DI AGN OSI S AN D T EST I N G
AUTOMATIC TRANSMISSION
CAUTION: Before attempting any repair on a NAG1
automatic transmission, check for Diagnostic Trou-
ble Codes with the appropriate scan tool.
Transmission m alfunction s may be ca used by these
general condit ions:
• Poor engine performance.
• Improper adjustm ents.
• Hydra ulic malfunct ions.
• Mechan ical malfunctions.
• Electronic malfunct ions.
• Tra nsfer case per formance (if equipped).
Diagnosis of these problems should always begin
by checkin g the easily accessible variables: fluid level
and condition, gearshift cable a djust ment. Then per-
form a road test to deter mine if the problem h as been
correct ed or if mor e diagnosis is necessar y.
PRELIMINARY
Two basic procedu res ar e r equired. One pr ocedure
for vehicles th at are driva ble and an alter nate proce-
du re for disabled vehicles (will not back up or m ove
forwar d).
VEHICLE IS DRIVABLE
(1) Check for tra nsmission fault codes u sing th e
appropriate scan tool.
(2) Check fluid level and condition.
(3) Adjust gearshift cable if compla int was based
on delayed, err atic, or har sh shifts.
(4) Road test and note how tran smission upshift s,
downshifts, an d enga ges.
VEHICLE IS DISABLED
(1) Check fluid level and condition.
(2) Check for broken or disconn ected gearshift
cable.
(3) Check for cracked, lea kin g cooler lines, or loose
or missin g pressur e-port plugs.
(4) Raise and support vehicle on safet y sta nds,
st art engine, shift tr ansmission into gear, and note
following:
(a) If pr opeller shaft turns but wheels do n ot,
pr oblem is with differen tial or axle sha fts.
(b) If propeller shaft does not tur n and tran sm is-
sion is n oisy, stop engine. Rem ove oil pan, and
check for debris. If pan is clear, remove tra nsmis-
sion a nd check for dam aged dr iveplate, conver ter,
oil pu mp, or inpu t shaft.
(c) If propeller sha ft does not t urn and t ransmis-
sion is not noisy, perform hydrau lic-pressure test to
determ ine if problem is h ydraulic or mechanical.
ROAD TESTING
Before roa d testing, be sure th e fluid level an d con-
trol cable adjustm ents have been checked an d
adju st ed if necessar y. Ver ify th at all diagn ost ic trou -
ble codes h ave been resolved.
Observe engine performance dur ing the road test.
A poor ly tuned engine will not allow accur ate ana ly-
sis of tr ansmission opera tion.
Operat e the tra nsmission in all gea r ra nges. Check
for shift variations a nd en gine flare which indicates
slippage. Note if shifts a re harsh, spongy, delayed,
early, or if part t hrottle down shifts ar e sensit ive.
Slippage indica ted by engine flar e, u su ally mean s
clutch, overru nning clu tch, or line pressure problems.
A slipping clutch can often be determ ined by com-
pa ring which internal un its are applied in the va ri-
ous gear ranges. The Clutch Applicat ion cha rt
CLUTCH APP LICATION provides a basis for ana lyz-
ing road test resu lts.
CLU T CH APPLI CAT I ON
GEAR RATIO B1 B2 B3 K1 K2 K3 F1 F2
1 3.59 X* X X* X X
2 2.19 X X X* X
3 1.41 X X X
4 1.00 X X X
5 0.83 X X X X*
N N/A X X
R 3.16 X* X X X
R - Limp In 1.93 X X X
* = The shift components required during coast.
VA AUTOMATIC TRANSMISSION NAG1 - SERVICE INFORMATION 21 - 39
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