Brake System Cessna 172



                             BRAKE SYSTEM -MAINTENANCE PRACTICES
             1. Description and Operation
A. The hydraulic brake system is comprised of two master cylinders, located immediately forward of the pilot’s rudder pedals, brake lines and hoses, and single-disc, floating cylinder brake assemblies located at each main landing gear wheel.
B. The parking brake system is comprised of a pull-type handle and mechanical connections which are linked to the rudder pedal assembly. Pulling aft on the brake handle applies mechanical pressure to the rudder pedals, activating the brakes and locks the handle in place. Turning the handle 90 degrees will release the parking brake and allow for normal operation through the rudder pedals.
C. Brake operation is accomplished by pushing on the upper part of each rudder pedal. This motion is mechanically transmitted to the respective brake master cylinder, and through fluid-carrying lines out to the brake assembly where fluid pressure acts to exert friction (through brake pads) against brake discs. 
        2. Brake Line Removal
A. Brake lines in the system are mostly metal, with flexible rubber lines installed near the master cylinders. Rigid lines may be replaced in sections using pre-formed parts available from Cessna. Flexible lines should be inspected for cracks, deterioration wear and damage, and are also available in replacement assemblies through Cessna.
        3. Brake Assembly and Line Removal/Installation
A. Remove Brake Assembly
(1) Ensure parking brake is OFF.
(2) Disconnect brake line at brake assembly.
(3) Remove bolts securing back plate and remove brake assembly.
NOTE: If torque plate needs to be removed, wheel must be removed from axle. If brake disc is to be removed, the tire and wheel assembly must be removed, deflated and split.
(4) Inspect components. Refer to Brake Component Inspection below.
B. Install Brake Assembly
(1) Position brake assembly in place and secure using bolts. Torque from 80 to 90 in-lbs 
(2) Reconnect brake line and bleed brakes.
C. Remove Brake Lining
(1) Remove back plate.
(2) Pull brake cylinder out of torque plate and slide pressure plate off anchor bolts.
(3) Place back plate on a table with lining side down flat. Center a 9/64-inch (3.58 mm) punch in the roller rivet, and hit the punch sharply with a hammer. Punch out all rivets securing the linings to the back plate and pressure plate in the same manner.
D. Install Brake Lining
(1) Install new lining on back and pressure plates. Secure to plates using rivets.
(2) Position pressure plate on anchor bolts and place cylinder in position so that anchor bolts slide into the torque plate.
(3) Install back plates with bolts and washers. Torque the nuts to 100 to 140 in-lbs
       4. Brake Component Inspection
A. Brake components should be inspected as follows:
(1) Clean all parts except brake linings and O-rings in dry cleaning solvent and dry thoroughly.
(2) Install all new O-rings. Ensure all components are clean and lubricated with brake fluid before reinstallation.
(3) Check brake linings for deterioration and wear. Minimum allowable thickness is 3/32-inch 
(4) Inspect brake cylinder bore for scoring. A scored cylinder will leak or cause rapid O-ring wear. Install a new brake cylinder if the bore is scored.
(5) If the anchor bolts on the brake assembly are nicked or gouged, they must be sanded smooth to prevent binding with the pressure plate or torque plate. When new anchor bolts are installed, press out old bolts and install new bolts with a soft mallet.
(6) Inspect wheel brake disc for thickness. Minimum thickness is 0.205 inch (5.207 mm).

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