GMC 1986 P-Truck Service Manual page 421

The following notice applies to one or more steps in the assembly procedure of components in this portion of the
manual as indicated at appropriate locations by the terminology NOTICE: See 'Notice' on page 5-1 of this section.
NOTICE: This fastener is an important attaching part in that it could affect the performance of vital compo­
nents and system, and/or could result in major repair expense. It must be replaced with one of the same part
number or with an equivalent part if replacement becomes necessary. Do not use a replacement part of
lesser quality or substitute design. Torque values must be used as specified during reassembly to assure
proper retention of this part.
CAUTION: When servicing wheel brake parts, do not create dust by grinding or sanding brake linings or by
cleaning wheel brake parts w ith a dry brush or w ith compressed air. (A water dampened cloth should be
used). Many wheel brake parts contain asbestos fibers which can become airborne if dust is created during
servicing. Breathing dust containing asbestos fibers may cause serious bodily harm.
SUBJECT
Brake System D ia g n o s is .............................................................................................................................................5 - 2
Road Testing the B ra k e s ........................................................................................................................................ 5 - 2
Hydro-Boost System T e s t s .................................................................................................................................... 5 - 2
Diagnosis o f Brake S y s te m ........................................................................................................................................ 5 - 4
Diagnosis o f Hydro-Boost S y s te m ........................................................................................................................... 5 - 7
On - Vehicle S ervice..................................................................................................................................................... 5 -
Bleeding the Brake Hydraulic S y s te m .................................................................................................................5 - 8
Flushing the Brake Hydraulic S ystem ...................................................................................................................5 - 9
Brake Pipes and H o s e s ...........................................................................................................................................5 - 9
Com bination V a lv e ................................................................................................................................................... 5-12
Height Sensing Brake P roportioning V a lv e ........................................................................................................5-13
Brake Pedal A sse m b ly................................................................................................................................................. 5-17
Checking Pedal T ra v e l.............................................................................................................................................5-17
Brake Pedal R e p la ce m e n t...................................................................................................................................... 5-17
Brake Pedal Rod R e p la ce m e n t............................................................................................................................. 5-20
Stoplamp S w itc h ....................................................................................................................................................... 5-20
Parking Brake S y s te m ................................................................................................................................................. 5-22
Parking Brake Pedal or Handle R e p la c e m e n t................................................................................................... 5-22
Cable R eplacem ent................................................................................................................................................... 5-23
Propeller Shaft Brake R e p la ce m e n t.....................................................................................................................5-27
Parking Brake A d ju s tm e n t...................................................................................................................................... 5-27
Master C ylinders............................................................................................................................................................5-30
D e s c rip tio n ................................................................................................................................................................ 5-30
Master Cylinder R e p la ce m e n t................................................................................................................................5-30
Bench B le e d in g ..........................................................................................................................................................5-30
Vacuum B o o s te rs ..........................................................................................................................................................5-32
D e s c rip tio n ................................................................................................................................................................ 5-32
Vacuum Booster R e p la c e m e n t............................................................................................................................. 5-32
SECTION 5
BRAKES
CONTENTS
5-1
PAGE
8