The exploded views of subassemblies incorporated here
are for the mechanics convenience. The parts are
arranged in their correct order and may be used as a
reference for the assembly or disassembly of this unit.
The purpose of a synchronized transmission is to
simplify shifting and to help the driver get a clash free
shift. To receive these results, however, It is important to
under- stand how the synchronizer works.
When a shift is required, the operator declutches and
moves the shift lever toward the desired gear. When the
synchronizer ring makes contact with the gear, the
blockers automatically prevent the shift collar from
completing the shift until the gear and mainshaft speeds
are matched. At that time, the blocker automatically
neutralizes. The lever moves smoothly and easily into
It takes one or two seconds to match speeds. Steady
pressure on the shift lever helps the synchronizer do its
job quickly If the lever is "forced" into gear, it is possible
to override a blocker. This defeats the purpose of the
synchronizer, however, and can cause gear clash.
synchronized in first and reverse gears because these
gears are normally selected when the vehicle is
stationary. No synchronizing of engine speed and road
speed is required to get in gear from a stop.
Always start in first gear. Starting in any
other gear may cause hard shifting and internal
synchronizer needs gear rotation to do its job.
To begin shifting, first depress the clutch and wait for
complete release. Move the shift lever into 1 st gear.
Next, accelerate to an RPM that will allow enough
momentum to select the next higher gear while still
allowing vehicle acceleration after the shift has been
completed. (There is usually no reason to go all the way
to the governor before you shift to second.)The
progressive shift technique helps save fuel. This method
can vary depending on the GVW of the vehicle, road
condition and type of service.
When 2nd gear is desired. declutch and move the lever
toward 2nd, keeping steady pressure on the lever The
synchronizer will pick up the gear and synchronize its
speed to the mainshaft speed. The lever will move into
Continue in the same manner to top road speed. Notice
that to have good performance as you approach top road
speed, you must accelerate closer to the governed
speed before you allow the engine to drop to the next
gear shift point. This is because air resistance at higher
speeds requires more horsepower. You receive
maximum horsepower and performance at governed
However, the engine must be raised to the governor as
the clutch is engaged after completing the shift. To
downshift from top gear, declutch as you approach the
shift point (the shift usually starts about 100 RPM over
the shift point), and move the shift lever with a steady
even pressure toward 4th gear. The synchronizer will
pick up 4th gear and speed it up to vehicle speed,
allowing a clash free shift. After the shift, re-engage the
clutch while accelerating to keep the vehicle moving at
the desired speed. If further downshifts are required,
continue in the same manner.
When downshifting, remember that 1 st gear is not
synchronized. Double clutching is required to complete a
clash free shift. You can double clutch on all other shifts
as well. This only aids the synchronizer in doing Its lob
by manually helping to match the engine speed and road
Do not tow vehicles equipped with
Spicer transmissions without first pulling the axle
shafts or disconnecting the driveshaft. Lubrication
of the internal gear train is inadequate when the
vehicle is towed. Also, do not pull or roll start
vehicles in first or reverse gears.