1988 PONTIAC FIERO Service Repair Manual

70bR4-28 HYDRAULIC DIAGNOSIS
D-4 SECOND GEAR
(CONVERTER SIGNAL OIL)

HYDRAULIC DIAGNOSIS 700.R4.29
CO#YEA'TER CLUTCH - APPUEO
FDRWMO CLUTCtl - APPUED
D-4-SECOND GEAR
I Converter Signal 011 1
2-4 BAMD - APPLIED
FORWARD SWAG CLUTCH - HOLDiNQ
NON EC.M. CONTROLLED VEHICLES
As vehicle speed and governor pressure increase, the force of the governor oil acting on the converter
clutch shift valve overcomes the pressure of M.T.V. up oil and the force of the converter clutch T.V.
spring. This allows the converter clutch shift valve to open and 2nd oil to enter the converter clutch
signal
passaga Converter signal oil will exhaust at the T.C.C. sotenoid until a signal is received from
the vehicles external controls.
E.C.M. CONTROLLED VEHICLES
Second oil 'is rerouted into converter clutch signal oil at the bore plugs used in place of the converter
clutch shift valve. Conwrter signal oil exhausts at this solenoid until a signal is received from the vehicles
EC.M.
JHOl7klW14
Figure 26 I14 - Second Gear - Converter Signal Oil

0044.30 HYDRAULIC DIAGNOSIS
D-4 THIRD GEAR -
-lmAwh-
(CONVERTER cum+ APPLIED)
JHOO22-7OOR4
Figure 27 04 -Third Gear - Converter Clutch Applied

HYDRAULIC DfAQNOSIS 70044-31
As both vehicle speed and governor pressure increase, the force of gowrnor oil acting on the 2-3
shift valve overcomes the force of the 2-3 T.V. spring and MXV. up oil, This allows the 2-3 shift valve
to
open and allows RN04D3 oil to enter the 3rd clutch passage.
Third clutch oil from the 2-3 shift valve is directed to the following:
1. 3-2 Exhaust Checkball (4)
2. 3-4 Clutch Piston
3. Third Clutch Accumulator Checkball (2)
4. Third Accumulator Exhaust: Checkball (7)
6. 2-4 Servo 1Release Side)
6. 3-2 Control Valve
D-4-THIRD GEAR
[Converter CItPtch Applied)
COMVERTER CtUTCli - APPLIED FOAWARD CLUTCH - APPLIED
FORWARD SFRAG CLU7CH - HPLDINO 34 CLUTCH - APPLIED
Third clutch oil from the 2-3 shift valve flows past the 3-2 exhaust checkball (4), to the 3-4 clutch
piston. At the same time, third clutch oil is directed past the third clutch accumulator checkball {2),
seats the third accumula'tor exhaust check ball (71, and then into the release side of the 2-4 serva
This third clutch accumulator pressure combined with the servo cushion spring, moves the second
apply piston, in the 2-4 servo, against second oil and acts as an accumulator for a smooth 2-4 band
release and 3-4 clutch apply.
Third clutch oil is present at the 3-2 control valve In preparation of a third gear to second gear shift.
Once the solenoid teceives a signal from the vehicles controls and solenoid is on, convefier clutch
signal oil will shift the converter clutch apply valve, and redirect converter feed oil into the apply passage.
the apply oil flows between the stator shaft and converter hub to charge the converter with oil and
push the converter pressure plate against the converter cwer, causing a mechanical link between
the engine and the turbhe shaft. The rate of apply is controlled by the orifice checkball capsule in
tha end of the turbine shaft.
At tho same time the converter clutch appfy valve will direct converter feed oil through an orifice to
the transmission cooler. Cooler oil is directed to the transmission lubrication sysm.
SUMMARY
The converter clutch is applied*, the forward clutch is applied, tho forward sprag clutch is holding,
the 3-4 clutch is applied and the 2-4 band is released; the transmission is in Drive (Dl Range - Third
Gear (direct drive).
+The converter clwh msy or may not be applied, depending on Aitt calibration and salenoid operation. JHOI 80+7OOA4
Figure 28 D4 - Third Gear - Converter Clutch Applkd

700.R4-32 HYDRAULIC DlAGNOSlS
D-4 OVERDRIVE
ILI.
I J%002a7rnI I
Figure 29 04 - Overdrive

D-4- OVERDRIVE
HYDRAUUC DIAGNOSIS 70044-33
CONVERTER CLUTCH - APPLIED 9-4 CLUKH - APPLIED 24 3AlD - APPLIED
FORWARO CLUTCH - APPLIED FORWARD SPRM CLUTCH - HOT HOLDlNO
As both vehlcle speed and governor pressure incwaae, the force of governor oil acting on the 3-4
shift valve overcomes the force of the 3-4 T.V, spring and M.T.V. up oil. This opens the 3-4 shift valve
sending Drive 4 lD41 into the fourth signal passage. Fourth signal oil will overcome the 4-3 sequence
valve spring and open the 3-4 relay and the 4-3 sequence valves, allowing second oil to enter the
servo feed passage.
Servo feed oil is directed to the following:
1. 2-3 Shift Valve
a. Which directs oil to the:
1) 3-4 Accurnuiator
2) 4-3 Sequence Valve
2. 4-3 Sequence hive
a. Which directs oil to the:
1) 4th Apply Piston (in the 2-4 servo)
SUMMARY
The converter clutch, 24 band, forward clutch, the 3-4 clutch an applied, and the forward sprag
clutch is werrunning; the transmission is in Drive (D) Range - Overdrive,
*Tha converter clutch may or may not ba applied, depending on denoid operation.
JHOI er.?ow
Figure 30 b4 - Overdrive
BASIC CONTROL
Servo feed oil passes through the 4-3 sequence valve and becomes fourth oil. Fourth oil then enters
the
2-4 servo, applies pressure on the fourth apply piston, and applles the 2-4 band.

1 lcHpP24.7 00R4 I Figure 3 1 Part Throttle 43 and Modulated Downshifts, Valves Shown in Third Gear Position

HYDRAULIC DIAGNOSIS 700.R4-35
COlVUlTER CLUfefl - APPLIED
FORWARD SPRAG CLUTCH - HOLDING
FORWARD CLUTCH - APPLIED
3-4 CLUTCH - APPLIED
A part throttle 4-3 downshift can be accomplished by depressing the accelerator pedal far enough
to move the throttle va!ve (T.V.) plunger to allow the T.V. oil to enter the part throttle (PT.1 passage.
This oit, called part throttle (P.T.) oil, is then routed to the 3-4 throttle valve.
Part throttle oil and the 34 throttle valve spring force wilt close the 3-4 shift valve against governor
pressure, shutting
off D4 oil to the fourth signal passage. Fourth accumulator oil will push the 3-4
relay valve closed and hold the 4-3 sequence valve open while it exhausts at an orifice at the T.V.
limit valve. Fourth oil will pass through the 4-3 sequence valve to the servo feed passage to the 2-3
shift valve to the fourth accumulator passaga When fourth accumulator pressure is low enough, the
4-3 sequence valve spring will close the 4-3 sequence valve and the remaining fourth and fourth
eccumulator oil will exhaust at the 4-3 sequence valve.
A type of part throttle downshift can be accomplished in some ranges (4-3, and 3-2, shifts) by
depressing the accelerator pedal far enough to raise M.T.V. down pressure. This pressure when com-
bined with the throttle valve spring pressure can wercome governor pressure and cause a modulated
downshift
'The converter clutch may or may not be applied depending on shift calibration and solenoid operation.
I JH0182JOOR4 1 Figure 32 Part Throttle 4-3 and Modulated Downshifts