Brake Hoses And Lines; Diagnosis And Testing; Base Brake System - Jeep Cherokee 1999 Electronic Service Manual

5 - 6 BRAKES
DESCRI PT I ON AN D OPERAT I ON (Cont inue d)
A pa r kin g br a ke swit ch is m ou n t ed on t h e pa r kin g
br a ke lever a n d is a ct u a t ed by m ovem en t of t h e
lever. Th e swit ch , wh ich is in cir cu it wit h t h e r ed
wa r n in g ligh t in t h e da sh , will illu m in a t e t h e wa r n -
in g ligh t wh en ever t h e pa r kin g br a kes a r e a pplied.

BRAKE HOSES AND LINES

F lexible r u bber h ose is u sed a t bot h fr on t br a kes
a n d a t t h e r ea r a xle ju n ct ion block. Dou ble wa lled
st eel t u bin g is u sed t o con n ect t h e m a st er cylin der t o
t h e m a jor h ydr a u lic br a kin g com pon en t s a n d t h en t o
t h e flexible r u bber h oses.
DI AGN OSI S AN D T EST I N G

BASE BRAKE SYSTEM

Ba se br a ke com pon en t s con sist of t h e br a ke sh oes,
ca liper s, wh eel cylin der s, br a ke dr u m s, r ot or s, br a ke
lin es, m a st er cylin der, boost er, a n d pa r kin g br a ke com -
pon en t s.
Br a ke dia gn osis in volves det er m in in g if t h e pr ob-
lem is r ela t ed t o a m ech a n ica l, h ydr a u lic, or va cu u m
oper a t ed com pon en t .
Th e fir st dia gn osis st ep is t h e pr elim in a r y ch eck.
PRELIMINARY BRAKE CHECK
(1) Ch eck con dit ion of t ir es a n d wh eels. Da m a ged
wh eels a n d wor n , da m a ged, or u n der in fla t ed t ir es
ca n ca u se pu ll, sh u dder, vibr a t ion , a n d a con dit ion
sim ila r t o gr a b.
(2) If com pla in t wa s ba sed on n oise wh en br a kin g,
ch eck su spen sion com pon en t s. J ou n ce fr on t a n d r ea r
of veh icle a n d list en for n oise t h a t m igh t be ca u sed
by loose, wor n or da m a ged su spen sion or st eer in g
com pon en t s.
(3) In spect br a ke flu id level a n d con dit ion . Not e t h a t
t h e br a ke r eser voir flu id level will decr ea se in pr opor-
t ion t o n or m a l lin in g wea r. Als o n o te th a t bra k e flu id
te n d s to d a rk e n o v e r tim e . Th is is n o rm a l a n d
s h o u ld n o t be m is ta k e n fo r c o n ta m in a tio n .
(a ) If flu id level is a bn or m a lly low, look for evi-
den ce of lea ks a t ca liper s, wh eel cylin der s, br a ke
lin es, a n d m a st er cylin der.
(b) If flu id a ppea r s con t a m in a t ed, dr a in ou t a
sa m ple t o exa m in e. Syst em will h a ve t o be flu sh ed
if flu id is sepa r a t ed in t o la yer s, or con t a in s a su b-
st a n ce ot h er t h a n br a ke flu id. Th e syst em sea ls
a n d cu ps will a lso h a ve t o be r epla ced a ft er flu sh -
in g. Use clea n br a ke flu id t o flu sh t h e syst em .
(4) Ch eck pa r kin g br a ke oper a t ion . Ver ify fr ee
m ovem en t a n d fu ll r elea se of ca bles a n d peda l. Also
n ot e if veh icle wa s bein g oper a t ed wit h pa r kin g
br a ke pa r t ia lly a pplied.
(5) Ch eck br a ke peda l oper a t ion . Ver ify t h a t peda l
does n ot bin d a n d h a s a dequ a t e fr ee pla y. If peda l
la cks fr ee pla y, ch eck peda l a n d power boost er for
bein g loose or for bin d con dit ion . Do n ot r oa d t est
u n t il con dit ion is cor r ect ed.
(6) Ch eck boost er va cu u m ch eck va lve a n d h ose.
(7) If com pon en t s ch ecked a ppea r OK, r oa d t est
t h e veh icle.
ROAD TESTING
(1) If com pla in t in volved low br a ke peda l, pu m p
peda l a n d n ot e if it com es ba ck u p t o n or m a l h eigh t .
(2) Ch eck br a ke peda l r espon se wit h t r a n sm ission
in Neu t r a l a n d en gin e r u n n in g. P eda l sh ou ld r em a in
fir m u n der con st a n t foot pr essu r e.
(3) Du r in g r oa d t est , m a ke n or m a l a n d fir m br a ke
st ops in 25-40 m ph r a n ge. Not e fa u lt y br a ke oper a -
t ion su ch a s low peda l, h a r d peda l, fa de, peda l pu lsa -
t ion , pu ll, gr a b, dr a g, n oise, et c.
(4) At t em pt t o st op t h e veh icle wit h t h e pa r kin g
br a ke on ly a n d n ot e gr a b, dr a g, n oise, et c.
PEDAL FALLS A WA Y
A br a ke peda l t h a t fa lls a wa y u n der st ea dy foot
pr essu r e is gen er a lly t h e r esu lt of a syst em lea k. Th e
lea k poin t cou ld be a t a br a ke lin e, fit t in g, h ose, or
ca liper /wh eel cylin der. If lea ka ge is sever e, flu id will
be eviden t a t or a r ou n d t h e lea kin g com pon en t .
In t er n a l lea ka ge (sea l by-pa ss) in t h e m a st er cylin -
der ca u sed by wor n or da m a ged pist on cu ps, m a y
a lso be t h e pr oblem ca u se.
An in t er n a l lea k in t h e ABS or RWAL syst em m a y
a lso be t h e pr oblem wit h n o ph ysica lly eviden t .
LOW PEDAL
If a low peda l is exper ien ced, pu m p t h e peda l sev-
er a l t im es. If t h e peda l com es ba ck u p wor n lin in gs,
r ot or s, dr u m s, or r ea r br a kes ou t of a dju st m en t a r e
t h e m ost likely ca u ses. Th e pr oper cou r se of a ct ion is
t o in spect a n d r epla ce a ll wor n com pon en t a n d m a ke
t h e pr oper a dju st m en t s.
SPONGY PEDAL
A spon gy peda l is m ost oft en ca u sed by a ir in t h e
syst em . H owever, t h in br a ke dr u m s or su bst a n da r d
br a ke lin es a n d h oses ca n a lso ca u se a spon gy peda l.
Th e pr oper cou r se of a ct ion is t o bleed t h e syst em ,
a n d r epla ce t h in dr u m s a n d su bst a n da r d qu a lit y
br a ke h oses if su spect ed.
HARD PEDAL OR HIGH PEDAL EFFORT
A h a r d peda l or h igh peda l effor t m a y be du e t o
lin in g t h a t is wa t er soa ked, con t a m in a t ed, gla zed, or
ba dly wor n . Th e power boost er or ch eck va lve cou ld
a lso be fa u lt y.
PEDAL PULSA TION
P eda l pu lsa t ion is ca u sed by com pon en t s t h a t a r e
loose, or beyon d t oler a n ce lim it s.
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