d. At Brake Reline: Comprehensive Inspection of the power cluster and connections Some shops install new
piston cups or a repair kit to assure trouble-free operation during the life of the new lining.
An air cylinder leak, except at the inlet fitting, is due to a worn piston cup, a dent or corrosion in the cylinder shell, or a
piston loose on its rod
Internal pressure leak in the hydraulic cylinder, due to worn primary cup, pitted cylinder, or corrosion, is demonstrated by
creep of the stroke travel indicator during an extended holding application at low pressure.
Fluid leak at the rear of the hydraulic cylinder is due to cylinder pitting or a worn secondary cup.
Should hydraulic pressure build and fall to release (brakes "lock up") the hydraulic by-pass is blocked by dirt or corrosion,
or a swollen primary cup which extends over the port. A swollen cup indicates an improper or contaminated brake fluid.
Air in the hydraulic lines lengthens the stroke and must be bled from the system. At the cluster master cylinder, check for
Fluid level - low, below reservoir ports.
Filler cap vent - blocked, producing vacuum which sucks air past the piston secondary cup.
Secondary cup - worn, or pitted hydraulic cylinder.
Check valve - fails to retain residual pressure in system.
For servicing, it is more convenient to remove the cluster to a work bench. Remove filler cap and pour off brake fluid.
e. Air Cylinder Separate air cylinder from the cluster by removing fastening bolts. Separate cylinder shell from
head by taking out shell cap screws (8, 5/16-18 x 5/8 inch) and slide shell from head and piston. Piston cup and wiper can
be stopped from the piston. Piston, spring and boot can be pulled from head. Before assembling, lubricate the shell
interior and saturate the piston cup and felt wiper with a light engine oil. Install boot in piston groove. Align piston and
spring with head and compress them in order to snap boot into groove on head. Pass a small diameter drift through the
shell air inlet and use it to hold the spring compression while guiding the shell over the piston and head.
f. Hydraulic Cylinder After removing the air cylinder, pick lock ring from groove m end of hydraulic cylinder bore.
Internal parts should slide out or can be fished out. Do not overlook valve seat in end of bore Before assembling, lubricate
cylinder bore and parts with brake fluid. Be sure that lock ring is seated firmly in groove and that piston returns against th e
stop plate.
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