Master Cylinders; Composite Master Cylinder; Cast Iron Master Cylinder - Chevrolet 1988 Light Duty Truck Repair Manual

5-4 BRAKES

COMPOSITE MASTER CYLINDER

The Delco-M oraine Com posite Master C ylinder has
identifying inform ation stam ped into the front outlet tube.
The first and second digits are the build code. The third
digit indicates the year it was built (a 5 means 1985 or a
means 1987). The last digits indicate the day it was built
(271 m eans it was the 271st day of the production year).
NOTICE: Do n o t h one th e m a s te r c y lin d e r bore.
W hen the brake m a ste r c y lin d e r is overha ule d ,
it is re c o m m e n d e d th a t th e c y lin d e r b o d y be
re p la c e d ra th e r than " cle a n e d u p " by h o n in g
th e bore. The m a ste r c y lin d e r has a hard, h ig h ly
p o lis h e d " b e a r in g iz e d "
p ro d u c e d by d ia m o n d b o rin g fo llo w e d b y b a ll o r
ro lle r b u rn is h in g u n d e r heavy pressure . H o n in g
w ill d e s tro y th is s u rfa ce w h ic h w ill cause ra p id
w ear o f ru b b e r cu p s.
NOTICE: Do n o t use ke ro se ne , gaso lin e , o r any
o th e r u n a p p ro v e d s o lv e n ts fo r c le a n in g o r
flu s h in g m aste r c y lin d e r a nd c o m p o n e n ts . The
use o f these as s o lv e n ts o r any o th e r w ith a
trace o f m in e ra l o il w ill dam age ru b b e r parts.
+-► R em ove or D is c o n n e c t (F ig u res 9 and 10)
1. Cover (1).
2. Diaphragm (2).
• Drain all the brake fluid from the reservoir.
3. Reservoir (3) and grom m ets (4) (figure 11).
• Clamp the m ounting flange of the cylinder in a
vise and pry the reservoir off with a bar.
4. Snap ring ( 1 1 ).
5. Primary piston assem bly (12).
CAUTION: In the following step if air pressure is
used to remove the secondary piston, place the
open end of the cylinder bore approxim ately 25
mm (1-inch) from a padded workbench or other
surface to catch the piston when it comes out
of th e b o re. A p p ly low a ir p res su re very
carefully to ease the piston out of the bore.
Never point the open end of the bore at anyone
when applying air pressure. The piston may
come out of the bore with considerable force
and cause personal injury.
Secondary piston (9).
• W ith the rear port plugged apply a small
amount of air pressure to the front port.
(8
Seals and 10).
Spring retainer (7) and spring (
C lean
All the metal parts in denatured alcohol.
All the rubber parts in clean brake fluid.
Stained or discolored cylinder bore with crocus
cloth.

MASTER CYLINDERS

6
s u rfa c e , w h ic h is
6
).
In sp ect
Diaphragm for cuts, cracks, or a swollen condition.
C ylinder bore for scoring or corrosion. If corrosion is
present, replace the cylinder. Do not attem pt to hone
the bore.
Reservoir for cracks.
-► 4-
Install or C o n n ect (F ig u res 9 and 10)
Lubricate the grommets, seals, and cylinder bore
with clean brake fluid.
6
Spring ( ) and spring retainer (7).
Seals (8 and 10) onto the secondary piston (9).
Secondary piston (9).
Prim ary piston assem bly (12).
Snap ring (11).
• The prim ary piston m ust be compressed when
installing the snap ring.
Grommets (4).
Reservoir (3) (figures 12 and 13).
• Press on the body w hile using a rocking
motion.
Diaphragm (2) into the cover (1).
Cover (1).

CAST IRON MASTER CYLINDER

The D elco-M oraine Cast Iron M aster C ylinder has
identifying inform ation stamped into the front outlet tube.
The first and second digits are the build code. The third
digit indicates the year it was built (a 5 means 1985 or a 7
means 1987). The last digits indicate the day it was built
(271 means it was the 271st day of the production year).
NOTICE: Do n o t h one the m a s te r c y lin d e r bore.
When the brake m a ste r c y lin d e r is overhauled,
it is re c o m m e n d e d th a t th e c y lin d e r b o d y be
re p la c e d ra th e r than " c le a n e d u p " by h o n in g
th e bo re. The m a ste r c y lin d e r has a hard, h ig h ly
p o lis h e d " b e a r in g iz e d "
p ro d u c e d b y d ia m o n d b o rin g fo llo w e d b y b a ll o r
ro lle r b u rn is h in g u n d e r heavy pressure. H on in g
w ill d e s tro y th is surfa ce w h ic h w ill cause ra p id
w ear o f ru b b e r cups.
NOTICE: Do n o t use kerosen e, gasoline, o r any
o th e r u n a p p ro v e d s o lv e n ts fo r c le a n in g o r
flu s h in g m a ste r c y lin d e r a nd c o m p o n e n ts . The
use o f these as s o lv e n ts o r any o th e r w ith a
trace o f m in e ra l oil, w ill dam age ru b b e r parts.
R em o ve or D isco nn ect (F ig u re 14)
1. Cover (22).
2. Diaphragm (23).
• Drain all the brake fluid from the reservoir.
3. Snap ring (31).
4. Primary piston assem bly (30) (figure 15).
s u rfa c e , w h ic h is