Reverse . Engine Idling; Transmission Fluid - Pontiac FIREBIRD 1972 Service Manual

7G-30 1972 PONTIAC SERVICE M A N U A L
DRIVE RANGE
-
PART THROTTLE DOWNSHIFT allow modulator oil to enter the 3-2 part throttle passage.
If the modulator pressure in the 3-2 part throttle oil pas-
A 3-2 part throttle downshift can be made below approxi- sage, plus the 2-3 shift valve spring, is sufficient to move
mately 42 m.p.h. At a light throttle opening, the 3-2 part the 2-3 shift valve against governor pressure to its down-
throttle oil passage is exhausted, however, at a moderate
shifted position, the transmission will be in second gear.
throttle opening, the detent valve is moved enough to
R E V E R S E
-
E N G I N E I D L I N G
POWER FLOW
1. Direct Clutch.
2. Low and Reverse Clutch
Intermediate Clutch
................................................
Off
Direct Clutch
...........................................................
On
Forward Clutch
........................................................
Off
Low and Reverse Clutch
........................................
On
Intermediate Overrun Roller
Clutch
..................................................
Free Wheeling
Low and Reverse Roller Clutch
............
Free Wheeling
Intermediate Overrun Band
..................
Off
OIL FLOW
When the range selector lever is moved to the reverse (R)
range position, the manual valve is repositioned to allow
line oil pressure to enter the reverse oil circuit. Reverse oil
then is directed to:
3. 1-2 Shift Control Valve.
4. 2-3 Shift Valve.
5. Reverse Boost Valve.
Reverse oil from the manual valve flows to the outer area
of the direct clutch piston, to the outer area of the low and
reverse clutch piston, to the 1-2 shift control valve and to
the 2-3 shift piston. Reverse oil comes out of the 1-2 shift
control valve as low or reverse oil and is directed to the
inner area of the low and reverse piston. Reverse oil at the
2-3'shift valve is regulated to 2-3 clutch oil and applies the
direct clutch. Reverse oil also acts on the reverse boost
valve to increase the line oil pressure to a maximum of 250
p.s.i. at stall.
S U M M A R Y
The direct clutch and the low and reverse clutch are applied, line pressure
is boosted and the transmission is in reverse gear.
PERIODIC SERVICE RECOMMENDATIONS
T O W I N G
If the transmission, drive line or axle do not have a mal-
function, the vehicle may be towed in neutral, with steer-
ing column unlocked, at speeds up to 35 mph. The
distance should not exceed 50 miles.
For higher speeds or extended distances, it is recom-
mended that the propeller shaft be disconnected or the
rear wheels be off the ground.
TRANSMISSION FLUID
Transmission fluid level should be checked (with trans-
mission hot) every time engine oil level is checked or every
6,000 miles when engine oil is changed.
CAUTION:
Since the Turbo Hydra-Matic
(M-38) transmission is very sensitive to oil
level, special precautions should be taken when
checking the oil level to ensure against an over-
fill
(see Checking Procedure, under MINOR
SER VICE).
Transmission fluid should be changed and the strainer
cleaned every 24,000 miles or 24 months. When the car is
in heavy duty service (police, taxi, fleet service or for cars
subjected to heavy city traffic during hot weather), it is
recommended that the fluid be changed and the strainer
cleaned at 12,000 mile intervals.