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M939/A1/A2-series trucks ... tires, CV joints & seals.

Unnecessary tire wear on M939-series 5-tonners in the "sandbox" has more than a few mechanics scratching their heads.

They've checked the CTIS and tire pressure, and it's on the money. The front wheels disengage when the Front Wheel Drive Selector lever is moved to the OUT position.

And even after taking the truck in for a front end alignment, excessive tire wear is still a problem. What gives'?

It could be the truck's Carden-style CV joints are worn. They can cause premature tire wear, especially on older trucks.

To prevent that tire wear, you mechanics can put in more durable CV joints on both front drive shafts. NSN 2520-00-734-6985 gets the left side CV joint. NSN 2520-00-734-6984 gets the right side joint. The replacement CV joint is rubber-encased.

Axle Seals

There are two different seal assemblies for the M939A2-series truck's front axle. Which seal is used depends on the CV joint.

The shaft diameter on the CV joints is different. That's why different seals are found on the same model trucks.

By the way, you don't need the thrust washer, item 9 shown on Page 3-426 of TM 9-2320-272-24-1 with the new CV joint.

HERE'S THE LOWDOWN YOU NEED TO REMEMBER UNTIL THIS INFO IS ADDED TO THE TMS ...

* Seal assembly, NSN 4320-00-734-6951, is used on M939A2-series trucks with the newer rubber-encased CV joint. This same seal is also used on M939 and M939A1 trucks.

* Seal assembly, NSN 5330-01-271-9490, is used on all M939-series trucks with the original Carden-style CV joints.

* Seal, NSN 5330-01-271-9362, is used on M939A2-series trucks with the original Carden-style CV joint.

* Use the NSNs shown in Fig 236 of TM 9-2320-272-24P-1 for all other M939-series trucks.

[ILLUSTRATIONS OMITTED]
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Title Annotation:Wheeled Vehicles
Publication:PS, the Preventive Maintenance Monthly
Article Type:Brief Article
Geographic Code:1USA
Date:Mar 1, 2005
Words:282
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