why do nuts stay tight on spring hanger bolts?

[mike_c]

Hi all--

Work on my chassis is progressing! The frame and cross members are done, I'm welding on the tongue today, and I've mounted the axle sort of. I say "sort of" because I have the axle seat and the front and rear spring hangers welded on and the axle bolted up loosely, but nothing is tightened yet.

I'm using an Alko 2K# straight axle, mounted underslung.

Looking at it is sketching me out though. First, the U-bolt nuts came without lock washers and I wonder how tight they'll stay. Can anyone offer some reassurance about that, or should I go and buy lock washers anyway?

Second, I realize now how the springs flex in the rear hanger and shackle, and I'm freaked out about the nuts loosening as the bolts rotate slightly in the hanger and shackles. What keeps them from loosening?! The bolts are splined, so I can see how they move "with" the shackles, but what about the nuts? Why don't they loosen as the shackle moves back and forth and the bolts twist slightly in response?

--Mike C.

[LDK]

Maybe you could use lock washers and nylock nuts too. Just a thought.

[Cdash]

I am by no means and expert, but when I had to replace these on my rather large RV with tandem axles, the bolts were shouldered, and only threaded on the end. So there was really no outward pressure on the nut that would cause the rotation to loosen it.

[mike_c]

I am by no means and expert, but when I had to replace these on my rather large RV with tandem axles, the bolts were shouldered, and only threaded on the end. So there was really no outward pressure on the nut that would cause the rotation to loosen it.

I'm guessing that's the case with mine, too, although the shoulder is certainly not obvious-- but the threads are only cut on the ends of the bolts and I'm assuming that once the splines are fully seated there won't be any contact with the nuts, even when they're tightened all the way down, because they'll be at the end of the thread and still have some air between them and the shackles, etc. Scares me to look at it assembled loosely and think about pulling it down the highway with the shackles flexing back and forth, though!

--Mike C.

[Steve_Cox]

Most hangar bolts use distorted thread locking nuts. Photo came from Mcmaster.com is of a center distorted thread, but there are several types including an oval distortion that is almost undetectable just looking at it.

[Yota Bill]

as Steve Cox said, the nuts should be a design that is self locking, and some of the designs take a very close look to see the distortion. I always leave mine with a small gap to make sure the spring and shackles do not bind. You dont want to crnk those down tight so that the spring or shackles cannot turn around the bolt.
If you think they are not self locking, or are still concerned with it, thread another nut on and tighten it against the first one (if you have enough threads), which will stretch the bolt slightly between the two nuts and lock them both in place, and still allow you to leave a small gap.

[dh]

Most hangar bolts use distorted thread locking nuts. Photo came from Mcmaster.com is of a center distorted thread, but there are several types including an oval distortion that is almost undetectable just looking at it.

+1

[Dale M.]

Most hangar bolts use distorted thread locking nuts. Photo came from Mcmaster.com is of a center distorted thread, but there are several types including an oval distortion that is almost undetectable just looking at it.

Ditto....

Dale

[mike_c]

Today it gets a tongue and (hopefully) stabilizer jacks!

--Mike C.

[dh]

These distorted thread bolts go on like nylocks. A little trick I use to make life easier when putting all 6 in a trailer is to use an air ratchet (not impact gun) which goes slow enough that you won't overtighten.

[grant whipp]

Most hangar bolts use distorted thread locking nuts. Photo came from Mcmaster.com is of a center distorted thread, but there are several types including an oval distortion that is almost undetectable just looking at it.

+2 ...