PS Magazine - TB 43-PS-693
PS, The Preventative Maintenance Monthly
ISSUE 693
AUGUST 2010
11
PS 693
AUG 10
10
PS 693
AUG 10
N
owadays, people want things quick, fast, and in a hurry. But no one wants rapid
tire wear on their M939-series 5-ton trucks.
Premature tire wear shouldn’t be a problem
IF:
•
your -A2 truck’s CTIS maintains the right tire pressure
•
the front wheels disengage when the front wheel drive selector lever is moved to
the OUT position
•
you have a functioning linear valve that engages and disengages 6-wheel drive
•
the front end is aligned
But if premature tire wear is still a problem, you may be able to slow it down by
giving some attention to your truck’s Cardan and CV joint’s front internal axles. If
the Cardan and CV joints are worn, they can cause premature tire wear, especially
on older trucks. Get your mechanic to replace the Cardan and CV joint internal axles
when necessary.
You may Fnd different combinations of internal front axle shafts on the M939
±OV due to unscheduled maintenance. Determine which joints need replacing on
these trucks. You can Fgure out which internal front axle to remove and replace by
measuring the outside diameter of the seal surface of the axle.
±or M939A2s, if the outside diameter measures approximately 2.44 inches (and
no less), your truck has the Cardan joint internal axle, also known as the U-joint style
internal axle.
The M939A2-series truck’s front internal axles have Cardan joint axle left hand
shafts, NSN 2529-01-271-8024, and right hand shafts, NSN 2520-01-271-8025. To
replace the seal retainer assembly, order retainer assembly, NSN 5330-01-271-9490.
The seal that’s used with the retainer assembly is NSN 5330-01-271-9362.
Note: If you want to change just the seal itself, you’ll need a special tool that’s
called out in the TM for that procedure. If that tool’s not available, the truck headshed
recommends that you just order the retainer assembly.
±or M939s and M939A1s, if the outside diameter on the same seal surface area
measures about 2.122 inches (and no less), your truck has Cardan joint internal axles.
Order replacement shafts for M939 and M939A1 truck front axles equipped with
Cardan joint axle shafts using NSNs 2520-00-734-6985 (left-hand) and 2520-00-
734-6984 (right-hand).
By the way, these NSNs will bring
you CV joint internal front axles with
the same seal surface outside diameter
measuring 2.122 inches. They are a
suitable
replacement
internal
axle.
Cardan internal axles measuring 2.122
inches have been discontinued, so you
can’t order them.
You can replace the seal retainer
assembly using NSN 4320-00-734-
6951. The seal itself that’s used in this
retainer assembly comes with NSN
5330-00-145-8355. You can change
this seal using common tools.
Note that the measurements of the internal axle seal surface outside diameters
mentioned are the only possible measurements you can have with the Cardan joint/
U-joint style internal axles.
M939, M939A1, and M939A2 front axles equipped with constant velocity (CV)
internal axle shafts, NSN 2520-00-734-6985 (left hand) and NSN 2520-00-734-6984
(right hand), use retainer assembly, NSN 4320-00-734-6951.
The seal used in this retainer assembly is NSN 5330-00-145-8355. This seal can
be changed using common tools.
Slow
Down
Tire
Wear
M939/A1/A2-Series Trucks…
Slow
Down
Tire
Wear
I’ve checked
everything on
this truck…
I’m a cv joint and I’m
tougher than you are,
cardan joint!
…
what
is
causing all this
tire wear!?
yeah, but I’m
still usable!
so there!
N
693.10-11.indd
1-2
7/2/10
5:25:24 PM
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