500 
Oct 20/89  27-21-0 
Page 105 
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TROUBLE  PROBABLE CAUSE  ISOLATION PROCEDURE  REMEDY 
Insufficient trim knob travel or rudder trim travel (Cont) Rudder trim control system binding, trim knob forces excessive  Insufficient clearance between input rods or linkages and cranks or quadrants near full travel positions Cables on fwd cable drum or rudder trim actuator drum incorrectly wrapped Rudder trim actuator improperly installed or rigged Stops in rudder trim knob improperly installed Rudder trim actuator dry lube worn off Foreign objects interfering with system components and linkages Excessive cable tension  With rudder trim knob near full travel position, check for clearance between rods and cranks, etc. Fwd stops should be contacted before linkages run out of travel With rudder trim knob at full travel position, check if cable is completely unwrapped from fwd drum or rudder trim drum. Fwd stops in trim knob should be contacted before cable unwraps from drum Check system rigging per 27-21-0, Rudder and Rudder Trim Control System -Adjustment/Test Check if stops in trim knob are contacted before required travel is obtained Remove mounting bolt from upper end of trim actuator. Rotate trim actuator screw by hand and check for binding Check for foreign objects obstructing movement of system components and linkages Check cable tension. Refer to 27-21-0, Rudder and Rudder Trim Control System -Adjustment/Test  Remove interference Correct improper installation Adjust system as necessary Correct improper installation Apply lubricant MIL-L-23699 to screw and drum interior threadsRemove foreign objectsAdjust cable tension 

500 
27-21-0  May 15/81 
Page 106 
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TROUBLE  PROBABLE CAUSE  ISOLATION PROCEDURE  REMEDY 
Rudder trim control system binding, trim knob forces excessive (Cont)  Binding, worn or defective bearings in feel and centering unit Rubbing cables, misaligned or defective pulleys or fair-leads Binding, worn or defective parts in forward trim mechanism Binding, worn or defective parts in trim actuator Binding, worn or defective parts in torque tube Binding in power control unit valve input rods or power control units  Isolate feel and centering unit, examine pivot bearings. Refer to 27-21-82, Feel and Centering Unit -Removal/Installation Examine cable runs and pulleys Disconnect cables from trim mechanism drum and cycle mechanism with rudder trim control knob. Excessive force or binding indicates defective trim mechanism Remove mounting bolt from upper end of trim actuator screw by hand and check for binding Disconnect linkages connecting torque tube to rudder aft control quadrant, feel and centering unit, power control unit and standby actuator. Rotate torque tube to check for interference With rudder power control unit and standby actuator input rods disconnected from torque tube, cycle input rods by hand to check for binding input linkages  Replace worn or defective partsRepair or replace defective parts Replace or repair trim mechanism Replace defective trim actuator Repair or replace defective parts Replace defective power control unit 

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May 15/71  27-21-0 
Page 107 
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TROUBLE  PROBABLE CAUSE  ISOLATION PROCEDURE  REMEDY 
Rudder trim control system binding, trim knob forces excessive (Cont) Trim knob forces low Rudder centering faulty Excessive play in rudder surface Trim drifts from setting during flight  Rudder control system jammed or binding Excessive lubrication on rudder trim actuator Excessive system friction Defective centering unit Rudder system out of rig Worn or defective parts Excessive lubrication on rudder trim actuator  Check rudder pedals for excessive forces. If excessive forces are encountered, rudder control system is binding Check rudder trim actuator for excessive lubrication Check pedal breakout force. If it exceeds 18 lbs, system friction may be too high. Check for loose worn or defective parts. Check for rubbing or misaligned cables. Check for foreign objects interfering with system Check pedal breakout force. If it is less than 10 lbs, centering unit may be defective Check system rigging per 27-21-0, Rudder and Rudder Trim Control System -Adjustment/Test Check for worn or defective bearings or hinges in fin area Check rudder trim actuator for excessive lubrication  Refer to trouble item on binding or jammed rudder control system Cycle trim knob thru full travel until knob forces are normal Replace worn or defective parts. Remove foreign object Replace or repair defective centering unit Adjust as required Replace or repair defective part Cycle trim knob thru full travel until knob forces are normal 
　
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