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Hook-up on trailer safety chain hooks.






Dear Editor,

Would you please tell your readers riot to bend the hooks on trailer safety chains to fit the shackles on the back of FMTVs? You told us on Pages 11-13 of PS 673 about NSNs For larger hooks and extensions For the chains. That should've been enough to stop people from bending open hooks, but we're still seeing this in the field.

Robert L. Matson



Fort Hood, TX

Editor's Note: Can do, Sir. To give you a little history, the FMTV manufacturer increased the size of the FMTV's tow shackles to meet new air transport and rail tie-down requirements. When this happened, the tow shackles fit the size and weight of the FMTV trailer, but not the smaller hook size of the lunette trailers that must be towed.

Instead of bending open hooks, follow these steps to ensure the trailer safely chains are the right fit:

1. Remove the current hook and connecting link from the forward end of the trailer safety chains.

2. Couple the trailer to the FMTV at a 45-degree angle.

3. Attach the new safety chain hook to the FMTV tow shackle opposite the trailer angle.

4. Cross the safety chain under the trailer tongue. Then pull the end of the chain and eye or clevis end of the new hook toward each other.

5. Measure the distance between the eye or clevis of the hook and the end of the safety chain. Add the length of one more chain link. That will be the cut length for the extension chain.

6. The connecting link joining the 3/8-in extended chain to the original 3/8-in chain will add the correct amount of slack to the safety chain without its being too long or too short.

Alternate 3/8-in connecting link, NSN 4010-01-379-0918

Hook, NSN 4030-01-501-6946

Existing chain

Chain, NSN 4010-00-286-5645

3/8-in connecting link, NSN 4010-01-041-9751

Length of chain extension to be determined by user

And here are a few special reminders:

When attaching to a truck that has no extended pintle, you '11 need to shorten the trailer safety chains so they're not too long and drag or get caught on underbrush or commo wire. One way is to twist the chain several times to lake up the slack.

If you have an MI05A3, MI01A2 or -A3, or a lunette trailer with a surge brake device, you have to adjust the length of the breakaway cable/chain. Make it a bit shorter than the safety chains. Then if the trailer disconnects from the low pintle, the breakaway cable/chain will fully actuate the trailer brakes before the slack in the safety chains is taken up.

Consider this the latest and greatest guidance on this issue.

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Title Annotation:FMTVs and Lunette Trailers ...
Author:Matson, Robert L.
Publication:PS, the Preventive Maintenance Monthly
Geographic Code:1USA
Date:Dec 1, 2012
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