slice, direction of which is opposite
to direction of the wheel turning. Di鄄
rection of moment produced by fric鄄
tion force on the font shoe is as
same as direction of the push force,
and they both press to the brake
drum, which increases braking effi鄄
ciency of the front shoe and assists
power, so the front brake shoe is
called power -assisted brake shoe;
while direction of moment produced
by friction force on the rear shoe is
just opposite to direction of the push
force, which decreases pressure that
brake shoe applies on brake drum,
so that braking efficiency of the rear
shoe decreases resulting in power
reducing, so the rear brake shoe is
called power -reducing brake shoe.
All above leads to imbalance of
forces that front and rear brake
shoes press on the brake drum, so
this kind of brake is called simple
imbalanced brake.
Clearance between friction disc of the
brake shoe and the brake drum must
be proper, before adjusting the clear鄄
ance, make the front wheel off ground;
adjusting steps are as follows:
Turn worm of the brake arm to adjust
clearance between friction disc at the
camshaft end of the brake assembly
and the brake drum. Adjusting meth鄄
ods are as follows: Face to the worm,
turn the worm clockwise, at the same
time, rotate the brake drum come -
and -go continuously till the brake
drum is suppressed completely, and
then return the worm anticlockwise
by 1/2 -3/4 circle, at this time,
windage of the end of the ed of the
brake drum shaft is 0.25 -0.4mm,
while camshaft end 0.45mm. After
adjusting, do test -drive to check
working condition of the brake and
whether the brake drum heats and
whether the braking distance is prop鄄
er, if not, readjust the vehicle.
2.1.5 Brake valve
Brake valve is a mechanism with
which the whole air brake system
controls the brake.
2.1.6 Maintenance
2.2 Before running, air pressure in
the pipeline should be checked,
when the air pressure is more than
0.6Mpa, the vehicle can start, and
56
the normal running air pressure is
0.74-0.84Mpa; if the air pressure is
lower than this value, check the air
pipeline for leak and check whether
the air compressor works normally.
2.3 Check working condition of the
brake in running whether there is any
trailing or the braking cannot return
and deal with the problems in time. If
the air pressure is lower than
0.45Mpa but the annuciator does not
warn, check the annuciator, replace
if necessary.
2.4 If the brake shoe slice is dam鄄
aged or over worn, replace for new
one; surface of the new liner should
be grinded, and there should be no
oil dirt, scratches, chap on the sur鄄
face. Friction disc must be made of
the same material.
Replacing friction disc or reinstalling
shoe slice shaft and brake camshaft
will damage contact condition be鄄
tween former friction disc and brake
drum, because of which, complete
adjustment must be done.
2.2 Hydraulic brake
1) Brief description of structure
Service brake of trucks of HFC1045
series adopts hydraulic brake and is
mainly composed of vacuum boost鄄
er, vacuum tank, brake master cylin鄄
der,
control
mechanism,
brake
pipeline, front & rear brake, and is
reliable and safe as well as operates
lightly, reacts agilely, etc.
When depress the service brake
pedal, if you feel the braking is weak,
but the brake liquor is sufficient, the
cause of ineffective braking maybe
that there is air in the brake system,
and the air should be deflated ac鄄
cording to the following sequence:
right rear wheel brake - left rear
wheel brake - right front wheel
brake- left rear wheel brake. Method
of air deflation is as follows:
a. Clean up begrime on deflating
screw of the brake master cylinder
and release cylinder
b. Unscrew screw plug of the filling
opening of master cylinder or fluid
pot, and fill brake fluid to full position.
c. After depressing brake pedal sev鄄
eral times continuously, depress e鄄
mergency brake pedal, and loose
deflating bolt to deflate air; repeat
57
HFC1045
series trucks