Occasionally, a transmission slips out of gear
because the driver does not fully engage the gear when
moving the lever. However, when a transmission slips
out of gear fairly often, it should be replaced.
OVERHAUL OF THE TRANSMISSION
Because of the variations in construction of
transmissions, different procedures in the removal,
disassembly, repair, assembly, and installation must be
followed. These operations generally require from 5 to
7 hours, depending on the procedure followed. If you
are working on a vehicle with which you are not familiar,
always check the manufacturers manual.
Before removing the transmission from the vehicle,
make sure all accumulations of dirt or road mud are
cleaned from the case and the attached parts. Note or
mark by scratching the case with a sharp pointed tool,
any moist oil spots or unusually heavy accumulations of
oil-soaked road mud; these we good clues to the location
of small cracks or holes that might escape notice in
visual inspection. However, do not confuse these
accumulations with those that result from leaking
gaskets or oil seals. A leak at a gasket or a seal is more
or less normal on a transmission that has been in service
for any length of time.
Drain the lubricant from the transmission. Some
manufacturers recommend flushing the transmission
before removal. This is done by filling the transmission
with a flushing oil and operating the engine with the
transmission in neutral for several seconds. After this,
drain the flushing oil from the transmission.
After removing the transmission case, complete the
external cleaning operation with steam-cleaning
equipment or by hand brushing the case, using an
approved cleaning solvent.
After the transmission is disassembled, make sure
all parts are cleaned thoroughly and individually.
Clean away all the parts of hardened oil, lacquer
deposits, and dirt, paying particular attention to the
small oil holes in the gears and to the lock ball bores in
the shifter shaft housing. Remove all gaskets or parts of
gaskets using a scraper or other suitable tool. Make sure
the metal gasket surfaces are not gouged or scratched.
After all parts of the transmission have been
thoroughly cleaned, inspect them to determine whether
they can be reused or scrapped. The wear or damage to
some of the parts will be evident to the eye, (fig. 11-8)
whereas, in others, it may be necessary to use tools or
gauges to determine their condition. Since the decision
as to whether apart should be scrapped or reused is often
a matter of opinion or judgment, you may want to do
this job yourself. If you can not do the inspecting
yourself, make sure the person doing it is experienced
in transmission maintenance and overhaul.
When inspecting transmission parts, bear in mind
that the inspection procedure has two objectives; first,
to eliminate any part or parts that are unsuitable for use,
or doubtful parts that may cause the premature failure
of the overhauled transmission; second, and equally
important, to reduce the wasteful practice of scrapping
parts that still retain a high percentage of useful life.
Figure 11-8.An example of worn external teeth of a synchronizer clutch.