GMC 1976 ZEO 6083 Maintenance Manual page 245

5- 2 6
BRAKES
sure the outlet ports are clean . Inspect the fluid reser-
voirs for foreign matter . Check the bypass and com-
pensating ports to the master cylinder bore to
determine if they are restricted .
5 . Remove the primary seal, primary seal protec-
tor and secondary seals from the secondary piston .
CLEANING AND INSPECTION
Use clean brake fluid to thoroughly clean all
reusable brake parts. Immerse in the cleaning fluid
and brush metal parts with hair brush to remove
foreign matter . Blow out all passages, orifices and
valve holes. Air dry and place cleaned parts on clean
paper or lint free clean cloth. If slight rust is found
inside either the front or rear half housing assem-
blies, polish clean with crocus cloth or fine emery
paper, washing clean afterwards .
CAUTION: Be sure to keep parts clean until
reassembly. Re-wash at re-assembly if there
is any occasion to doubt cleanliness-such
as parts dropped or left exposed for eight
hours or longer.
IF there is any suspicion of contamination or any
evidence of corrosion, completely flush the vehicle
hydraulic brake system . Failure to clean the hydrau-
lic brake system can result in early repetition of trou-
ble. Use of gasoline, kerosene, anti-freeze, alcohol or
any other cleaner, with even a trace of mineral oil,
will damage rubber parts.
Rubber Parts
Wipe fluid from the rubber parts and carefully
inspect each rubber part for cuts, nicks or other dam-
age. These parts are the key to the control of fluid or
air flow . If the unit is in for overhaul, or if there is
any question as to the serviceability of rubber parts,
REPLACE them! Inspect in accordance with the
following table. The table is organized by power
brake unit groups . Badly damaged items, or those
which would take extensive work or time to repair,
should be replaced . In case of doubt, install new
parts. Do not rely on the brake unit being overhauled
at an early or proper interval . New parts will provide
more satisfactory service, even if the brake unit is
allowed to go beyond the desired overhaul period .
MASTER CYLINDER INSPECTION CHART
Part Inspect For: Corrective Action :
Master cylinder body . Scratches, scores, pits,
Polish light damage smooth with
other damage affecting
crocus cloth ; replace piece, if
sealing or sliding action damage does not clean up quickly.
of piston seals in master
cylinder bore .
Damaged threads. Clean up or replace.
Cracks, structural damage . Replace.
By-pass and compensating Open and clean passage.
holes to be open .
Spring retainers. Check for cracks, de- Replace.
formation.
Master cylinder primary Nicks, scratches, cor- Do not repair ; replace.
and secondary pistons.
rosion on finished O.D .
surfaces .
Small holes in end open .
Clean.
Try fit in master cylinder Replace piston cylinder or both if
to be free with slight tight or sloppy .
play .
Master cylinder Hardness, holes, punch Replace.
reservoir diaphragm .
marks, cuts or abrasion .