First, in some models it is easier and faster to
typical hydraulic control unit (valve body) is shown in
remove the engine and transmission as one unit. After
t h e e n g i n e a n d t r a n s m i s s i o n a r e r e m ove d , t h e
Other hydraulic system components such as
transmission can be disconnected from the engine.
pumps, lockup clutches, retarders, high-low splitters,
governors, and oil pressure regulator valves, if separate
Prior to removing the transmission, it should be
from the unit, are disassembled, cleaned, inspected,
drained of fluid, all lines disconnected and plugged, all
a n d r e p a i r e d i n a ve r y s i m i l a r m a n n e r t o t h e
linkages disconnected, and all electrical wires
components of the hydraulic control unit.
disconnected, if required. The drive shaft must be
removed, and the tail shaft plugged or bagged and
Before reassembly of the control unit, all parts
taped to prevent fluid from spilling as the unit is
should be cleaned with the proper solvent and blown
d r y w i t h c l e a n , m o i s t u r e - f r e e , l ow - p r e s s u r e
compressed air. If compressed air is not available, the
Automatic transmissions are very heavy. Many
parts should be drip-dried. You should NEVER wipe
models weigh over 200 pounds, so you must have the
the parts with any type of material that may leave lint.
proper sling or transmission jack to raise or lower the
Table 2-1 is a troubleshooting chart that lists many
of the typical problems that occur with automatic
Upon installation, make sure that all mounting
transmissions. The table also includes probable causes
brackets are in place, and that hardware is secured prior
for the problems and suggested remedies. The intent is
to removing the supporting unit (sling or jack). Then,
always to try to solve the problem before tearing down
reconnect the lines, wires, linkage, and drive shafts
the unit for repair or replacing it.
according to the technical manual for the transmission.
Service Diagnosis and Repair of Automatic
The procedures for removal and replacement of
The transmission should not be removed nor
transmissions vary depending on the model that you
disassembled until a careful diagnosis is made, the
are dealing with. Therefore, an in-depth discussion
definite cause determined, and all possible external
will not be provided here, just a few things that are
corrections performed. In diagnosing any abnormal
common to all transmissions.
FRONT PUMP CHECK VALVE
ONE LARGE STEEL BALL
Figure 2-80.--Typical hydraulic control unit.