Light Scoring; Checking Lateral Runout; Checking Parallelism; Master Cylinder - Typical - Chevrolet CHEVY VAN G10 SERIES Service Manual

Light Scoring

Light scoring o f the disc surfaces n o t exceeding .015 inch in
dep th , w hich m ay result from norm al use, is n o t detrim ental
to brake operation.

Checking Lateral Runout

Tighten the wheel bearing adjusting nut until all o f the play
is out o f the bearing. I t should be ju st loose enough to allow
the wheel to tu rn . F asten a dial indicator to some po rtion of
the suspension so th a t the po in t o f the stylus co ntacts the
ro to r face approxim ately one inch from the ro to r edge. Set the
dial at zero and move the ro to r one com plete ro tatio n ,
checking the indicator as the ro to r moves. A fter checking the
ru n o u t, readjust the w heel bearing (See Section 3).

Checking Parallelism

To check for parallelism , m easure the thickness o f the roto r
at four or m ore points around the circum ference o f the ro to r.
All m easurem ents m ust be m ade at the same distance in from
the edge o f the ro to r.
MASTER C Y LIN D E R (Fig. 40)
C A U T IO N : Always use denatured alcohol or brake
flu id to clean any master cylinder parts. Never use
mineral-base cleaning solvents such as gasoline, kero­
sene, carbon-tetrachloride, acetone, paint thinner or
units of like nature as these solvents deteriorate
rubber parts, causing them to become soft and
swollen in an extrem ely short tim e.
Removal
1. Wipe m aster cylinder and lines clean w ith a clean cloth.
Place dry cloths below m aster cylinder area to absorb any
fluid spillage.
2. D isconnect hydraulic lines at m aster cylinder. Cover line
Fig. 4 0 —Master C ylinder - Typical
ends w ith clean lint-free m aterial to prevent foreign
m atter from entering the system .
3. D isconnect the push rod from the brake pedal.
4. U nbolt and remove the m aster cylinder from the dash
panel or pow er brake booster.
Disassembly (Fig. 41)
1. Remove the small secondary p iston stop screw from the
b o tto m o f the front fluid reservoir o f the m aster
cylinder.
2. Place the m aster cylinder in the vise so th a t the lock ring
can be rem oved from the small groove in the I.D . o f the
bore. Remove the lock ring and prim ary piston assembly.
Remove the secondary piston, secondary piston spring
and retainer by blow ing air through the stop screw hole.
If air is n o t available, a piece o f wire may be used. Bend
approxim ately 1 /4" o f one end o f the wire in to a right
angle. H ook this end under the edge o f the secondary
piston and pull the secondary piston from the bore.
C A U T IO N : Do not clamp vise too tightly as dam ­
age to the master cylinder could result.
N O T E : The brass tube-fitting insert should N O T
be removed unless visual inspection indicates the
insert is damaged.
3. To replace a defective insert the following procedure
should be practiced:
a. Place the m aster cylinder in a vise, so th a t the outlet
holes are u p. Enlarge the outlet holes in the tube
seats using a 1 3 /6 4 " drill. Tap a l / 4 " -20 thread in
these holes. Place a heavy washer over the outlet on
the m aster cylinder and th read a 1/4" - 20 x 3 /4 "
hex head b o lt in to the tube seat. Tighten the bolt
until the tube seat is unseated.
b. A m ore preferable w ay to remove a defective insert
involves use o f a self-tapping screw and a claw
BRAKES 5-21
C H E V Y V A N SH O P M A N U A L