What’s this? (in a trailer’s suspension)
 

What is this arm called that carries the hub? What purpose does it serve?

(I am determined to know everything about my trailer ... and ... make it to the lake each and every trip out next year.)

That would be the torsion arm.

http://pi.b5z.net/i/u/1080235/i/Torflex-Image.jpg

The Torsion Axle, in my opinion, is the unwanted answer to a non-problem. I have seen more torsion axles fail on boat trailers than any leaf spring setup.

BTW, you shouldn't take my description of torsion axles as bad, many, many boat trailers, cars, buses, heavy trucks, etc... have been using this setup since the dawn of the automobile and they work fine. Actually in a trailer they might actually work better than a spring setup in some cases because the wheels work individually of each other. This cuts down on lots of rattling, binding, etc.. When you turn your tandem axle trailer the tires on the inside of the turn have to "scrub" or slide on the surface since they can not turn. On a torsion setup this is easier and causes less tire wear, in most cases.

However, lately, I have seen lots and lots of torsion bar failure on boat trailers. I think one major trailer manufacturer actually had a recall on their torsion axles. The axles usually use have a square tube with rod going through it that twists. The square tube is filled with a very hard rubber which compresses as the rod twists. This rubber tends to wear out and will eventually fall apart. The rubber usually wears faster due to sudden changes in heat. This is why it might not be ideal for use on a boat trailer, because when you get them wet they go through a temperature change very quickly.

Leaf spring suspensions on boat trailers also fail, but lately, not near as often.

To expand a bit more: instead of using a spring to support the suspension that application uses a keyed steel bar that twists to absorb load.

It is a similar set-up to what many 1/2 ton trucks use in the front suspension. It was also used in Porsche and VW suspensions for years. There really is no problem with a good torsion bar set-up, though I don't see much purpose for one on a boat trailer. I suppose one advantage would be setting the trailer crossbars lower to accomodate a lower boat position on the trailer.

Looks like Sam and I were typing at the same time.

Thanks fellas. Very smart.

Sam, see the Craftsman aluminum jack? I got that per your advice. Love it. I'm just looking for axles or things to lift and tires or parts to take off.

Do you see how rigid that suspension system looks side to side? One of the major "pros" of using a torsion axle setup is the side to side rigidity of the system in comparison to a leaf spring setup. In a leaf spring setup the trailer tends to have more side to side play and requires "trailer tires", with thick sidewalls to help stabilize the system. You often see "really cool" customized trailers with big wheels and low profile car tires on them, this system will not work on a leaf spring system, at least, not for long.

If you have what appears to be a squatting trailer where the fender is resting on the tire or very close then you have had a torsion axle failure. You are done, don't try to tow it home, disaster can happen!

Additional reading here on WW:

http://www.wakeworld.com/forum/showt...t=torsion+axle

http://www.wakeworld.com/forum/showt...t=torsion+axle

http://www.wakeworld.com/forum/showt...t=torsion+axle

and the best one

http://www.wakeworld.com/forum/showt...t=torsion+axle

I stole the pictures:

NORMAL
http://i168.photobucket.com/albums/u197/seeajgo/1.jpg

BROKEN
http://i168.photobucket.com/albums/u197/seeajgo/2.jpg

http://i168.photobucket.com/albums/u197/seeajgo/3.jpg

http://i168.photobucket.com/albums/u197/seeajgo/6.jpg

CLASSIC!
http://i168.photobucket.com/albums/u197/seeajgo/8.jpg