MWO-9-2320-272-35-1
MODIFICATION OF 5-TON M939, M939A1, M939A2 SERIES FAMILY OF VEHICLES (FOV)
M939 BRAKE STABILIZATION PROGRAM (RETROFIT OF ANTI-LOCK BRAKE SYSTEM (ABS) FOR M939 FOV); MODIFICATION WORK ORDER
JANUARY 2007
CHANGE 1
MWO-9-2320-272-35-1 - Page 13 of 109
MWO 9-2320-272-35-1
11
(5)
Verify operation of check valves by draining primary reservoir.
(a) Secondary reservoir pressure should NOT decrease as primary reservoir is being drained,
however a 10-15 psi decrease is allowable.
(b) If secondary reservoir pressure does decrease along with primary, inspect and clean or
replace the secondary reservoir one-way check valve as needed.
(6)
Verify air lines at brake treadle valve are properly connected at front axle limiting valve.
(a) Charge the air system to normal operating pressure (TM 9-2320-272-10).
(b) Disconnect the existing upper green tube at the front axle limiting valve.
(c) Have an assistant depress and hold down the brake pedal.
(d) Listen for escaping air at the green tube, and check the primary air gauge for decreasing
pressure.
(e) If secondary air gauge decreases, air line connections at the treadle valve are reversed and
should be properly connected (TM 9-2320-272-24).
b. Vehicle Preparation.
CAUTION
CAUTION
Install/route all air lines with sufficient length so that they do not
kink when permanently secured with wire ties. Install/route all
electrical wires so they are not subject to damage during vehicle
operation. Improperly installed/routed air lines may become
kinked and electrical lines may wear prematurely, or become
damaged, causing ABS system failure.
(1)
Park vehicle in a suitable work area, cage rear-rear axle brakes, and place vehicle on six jackstands
(M939) or two jackstands under rear-rear axle (M939A1/A2). (Refer to TM 9-2320-272-24.)
(2)
Drain air system. (Refer to TM 9-2320-272-10.)
(3)
Disconnect battery ground cables. (Refer to TM 9-2320-272-24.)
(4)
Remove rear-rear axle left and right wheels and tires (M939A1/A2). (Refer to TM 9-2320-272-24.)
WARNING
WARNING
Radial tires must be installed on all M939 basic models modified
with ABS. Failure to comply may result in injury to personnel.
(5)
Remove all wheels and tires (M939) from vehicle and replace tires with new radials.
(Refer to TM 9-2320-272-24.)
(6)
Remove rear-rear axle hub and drums. (Refer to TM 9-2320-272-24.)
(7)
Remove dustshield from hub (M939/A1). (Refer to TM 9-2320-272-24.)
(8)
Remove rear-rear axle brakeshoes. (Refer to TM 9-2320-272-24.)
NOTE
NOTE
Perform step 9 for exciter ring installation on M939/A1 vehicles
and step 10 for exciter ring installation on M939A2 vehicles.
Apply loctite 242 to threads of screws (M939/A1) at installation.
(9)
Clean mating surface area where dustshield was mounted on hub and install WHMB202010BC
exciter ring, five WWL5-16 lockwashers, and WSH5-16-18X050G8 screws as shown in figure 1.
Tighten screws 110-145 lb-in.
(10)
Press every other wheel stud (5 total) out of hub approximately 0.125-in. to 0.250-in. Clear
mating surface area around wheel studs and position WHMB202010BC exciter ring under
heads of five existing wheel studs and turn clockwise as shown in figure 2. Press wheel studs
down on exciter ring.
(11)
Drill a 0.625-in. hole in upper forward lobe of brake adjusting slot as shown in figure 3 using a
step drill or die grinder.
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