Jeep Cherokee 1999 Electronic Service Manual page 1405

21 - 82 TRANSMISSION AND TRANSFER CASE
DI AGN OSI S AN D T EST I N G (Cont inue d)
STALL TEST PROCEDURE
(1) Con n ect t a ch om et er t o en gin e. P osit ion t a ch om -
et er so it ca n be viewed fr om dr iver 's sea t .
(2) Dr ive veh icle t o br in g t r a n sm ission flu id u p t o
n or m a l oper a t in g t em per a t u r e. Veh icle ca n be dr iven
on r oa d or on ch a ssis dyn a m om et er, if a va ila ble.
(3) Ch eck t r a n sm ission flu id level. Add flu id if n ec-
essa r y.
(4) Block fr on t wh eels.
(5) F u lly a pply ser vice a n d pa r kin g br a kes.
(6) Open t h r ot t le com plet ely a n d r ecor d m a xim u m
en gin e speed r egist er ed on t a ch om et er. It t a kes 4-10
secon ds t o r ea ch m a x r pm . On c e m a x rp m h a s
be e n a c h ie v e d , d o n o t h o ld w id e o p e n th ro ttle
fo r m o re th a n 4-5 s e c o n d s .
CAUTION: Stalling the converter causes a rapid
increase in fluid temperature. To avoid fluid over-
heating, hold the engine at maximum rpm for no
more than 5 seconds. If engine exceeds 2500 rpm
during the test, release the accelerator pedal imme-
diately; transmission clutch slippage is occurring.
(7) If a secon d st a ll t est is r equ ir ed, cool down
flu id befor e pr oceedin g. Sh ift in t o NE UTRAL a n d r u n
en gin e a t 1000 r pm for 20-30 secon ds t o cool flu id.
STALL TEST ANAL YSIS
Stall Speed Too High
If t h e st a ll speed exceeds 2500 r pm , t r a n sm ission
clu t ch slippa ge is in dica t ed.
Stall Speed Low
Low st a ll speed wit h a pr oper ly t u n ed en gin e in di-
ca t e a t or qu e con ver t er over r u n n in g clu t ch pr oblem .
Th e con dit ion sh ou ld be con fir m ed by r oa d t est in g. A
st a ll speed 250-350 r pm below n or m a l in dica t es t h e
con ver t er over r u n n in g clu t ch is slippin g. Th e veh icle
a lso exh ibit s poor a cceler a t ion bu t oper a t es n or m a lly
on ce h igh wa y cr u ise speeds a r e r ea ch ed. Tor qu e con -
ver t er r epla cem en t will be n ecessa r y.
Stall Speed Normal But Acceleration Poor
If st a ll speeds a r e n or m a l (1800-2300 r pm ) bu t
a bn or m a l t h r ot t le open in g is r equ ir ed for a cceler a -
t ion , or t o m a in t a in cr u ise speed, t h e con ver t er over-
r u n n in g clu t ch is seized. Th e t or qu e con ver t er will
h a ve t o be r epla ced.
Converter Noise During Test
A wh in in g n oise ca u sed by flu id flow is n or m a l du r-
in g a st a ll t est . H owever, lou d m et a llic n oises in di-
ca t e a da m a ged con ver t er. To con fir m t h a t t h e n oise
is or igin a t in g fr om t h e con ver t er, oper a t e t h e veh icle
a t ligh t t h r ot t le in DRIVE a n d NE UTRAL on a h oist
a n d list en for n oise com in g fr om t h e con ver t er h ou s-
in g.
AIR TESTING TRANSMISSION CLUTCH AND
BAND OPERA TION
Air-pr essu r e t est in g ca n be u sed t o ch eck t r a n sm is-
sion fr on t /r ea r clu t ch a n d ba n d oper a t ion . Th e t est
ca n be con du ct ed wit h t h e t r a n sm ission eit h er in t h e
veh icle or on t h e wor k ben ch , a s a fin a l ch eck, a ft er
over h a u l.
Air-pr essu r e t est in g r equ ir es t h a t t h e oil pa n a n d
va lve body be r em oved fr om t h e t r a n sm ission . Th e
ser vo a n d clu t ch a pply pa ssa ges a r e sh own (F ig. 10).
Fig. 10 Air Pressure Test Passages
Front Clutch Air Test
P la ce on e or t wo fin ger s on t h e clu t ch h ou sin g a n d
a pply a ir pr essu r e t h r ou gh fr on t clu t ch a pply pa s-
sa ge. P ist on m ovem en t ca n be felt a n d a soft t h u m p
h ea r d a s t h e clu t ch a pplies.
Rear Clutch Air Test
P la ce on e or t wo fin ger s on t h e clu t ch h ou sin g a n d
a pply a ir pr essu r e t h r ou gh r ea r clu t ch a pply pa ssa ge.
P ist on m ovem en t ca n be felt a n d a soft t h u m p h ea r d
a s t h e clu t ch a pplies.
Front Servo Apply Air Test
Apply a ir pr essu r e t o t h e fr on t ser vo a pply pa s-
sa ge. Th e ser vo r od sh ou ld ext en d a n d ca u se t h e
ba n d t o t igh t en a r ou n d t h e dr u m . Spr in g pr essu r e
sh ou ld r elea se t h e ser vo wh en a ir pr essu r e is
r em oved.
X J