1988 PONTIAC FIERO Service Repair Manual

700.R4-31 HYDRAULIC DIAGNOSIS
I JHW257WR4 I Figure 33 Detent Downshifts, Valves Shown in Second Gear Position

HYDRAULIC DIAGNOSIS 7004437
COIYVEIWER CLUTCH - RELEASED
FORWARD CLUltH - APPUEO
DETENT DOWNSHIFTS
1Valves In Second Gear Position)
2.4 BAND - APPLIED
FORWARD
SPRAQ CLUTCH - HOLDING
While operating at speeds below approximately 60 mph (96 kmth), a forced or detent 3-2 downshift
is possible by dapressing the accelerator pedal fully. This will position the throttle valve {T.V.}
plunger to allow T.V. oil to enter the detent passage. This oil, called detent oil, is then routed to
the following:
I. Line Bias Valve
2. 2-3 Throttle Valve
3. 1-2 Throttle Valve
4. Converter Clutch Throttle Valve (Non EC.M. Controlled Vehicles Only}
Detent ail from the T.V. plunger flows to the line bias valve to boost modulated T.V. (M.T.V.1 pressure.
M.T.V. oil acting on the T.V. boost valve will boost line pressure approximately 70 kPa (10 psi).
NON E.C.M. CONTROLLED VEHICLES
Detent oil at the cmverter clutch throttle valve will close the converter clutch shift valve train and
release the converter clutch.
E.C.M. CONTROLLED VEHCLES
The E.C.M. wll discontinue the signal provided to the solenoid to release the converter ctutch.
Dstent oil from the 7.V. plunger flows to the 2-3 throttle valve. Detent and M.T.V. down ol, acting
on separate
areas of the 2-3 throttle valve, will close the 2-3 shift valve against governor oil and allow
3rd clutch and 3rd accumulator oil to pass through an orifice and exhaust at the 2-3 shift valve.
At vehicle speeds above approximately 50 rnph (80 km/h), governor oil acting on the 3-2 control valve
will close it. Now the exhausting 3rd clutch accumulator oil from the inxemediate servo will seat the
3rd clutch accumulator checkball
(21 and low through another orifi~e controlling the intermediate
band apply for
a smooth 3-2 shift at high speed.
A detsnt 2-1 downshift can be accomplished at speeds below approximately 30 mph 148 krnlh),
because detent oil pressure and the 1-2 spring force acting on the 1-2 throttle valve will close the
1-2 shift valve, shifting the transmission to first gear.
JH018S-700A4
Figure 34 Deterit Downshifts

70044.38 HY DRAULfC DIAGNOSIS
I JH0028-70MI* I Figure 36 Manual Third

HYDRAULIC DIAGNOSIS 70044-39
MANUAL THIRD
CONVERTER CLUTCH - RELEASED
FORWARD CLUTCH - APPLIED
OVERRUN CLUTCH - APPUED
3.4 CLUfeH - APPLIEP
A forced 4-3 downshift can be accomplished by moving the selector lever from Drive 10) Range to
Third {3rd) Gear. When the selector lever is moved to the Third (3rd) Gear position, 03 oil from the
manual
valve is directed to the following:
1. 4-3 Sequence Valve
2. Part Throttle and Drive 3 103) Checkball 131
3. 3-4 Shift Valve
03 oil will close the 34 shift valve and allow the 4th signal oil to exhaust.
D3 oil combined with the 4-3 sequence valve spring force will close the 4-3 sequence valve to allow
the fourth and fourth accumulator oil to exhaust and release the band. 03 oil then flows into the over-
run clutch passage where it applies the overrun clutch to keep the forward sprag clutch from over-
running when engine braking is n~eded.
The forward and 3-4 CIU~C~~S are applied. The 2-4 band is released. The transmission is in Manual
Third,
direct driva The overrun clutch is appRad to allow engine braking.
*NON E,C.M, CONTROLLED VEHICLES
In manual 3td, the converter is shown released by the engine vacuum switch and there is no M.T.V.
up or M.T.V. down pressure, This is assuming the throttle is released. If the throttle is opened
sufficiently, the converter clutch could engage and the M.T.V. up and MXV. down valves coJd open.
JHOtOQ7WRI I
Figure 36 Manual Third

7004440 HYDRAUUC DfAGNOSIS .
MANUAL S-ECOND
-- I,.
,&-.-a- .I#,. s,,,,, iJ Fi~3;lilr
I JHJHI27+70QR4 I FIgure 37 Manual Second

, HYDRAULIC PlAGNQSlS 7004441
MANUAL SECOND
COWERTER CLUTCH - RELEASED
OVEARUN CLUTCH - APPLIED
2.4 MUD - APPLIED
I
FORWARD CLUTCH - APPLIED
I
A forced 3-2 downshift cen be a~cornplished by moving the selector lever from Third (3rd) Gear to
Second (2nd) Gear position.
When
the selector lever is moved to the Second (2nd) Gear position, RND4D3, 3rd clutch, and 3rd
accumulator oil
will exhaust at the manual valve, With no pressure to apply the 34 clutch, or release
the 2-4 band, the transmission will shift to second gear.
The manual valve will also direct line pressure into the D2 passage, Drive 2 (D2) oil will act on the
reverse boost valve to boost line pressure to 1206 kPa (I75 psi) which is required to prevent the 2-4
band and forward clutch from slipping.
SUMMARY
The forward clutch and 2-4 band are applied. The transmission is in second gear. Also, the werrun
clutch is still applied to allow engine braking when needed.
JHOlUWOOR4 1
Figure 38 Manual Se~ond

700.R442 HYDRAULIC DIAGNOSIS
I 1
MANUAL U)
J JHOOPSPOR4 I Figure 39 Manual Lo

MANUAL LO
CONVERTEM CLUTCH - RELEASED
FORWARD CLUTCH - APPLIED
Maximum downhill braking can be obtained at speeds below 30 mph (48 kmlh) with the selector
in Lo (tat) range. Lollst oil pressure, which is 1206 kR I175 psi), is the same as second (2nd) oil pressure
because second (02) oil is still present.
Lo oil from the manual valve is directed to the following:
1* 1-2 Shift Valvelain
2. to and Reverse Clutch
3. Lo Overrun Valve
Lo oil at the 1-2 T.V. valve combined with the 1-2 throttle valve spring force will close the 1-2 shift
valve at speeds approximately 36 mph 156 km/h) or below. This allows 2nd oil to exhaust, releasing
the 2-4 band, and lo oil to apply the lo and reverse clutch.
Loflst oil coming off the 1-2 T.V* valve is directed toward the lo overrun valve that regulates lolreverse
oil. This smoothes the 2-1 manual downshift for maximum engine braking.
The forward clutch is applied. The lo and reverse, and the overrun clutch are applied to allow engine
braking.
The 2-4 band is released, the transmission is in Lo Range - First Gear.
HYDRAULIC DIAGNOSIS 700-RU3
OVEARUM CLUTCH - APPLIED
LO ROLLER CLUTCH - APPLIED
JH018&7WR4
Figure 40 Manual Lo