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DR
AUTOMATIC TRANSMISSION - 48RE (Continued)
(3) Have helper start and run engine at 1600 rpm
for test.
(4) Move transmission shift lever four detents
rearward from full forward position. This is Reverse
range.
(5) Move transmission throttle lever fully forward
then fully rearward and note reading at Gauge
C-3293-SP.
(6) Pressure should be 145 - 175 psi (1000-1207
kPa) with throttle lever forward and increase to 230 -
280 psi (1586-1931 kPa) as lever is gradually moved
rearward.
Test Five - Governor Pressure
This test checks governor operation by measuring
governor pressure response to changes in vehicle
speed. It is usually not necessary to check governor
operation unless shift speeds are incorrect or if the
transmission will not downshift. The test should be
performed on the road or on a hoist that will allow
the rear wheels to rotate freely.
(1) Move 100 psi Test Gauge C-3292 to governor
pressure port.
(2) Move transmission shift lever two detents rear-
ward from full forward position. This is D range.
(3) Have helper start and run engine at curb idle
speed. Then firmly apply service brakes so wheels
will not rotate.
(4) Note governor pressure:
• Governor pressure should be no more than 20.6
kPa (3 psi) at curb idle speed and wheels not rotat-
ing.
• If pressure exceeds 20.6 kPa (3 psi), a fault
exists in governor pressure control system.
(5) Release brakes, slowly increase engine speed,
and observe speedometer and pressure test gauge (do
not exceed 30 mph on speedometer). Governor pres-
sure should increase in proportion to vehicle speed.
Or approximately 6.89 kPa (1 psi) for every 1 mph.
(6) Governor pressure rise should be smooth and
drop back to no more than 20.6 kPa (3 psi), after
engine returns to curb idle and brakes are applied to
prevent wheels from rotating.
(7) Compare results of pressure test with analysis
chart.
Test Six - Transmission In Overdrive Fourth Gear
This test checks line pressure at the overdrive
clutch in fourth gear range. Use 300 psi Test Gauge
C-3293-SP for this test. The test should be performed
on the road or on a chassis dyno.
(1) Remove tachometer; it is not needed for this
test.
(2) Move 300 psi Gauge to overdrive clutch pres-
sure test port. Then remove other gauge and reinstall
test port plug.
AUTOMATIC TRANSMISSION - 48RE
(3) Lower vehicle.
(4) Turn OD switch on.
(5) Secure test gauge so it can be viewed from
drivers seat.
(6) Start engine and shift into D range.
(7) Increase vehicle speed gradually until 3-4 shift
occurs and note gauge pressure.
(8) Pressure should be 524-565 kPa (76-82 psi)
with closed throttle and increase to 690-896 kPa
(100-130 psi) at 1/2 to 3/4 throttle. Note that pres-
sure can increase to around 965 kPa (140 psi) at full
throttle.
(9) Return to shop or move vehicle off chassis
dyno.
PRESSURE TEST ANALYSIS CHART
TEST CONDITION
Line pressure OK during
any one test
Line pressure OK in R but
low in D, 2, 1
Pressure low in D Fourth
Gear Range
Pressure OK in 1, 2 but
low in D3 and R
Pressure OK in 2 but low
in R and 1
Front servo pressure in 2
Pressure low in all
positions
Governor pressure too
high at idle speed
Governor pressure low at
all mph figures
Lubrication pressure low
at all throttle positions
Line pressure high
Line pressure low
21 - 323
INDICATION
Pump and regulator valve
OK
Leakage in rear clutch
area (seal rings, clutch
seals)
Overdrive clutch piston
seal, or check ball
problem
Leakage in front clutch
area
Leakage in rear servo
Leakage in servo; broken
servo ring or cracked
servo piston
Clogged filter, stuck
regulator valve, worn or
faulty pump, low oil level
Governor pressure
solenoid valve system
fault. Refer to diagnostic
book.
Faulty governor pressure
solenoid, transmission
control module, or
governor pressure sensor
Clogged fluid cooler or
lines, seal rings leaking,
worn pump bushings,
pump, clutch retainer, or
clogged filter.
Output shaft plugged,
sticky regulator valve
Sticky regulator valve,
clogged filter, worn pump
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