Copyright by Goodheart-Willcox Co., Inc.
198 Automatic Transmissions and Transaxles
7
8
9
6
5
4
3
14
2
1
11
10
12
13
1. #12 Check ball
2. Plug, cup (orifice)
3. Valve, abuse
4. Spring, abuse valve
5. Stop, abuse valve
6. Pin, spring
7. Valve, low overrun clutch
8. Spring, low overrun clutch valve
9. Pin, spring valve retaining
10. Piston, accumulator
11. Ring, oil seal accumulator piston
12. Spring, accumulator piston
13. Cover, auxiliary accumulator valve
14. Auxiliary accumulator valve body assembly
Figure 9-17. Accumulators are used to cushion the application of multiple-disc clutches and bands. The accumulator shown here is
contained in a separate, or auxiliary, valve body. (General Motors)
Detent valves are necessary since changes in throttle
pressure are not great enough to cause a downshift at high-
way speeds. The valve hastens the downshift, placing the
vehicle in a lower gear before vehicle speed is slow enough
to cause sufficient drop in governor pressure.
Note that some hydraulic circuit designs do not have a
separate detent valve. In these designs, kickdown is
achieved through the throttle valve. If the throttle valve is
moved far enough, a detent oil passageway is uncovered
and this oil is then routed to the appropriate shift valves.
Check Valves
A common type of check valve in automatic transmissions
is the check ball. Check balls are one-way valves; they allow
fluid to flow in one direction only. These steel balls are installed
in chambers next to holes in the valve body spacer plate.
In operation, fluid flow in one direction will push the
check ball into the spacer plate hole, sealing it. Fluid flow
in the opposite direction will push the ball out of the hole,
allowing fluid to flow.
Note that some transmissions use a spring-loaded
check ball. These may function to control torque converter
pressure, or they may serve in overpressure situations as
pressure relief valves.
Accumulators
An accumulator is a hydraulic device used in the apply
circuit of a band or clutch to cushion initial application. The
result is a smoother shift. The accumulator essentially con-
sists of a spring-loaded piston in a cylinder. The piston is
pushed to one end of the cylinder by the spring. A hydrau-
lic passageway connects the accumulator to the apply pis-
ton of a multiple-disc clutch or band servo.
As the clutch or servo is being applied, fluid in the
passageway is received by the accumulator. The accumula-
tor piston begins to move against spring pressure. The
expanding cylinder chamber diverts some of the hydraulic
fluid from the clutch or servo. As a result, pressure to the
clutch or servo does not build up to line pressure immedi-
ately, and the initial application of the holding members
will be soft. After the accumulator spring is fully com-
pressed, full pressure goes to the apply piston and the
clutch or band will be held tightly. Figure 9-17 shows a
typical accumulator installed in an auxiliary valve body.
Automatic Transmission Shift Linkage
The shift linkage is the only direct connection between
the driver and the automatic transmission. It makes a
mechanical connection between the driver and the trans-
mission hydraulic control system. The shift linkage consists
of a series of levers and linkage rods or cables. These transfer
motion to the manual valve in the transmission valve body.
Selector Lever
The shift selector lever in the vehicle’s passenger com-
partment can be mounted on the floor or on the steering
column. With either arrangement, movement of the selec-
tor lever causes the manual valve inside the transmission to
move. This action selects the driving range.