Brake Assyembly

[Andreas Riedel]

During the last oel change the mechanic held the plane during run up with the parking brake and the brake assymble broke (exploded).
The damage looks to me that considerable force took place and I somehow can not believe that this can happen by purely applying the parking brake. I have attached some photos of the damaged part. I can not see any fault in the cast.
Thanks to the terific help and speed of Webco everything was sorted out.
Has anybody seen anything like this?
Your help would be greatly appreciated.
Andreas

[Zach Grant L1011jock]

Bent guides or pins. When they do not run in and out freely, when applied they over stress the casting, and youbget a fatigue type break exactly as you show. Notice the mounting plate and pin are dry and showing surface corrosion. They should be dry lubed and squeaky clean for proper performance of the brake system, and maximum service from the disks and linings.

Zach

[Andreas Riedel]

Thanks Zach, that explains it. Did not think that there would be so much force to bend the mounting braket. I will talk the shop and have them look at the other brake. Just in case we had changed the other mounting braket as well.
Thanks again
Andreas

[Kristin Winter]

Zach is correct. If that pin does not slide out when the brakes are applied hard, a bending force will be applied to the torque plate and the caliper where the pin mounts. While this may be a fatigue break, more likely it was a simple overload when extreme pressure was used to try to hold the brakes. Because the pins were not sliding freely, the brake pads would not be square on the disc, so the braking effectiveness is reduced. Because the breaking effectness is reduced, more pressure was likely applied to hold the aircraft during the full power run up. It was a vicious circle and something finally gave.

When I overhauled the landing gear in Maggie, I found one of the torque plates bend significantly and the other just a little. I replaced the torque plates, the spacers, the pins, the insulators, the pads, and the discs. Probably about time after 40 years and 4000 hours.

[Andreas Riedel]

Thanks Kristin, I will have the mechanic check for free movement of the pin on the other brake as well. I have felt a resistance on the pedal when applying the park brake since I have the plane. The brake would old the plane but the pedal does not move really when I apply the park brake.
In any case will have it checke.
Thank you for your help.
Andreas