Copyright © 1996 General Motors Corp. 2–1
2–1. SCOPE
This section describes and explains the operation of
the components and systems of AT transmissions.
Where features are common to all models, no refer-
ence will be made to models. Where features are pecu-
liar to a model, the model will be noted.
2–2. MOUNTING
a. To Engine.
The front of the transmission
housing is an SAE size 3 flange. This flange is bolted
to the rear of the engine.
b. To Vehicle.
Two
5
⁄
8
-11 tapped holes at each
side of the transmission are provided for mounting to
supports in the vehicle.
2–3. INPUT DRIVE
a.
For models other than AT 543, six tapped lugs
are on the front of torque converter 1 (Foldout 7,B) for
attachment of a flexible disk drive. The outer bolt cir-
cle of the disk drive is bolted to the lugs. The inner
bolt circle is bolted to the engine crankshaft or crank-
shaft adapter hub.
b.
For AT 543 models, six threaded studs are on
the front of torque converter 2 (Foldout 7,A) for the at-
tachment of a flexible disk drive using nuts 1.
2–4. TRANSMISSION HOUSING
Transmission housing assembly 6 (Foldout 12,A) is
cast aluminum. It houses the clutches and gearing, oil
pump, governor, main control valve, and oil pan. A
parking brake mounting surface is provided at the rear.
On the right side is a provision for a power takeoff or
for the retarder control valve, depending upon the type
of model.
2–5. TORQUE CONVERTER ASSEMBLY
AND LOCKUP CLUTCH
a. Description
(1) AT 500 Series transmissions have torque
converters that include a pump, a turbine, and a stator.
The pump is driven by the engine. The turbine drives
the turbine shaft. The stator is mounted on a freewheel
clutch, the hub of which is splined to a stationary
ground sleeve. The hub of the torque converter pump
drives the transmission input pressure pump.
(2) AT 1500 Series transmissions are
equipped with an automotive-style lockup torque con-
verter. In addition to the pump, stator, and turbine as-
semblies, a lockup clutch and damper assembly is
incorporated. A lockup valve, located in the front sup-
port assembly, controls flow through the torque con-
verter and provides operation in third and fourth
ranges.
(3) AT 540, 542, 545, 1542, or 1545 Series
torque converter 1 (Foldout 7,B) is a closed, welded
unit that cannot be disassembled.
(4) AT 543 torque converter 2 (Foldout 7,A)
is a serviceable assembly.
b. Operation
(Foldout 1, 2, or 3)
(1) The torque converter assembly is contin-
uously filled with transmission fluid, which flows
through the converter to cool and lubricate it. When
the converter is driven by the engine, the pump vanes
throw the fluid against the turbine vanes. The impact
of the fluid against the turbine vanes tends to rotate the
turbine.
(2) The turbine, splined to the turbine shaft,
transmits torque to the transmission gearing. At engine
idle speed, the impact of fluid against the turbine vanes
is minimal. At high engine speed the impact of the
fluid is much greater on the turbine, and high torque is
produced.
(3) Fluid thrown into the turbine flows to the
stator vanes. The stator vanes change the direction of
the hydraulic flow (when the stator is locked against ro-
tation), and directs the fluid to the pump in a direction
that assists the rotation of the pump. It is the redirection
of the fluid by the stator that enables the torque con-
verter to multiply input torque.
(4) Greatest torque multiplication occurs
when the turbine is stalled and the pump is rotating at
its highest speed. Torque multiplication decreases as
the turbine rotates and approaches the speed of the
pump.
(5) When turbine speed approaches the
speed of the pump, fluid flowing to the stator begins
striking the backs of the stator vanes. This rotates the
Section 2 – DESCRIPTION AND OPERATION
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