the servo to Tru Trak for the mod. To request the screw retainer bracket and get an RMA number for the roll servo you will need to register on the Tru Trak website and do a request.

I may give them a call and see if they will send me a roll servo so I can just swap them out at my shop and not have to make a customer wait a week or two for shipping, but i don't know if they will do that? I will let you know, but you may be on your own for this.

Servo Service Bulletin 060810.pdf

[Runtoeat]

Oh man, just when I thought I was getting ahead of the game after my stabilator mod and Garmin radio SB, Roger comes up with ANOTHER SB!:blink: Actually, another good "heads up" from you Roger. I called TruTrak today and, as usual, they were friendly and helpful. John said to get the S/N off of the roll servo and call back to them. He said the screw retention bracket for the pitch servo would be sent when I call back and I would be given the RMA for sending in the roll servo for factory modification.

[airhound]

June 10

[Runtoeat]

I got my roll servo back from TT. In place of the previous screw that held the fiber wheel on the shaft, It now has a new shaft with a lock nut. My A&P is wondering how much torque is supposed to be used for the nut? The only way to hold the shaft while applying torque is to hold the fiber wheel. Don't really want to use channel lock pliers on this wheel. Just snug the nut down and apply a dab of torque check paint?

[airhound]

Say Runtoeat, was the turn around 26 Oct-15 Nov or there abouts?? three weeks?

[Runtoeat]

Say Runtoeat, was the turn around 26 Oct-15 Nov or there abouts?? three weeks?

 

The actual turn around time with Trutrak was about 8 days. Same with my friend who also sent his servo in. My modified servo has been sitting on the bench and will be installed this week and the screw retainer will be installed on the pitch servo too.

[TrutrakTech]

I got my roll servo back from TT. In place of the previous screw that held the fiber wheel on the shaft, It now has a new shaft with a lock nut. My A&P is wondering how much torque is supposed to be used for the nut? The only way to hold the shaft while applying torque is to hold the fiber wheel. Don't really want to use channel lock pliers on this wheel. Just snug the nut down and apply a dab of torque check paint?

 

This particular reason is why we install the torque enhancers now instead of allowing them to be left off. We've had a few customers break the brass shear screw while trying to cinch down the nut. That said, you don't have to get crazy with the tightening. In our exhaustive tests of that setup versus the old screw setup, the required dynamic torque to keep the screw backing off remained constant all the way off and was very close to the static torque. I do not remember the exact numbers though. :blush:

[Tom Baker]

This particular reason is why we install the torque enhancers now instead of allowing them to be left off. We've had a few customers break the brass shear screw while trying to cinch down the nut. That said, you don't have to get crazy with the tightening. In our exhaustive tests of that setup versus the old screw setup, the required dynamic torque to keep the screw backing off remained constant all the way off and was very close to the static torque. I do not remember the exact numbers though. :blush:

 

The only problem Is the torque enhancer will not fit through the hole in the mounting bracket.

[TrutrakTech]

The only problem Is the torque enhancer will not fit through the hole in the mounting bracket.

 

True with the CT, unfortunately. But there are several other applications where the bracket has clearance for installing the entire assembly.

[Jim Meade]

From the SB, word for word:

"Recent reports have suggested that there could be a problem with the new integrated thread-locker servo arm screws that have been sent out for retrofit by customers in the field."

Apparently some users had reason to retrofit the servo arm screw and the new screw - the retrofit screw - would not stay tight in some cases.

"Reports indicate that the screw could back out of its hole in the end of the servo shaft during normal usage."  This is the new screw.

"In speaking with the manufacturer of the new servo arm screws, the suspected cause is residual chemical thread-locker in the threads of the servo shaft which was the previous method for locking the arm screws in place."

The old screw used thread locker such as loctite and when the old screw was removed and the new (retrofit) screw installed the residual thread locker didn't always permit a tight fit so that the new screw could work out.

"While there are only a very few reports of this actually happening, Trutrak Flight Systems wants to take steps against the possibility of this happening. We will include the bracket shown below with all new servos shipped with the current servo arm screw. This bracket will also be available to all customers with the current servo arm screw configuration as a field retrofit solution."

TruTrak changed to a shaft with threads that used a nut to hold the arm or capstan, but for those servos with the existing screw hole the bracket was offered to insure the residual thread locker in the screw hole didn't prevent the new screw from securing the arm.

Mid-Continent says they have no parts or procedures for changing the capstan servo.  They have brackets for the arm servos.

My take on this is that one inspect the servo periodically and make sure the screw is not backing out.  Maybe some witness paint is advisable so any rotation is easy to see.  If the screw doesn't move, this is a case of nothing is broke so don't fix it.  If you have reason to take that screw out then you are well advised to go to MCICO and get the bracket arm and install it per the SB.