Pontiac Fiero 1988 Service Manual page 768

HYDRAULIC DIAGNOSIS 125C-27
PART THROTTLE 3-2 DOWNSHIFT
(Valves In S e c o n d Gear Position)
CONVERTER CLUTCH - RELEASED
FORWARD CLUTCH - APPLIED INTERMEDIATE BAND - APPLIED
A part throttle 3-2 downshift can be accomplished below approximately 5 0 mph (80 km/h) by
depressing the accelerator pedal far enough to move the throttle valve (T.V.) plunger to allow shift
T.V. oil to enter the part throttle (P.T.) passage. This oil, called part throttle (P.T.) oil, is then routed
to the 2-3 T.V. valve.
Part throttle oil and the 2-3 spring force will close the 2-3 shift valve against governor oil, shutting
off RND oil to the direct clutch passage. Exhausting direct clutch oil opens the 3rd clutch pressure
switch releasing the torque converter clutch, seats the direct clutch exhaust checkball (1), flows through
the t w o orifices, and is exhausted at the 2-3 shift valve. A t the same time, direct clutch accumulator
oil from the intermediate servo also exhausts through the same route as directed clutch oil. Second
oil acting on the servo piston applies the band for a smooth band apply as the direct clutch
is released.
J H 0 0 2 4 - 1 2 5 C
Figure 24 Part Throttle 3-2 Downshift - Valves in Second Gear Position