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 TM 9-8000
(1) Neutral When the gearshift lever is
(c) Because the sungear is locked, it
placed in neutral, the clutch and brake bands are
acts as a reactionary member. This causes the
released. The input shaft rotates freely and no torque is
planetary pinions to walk around it and rotate the front
transmitted to the output shaft.
planetary carrier, which drives the attached output shaft.
(2) Drive-Low. When the gearshift lever is
(4) Direct Drive. When the gearshift lever
placed in drive, the automatic transmission will be in low
is in drive and vehicle speed is above approximately 25
gear when the vehicle is in a speed range of zero to
miles per hour, the automatic transmission normally is in
approximately eight miles per hour. In drive-low the rear
direct drive. In direct drive, both the front and rear
clutch is engaged, locking the input shaft to the internal
clutches are applied, which ultimately results in the
gear of the front planetary gearset. Power flow through
locking of the internal gear to the internal gear in the
the drive train is as follows:
front planetary gearset. This results in the planetary
gears being locked and the whole planetary gearset and
(a) From the input shaft to the internal
the attached output shaft rotating at a 1:1 speed ratio
gear of the front planetary gearset.
with the input shaft.
(b) From the internal gear to the
(5) Low. When the gearshift lever is
pinions of the front planetary gearset.
placed low, the power flow through the drive train is
identical to that of drive-low described above. The only
(c) Because the front planetary carrier
difference is the use of the rear brake band rather than
the overrunning clutch to lock the carrier of the rear
is locked to the output shaft, it cannot rotate
planetary gearset. Because the rear brake band
backwards and therefore acts as a reactionary member.
prevents the element from rotating in either direction, the
This causes the planetary pinions to drive the sun gear.
drive train is able to provide engine braking during
(d) The sun gear, which is common to
vehicle deceleration with the transmission in low. This
contrasts with drive-low, which allows the vehicle to
both planetary gearsets, then drives the rear planetary
freewheel during deceleration due to the one-way locking
pinions.
of the overrunning clutch.
(e) The rear planetary carrier, which
(6) Reverse. When the gearshift lever is in
is locked to the transmission case by the over- running
reverse, the front clutch is applied, locking the sun gear
clutch, serves as a reactionary member. The rear
planetary pinions, therefore, drive the rear planetary
to the input shaft. The rear brake band also is applied,
internal gear and the attached output shaft at a speed
holding the carrier of the rear planetary gearset
stationary. Power flow through the drive train is as
reduction ratio of approximately 2.45:1.
follows:
(3) Drive-Second. When the gearshift
(a)..From the input shaft to the sun
lever is in drive and the vehicle is between approximately
8 to 20 miles per hour, the transmission normally will be
gear.
in second gear. In second gear the rear clutch is
(b) From the sun gear to the rear
applied, locking the input shaft to the internal gear of the
front planetary gearset. The front brake band also is
planetary pinions.
(c) Because the rear planetary carrier
engaged, locking the sun gear stationary. Power flow
through the drive train is as follows:
is held stationary, it acts as a reactionary member. The
rear planetary pinions, therefore, drive the internal gear
(a) From the input shaft to the internal
of the rear planetary gearset and the attached output
gear of the front planetary gearset.
shaft in reverse rotation to the input shaft at a speed
reduction ratio of approximately 2.2:1.
(b) From the internal gear to the
pinions of the front planetary gearset.
23-11
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