TM-9-2350-311-20-2
HOWITZER, MEDIUM, SELF-PROPELLED, 155MM; M109A2, M109A3, M109A4 AND M109A5
TECHNICAL MANUAL; UNIT MAINTENANCE MANUAL FOR CAB, ARMAMENT, SIGHTING AND FIRE CONTROL, ELEVATING AND TRAVERSING SYSTEMS AND ASSOCIATED COMPONENTS
DECEMBER 1993
TM-9-2350-311-20-2 - Page 48 of 828
TM 9–2350–311–20–2
1–17
1–15 DIFFERENCES BETWEEN MODELS
Most of the differences among components of M109A2 and M109A3 howitzers concern the M109A3 model. There are 103
differences in the cabs of the M109A3 vehicle population. Variations among M109A2 vehicles and differences between
M109A2 and M109A3 vehicles are minimal.
M109A4 howitzers have updated hydraulic and electrical components and an added NBC system. M109A5 howitzers
have been updated from the M109A4 models. In addition to all M109A4 updates, the M109A5 model also modifies the
M185 cannon assembly to an M284 cannon assembly and M178 mount to an M182 mount.
The maintenance procedures in this manual will call the mechanic’s attention to any differences in cab components which
will affect the mechanic’s performance of unit maintenance tasks. Where parts which must be removed or inspected differ
significantly in appearance, a cutaway view will be used to show the alternate parts.
Part differences not relevant to the unit mechanic will not be mentioned or
pictured.
Below are some examples of cab component
differences important to the unit
mechanic.
Functional group and part
Number of Variations
How assemblies/parts differ
00
Protective shields, race ring
3
Shields mount on race differently.
Some M109A3 howitzers do not
have a turret shield behind the com-
mander’s seat.
01
Bearing balls
2
Some vehicles have 212 bearing
balls mounted on 106 race ring
spacers; other vehicles have 213
bearing balls mounted on helical
compression springs.
02
Cannon assembly, howitzer
2
M109A2/M109A3/M109A4 howit-
zers have M185 cannon assembly
with M35 firing mechanism. M109A5
howitzers have M284 cannon as-
sembly with M49 firing mechanism.
Cannon assemblies are similar in
maintenance characteristics, but
there are subtle differences in parts.
Refer to TM 9–2350–311–24P–2 for
specific part number changes.
Carrier assembly on M284 cannon
assembly has a spring-loaded plunger
assembly. The plunger assembly on
the M185 cannon assembly is not
spring-loaded.
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