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TM 9-2520-249-34&P
(1) A 27-tooth, spiral bevel drive gear (44)
However, these two elements are rotating at different
is supported on roller bearing assembly (36), mounted
speeds. As a result, the low-range carrier is driven at a
on the hub of support (38), and roller bearing assembly
third rate of speed.  The drive ratio between the
(35), mounted on the hub of carrier (32). These parts
converter output shaft and bevel drive gear in this range
are assembled as a unit and installed in the front of
is 2.246 to 1.
bevel gear housing (9) Shims (37) control the preload on
(3) Notice that, although the speed is
the bearings, and shims (28) control the axial positioning
reduced in the intermediate-range planetary, it is
of bevel drive gear (44).
modified by the low-range planetary before it reaches
(2) The bevel driven gear is press-fit to its
the bevel drive gear.  This interaction between two
cross shaft, positioned by a snap ring and held in place
planetary gear sets is called compounding.
The
by spacer (45, FO-5) and spanner nut (47) Roller
intermediate-range operation is the only instance in
bearing assembly (40), mounted in right bearing retainer
which compounding is used in the XTG 250-1A
assembly (1), supports the bevel driven gear and right
transmission.
end of the cross shaft. Roller bearing assembly (46),
mounted in left bearing retainer assembly (20), supports
2-9.
Low-Range Planetary Gearing.
the left end of the cross shaft. Shims (7 and 19) control
a.  Description (FO-4).
the preload of roller bearing assemblies (40 and 46) and
(1) Planetary  gearing  for  low  range
position bevel driven gear and shaft assembly (43) in
includes three main elements-sun gear, ring gear, and
relation to bevel drive gear (44).
carrier assembly. An 8-pitch, 22-tooth sun gear (19),
b.  Operation (FO-5). The bevel drive gears
integral with the intermediate-range sun gear, is splined
transfer torque from the forward-range gearing, which is
to the converter turbine shaft and is the driving element.
in line with the engine crankshaft, to the cross shaft and
An 8-pitch, 70-tooth (internal teeth) spur gear (44) with
thus to the right and left output sections. The speed
external splines is the reaction member.  Planetary
reduction ratio from bevel drive gear (44) to bevel
carrier (52) contains four, 8-pitch, 24-tooth pinions (51.5)
driven gear and shaft assembly (43) is 1.444 to 1. The
mounted on four spindles (51.1) which rotate on bearing
bevel driven gear also drives the brake coolant pump
rollers (51.4).  The carrier is the driven element (2)
through the pump gear (42).
Spacers (51.3 and 51.6, FO-4) position bearing rollers.
Thrust washers (51.2 and 51.7) position the pinions and
2-11.
Reverse-Range Planetary Gearing, Left and
absorb the pinion end thrust forces. The spindles are
pressed into the carrier and locked in place by pins
Right
(51.8).  A splined hub at the rear of the carrier (52)
a.  Description (FO-6 and FO-9).
engages the internal splines in bevel drive gear (44,.
NOTE
b.  Operation (FO-4).
The right reverse-range planetary (FO-9) and
(1) When  the  low-range  clutch  is
the left reverse-range planetary (FO-6) are
engaged, spur gear (44) is prevented from rotating. Sun
identical.
Therefore, description of one
gear (19), being driven by the converter turbine shaft,
planetary will serve to describe the other.
rotates pinions (51.5) which mesh with spur gear (44).
The description below is keyed to foldout 6,
The rotating pinions then travel within the circumference
the left reverse-range planetary.
of the stationary spur gear. Thus, the torque imparted
by the sun gear to the pinions is transmitted to the
(1)
The reverse-range planetary gearing
carrier and causes it to rotate.
consists mainly of three elements-sun gear, ring gear,
(2) Torque of the carrier is transferred to
and carrier assembly.  An 8-pitch, 32-tooth sun gear
bevel drive gear (44, FO-5). In addition to the primary
assembly (47, FO-6), (integral with the steer ring gear),
function of providing low-range speed reduction, the
is splined to the cross shaft and is the driving element.
low-range planetary also functions during intermediate-
A 67-tooth ring gear (integral with brake hub 45) is the
range operation as described in paragraph 2-8b(2 and
driven element.
3), above.  Speed reduction in low-range operation
(2)
Planetary  carrier  (24,  FO-6),  the
provides a drive ratio of 4.182 to 1 from the converter
reaction element, contains six, 17-tooth pinions (26.3)
shaft to the bevel drive gear.
which rotate on pinion rollers (26.4), placed between the
pinions and spindles (26.7). Spacers (26.2 and 26.5)
2-10.
Bevel Drive Gears and Cross Shaft
position pinion rollers (26.4).
a.  Description (FO-5)
2-4

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