Chevrolet 1977 light duty truck, Service Manual

Page: 409 / 861

Fig. 5-1 5 -D e lco Secondary Piston - Exploded View
insure a d e q u a te reserve and to prevent air from entering
the hydraulic system. However, because o f expansion due
to heat abso rb ed from brakes and from engine, master
cylinder must not be overfilled.
T h e brake fluid reservoir is on the m aster cylinder
which is located u n d e r the hood on the left side o f the
dash.
T h o ro u g h ly clean reservoir cover before removal to
avoid getting dirt into reservoir. Remove cover and
d ia p h ra g m . A dd fluid as required to bring level to 1 /4 "
(plus o r minus 1 /8 " ) from the lowest portion o f the top
o f each reservoir. Use Delco S uprem e No. 11 Hydraulic
Brake Fluid o r equivalent.
D o not use shock ab so rb er fluid or any other fluid
which contains m ineral oil. Do not use a container which
has b een used for m ineral oil or a co n tain er which is wet
from water. M ineral oil will cause swelling and distortion
o f ru b b e r parts in the hydraulic brake system and w ater
will mix with brake fluid, lowering the fluid boiling
point. Keep all fluid containers capped to prevent w ater
contam ination.
Except Bendix Mini-Master Cylinder
Removal
1. Disconnect brake pipes from m aster cylinder
and tape end o f pipes to prevent entrance o f dirt.
2.
M anual brake
only-D isconnect brake pedal
from m aster cylinder push rod.
3. R em ove two nuts holding m aster cylinder to
dash o r power cylinder and remove master cylinder from
vehicle. Be careful not to d rip brake fluid on exterior
paint.
Disassembly (Figs. 5 -1 4 and 5 -1 5 )
1. Clean outside o f m aster cylinder thoroughly.
Remove reservoir cover and d ia p h ra g m . T u rn cylinder
over an d p u m p push rod by h a n d to d ra in all brake
fluid. Always discard used fluid.
2.
M anual brake
only-Pull boot away from m aster
cylinder to uncover push rod retainer. The re ta in e r has a
small, depressed tab in the side. This tab must be pried
up to release retainer.
3. Depress piston and remove secondary piston
stop bolt from bottom o f front fluid reservoir (if so
equipped).
4. Place m aster cylinder in a vise so th at lock ring
can be removed fro m groove in the inside d iam eter o f
bore. Remove lock ring an d p rim a ry piston assembly.
Remove secondary piston, secondary piston spring and
retain er by blowing air through the outlet port.
5. Place m aster cylinder in vise, so that outlet holes
are up. Enlarge hole in tube fitting insert using a 13/64"
drill. Place a heavy w asher over outlet on m aster cylinder
and thread a 1/4-20 x 3 / 4 " screw into the insert. Tighten
screw until insert is unseated. Remove insert, screw, and
washer.
6. Remove p rim a ry seal, an d secondary seal from
secondary piston.
7. Use clean brake fluid to clean all metal brake
parts thoroughly. A ir dry and place cleaned parts on
clean p a p e r or lint free clean cloth.
Do not use anti-freeze alcohol, gasoline, kerosene,
or any other cleaning fluid th at m ight contain even
a trace o f m ineral oil.
Inspection
Inspect cylinder bore for scoring or corrosion. It is
best to replace a corroded cylinder. C orrosion can be
identified as pits or excessive roughness.
Polish any discolored or stained area with crocus
cloth by revolving cylinder on cloth supported by finger.
Rinse cylinder in clean brake fluid. Shake excess
rinsing fluid from cylinder. Do not use a rag to dry
cylinder, as lint from rag cannot be kept from cylinder
bore surfaces.
M ake certain that com pensating port in cylinder is
clear.
If scratches or corroded spots are too d eep to be
polished satisfactorily, the cylinder should be replaced.
Assembly
1. Place brass tube fitting insert (new parts) in
outlet holes so that it is in a position to be pressed into
outlet hole. T he reco m m en d ed method o f inserting tube
fitting insert is to thread a spare brake line tube nut into
outlet hole and turn nut down until tube fitting insert
bottoms. Remove tube nut and check outlet hole for
loose burrs, which m ight have been turned up when tube
fitting insert was pressed down.
2. Put new secondary seal in groove in end o f
secondary piston (fig. 5-15).
3. Assemble a new p rim a ry seal over end o f
secondary piston, so that flat side o f the seal seats
against flange o f piston (fig. 5-15).
4. Assemble new secondary seal into groove on end
o f the secondary piston.
5. In o rd er to insure correct assembly o f the
p rim ary assembly, a complete p rim a ry piston assembly is
included in the rep air kits.
6. Coat bore o f m aster cylinder with clean brake