Advertisement
(253)
BRAKES
TROUBLE DIAGNOSIS
8-9
8-8) and check for springy pedal action (sub-
par. b, below).
(3) Air in Hydraulic System. Air in hy-
draulic system will cause a springy action of
brake pedal.
If
volume of air is large, the pedal
will go to toeboard under normal pressure.
Bleed hydraulic system (par.
8-9).
(4) Fluid Leak in Hydraulic System. A leak
in the hydraulic system will allow the pedal to
go to the toeboard gradually under continued
pressure. An external leak is indicated by loss
of fluid in fluid reservoir. Check all brake pipe
connections and all wheel cylinders for evidence
of fluid loss.
If
no leaks are found, remove mas-
ter cylinder and check for scores or other
dam-
age in barrel and on primary cup (par.
8-19).
b. Springy, Spongy Action of Brake Pedal
(1)
Air in Hydraulic System. Air in system
is usually caused by operating brake pedal with
low fluid level in master cylinder reservoir : how-
ever, air will also enter the system whenever
any part of hydraulic system is disconnected.
Fill reservoir and bleed hydraulic system (par.
8-9) .
(2) Brake Shoes not Properly Adjusted. Ad-
just brake shoes, paying particular attention
to obtaining uniform clearances and correct
anchor pin location (par. 8-15).
(3) Brake Drum Out of Round. Usually in-
dicated by an unstable action of brake pedal.
Check brake drums and true up if necessary
(par. 8-17).
c. Brakes Severe on Light Pedal Pressure
(1)
Brake Shoes not Properly Adjusted. Ad-
just brake shoes, paying particular attention to
obtaining uniform clearances and correct an-
chor pin location (par. 8-15).
(2) Faulty Brake Linings or Drums. A small
amount of grease or brake fluid on lining will
cause grabbing action. Correct the cause and
replace lining since these substances cannot be
permanently cleaned out of lining (par. 8-16).
Charred linings or scored drums cause
grab-
bing action. Replace linings and true up drums
(par. 8-17).
(3) Loose Front Wheel Bearings. Check for
play in bearings with wheels jacked up and
adjust if necessary (par. 6-14).
(4) Loose Brake Backing Plate. Tighten all
backing plates and adjust brake shoes to proper
clearance (par. 8-15).
d. Excessive Pedal Pressure Required
(1)
Brake Shoes Not Properly Centered.
If
brake shoes are not concentric with drums they
will not make full contact and braking area
will be reduced. Adjust brake shoes, paying
particular attention to obtaining uniform clear-
ance and correct anchor pin location (par.
8-15) .
(2) Foreign Substances on Linings. Grease,
oil, paint, or other foreign substances on lin-
ings will reduce their gripping qualities and
require excessive pedal pressure to stop the
car. Replace faulty linings (par. 8-16).
(3) Improper Brake Lining. Improper grades
of lining lose their gripping qualities after some
use. Replace with genuine Buick lining (par.
8-16) .
e. Brakes Drag at One Wheel
(1)
Brake Shoes Have Insufficient Clearance.
Check clearance with feeler gauge and adjust
brake shoes if necessary (par. 8-15).
(2)
Weak or Broken Brake Shoe Spring.
Does not allow proper releasing of brake shoes.
Replace spring and check brake shoe adjust-
ment (par. 8-15).
(3) Loose Front Wheel Bearings. Check for
play in bearings with wheel jacked up and ad-
just if necessary (par. 6-14).
(4) Wheel Cylinder Piston Stuck or Cups
Distorted. May be caused by dirt in hydraulic
fluid, improper fluid, or previous use of a clean-
ing fluid which is detrimental to rubber
parts.
Overhaul wheel cylinder and replace any defec-
tive parts (par. 8-18). It is also advisable to
flush hydraulic system to prevent repetition of
trouble (par. 8-10).
(5)
Obstruction in Brake Pipes or Hoses.
Obstruction may be caused by foreign material.
damaged pipe, kinked or deteriorated brake
hose. Flush hydraulic system (par. 8-10) or re-
place damaged or defective part as required.
f. Brakes Drag at All Wheels
(1)
Insufficient Clearance at Brake Shoes.
Check clearance with feeler gauge and adjust
brake shoes if necessary (par. 8-15).
(2)
111 aster Cylinder Compensating Port
Closed.
If
the compensating port is plugged by
foreign material, or is covered by the piston
primary cup when brake pedal is in released
position, high pressure will be maintained in
hydraulic system and brake shoes will be held
in contact with drums. This condition is indi-
cated by lack of normal pedal travel and a very
solid feel when pedal is depressed.
Check brake pedal adjustment (par. 8-11).
Make certain that pedal is free on shaft and
Advertisement
