Re: JPOR: Ladder bar forces (warning)

["Brett Davis" <bdavis@xxxxxxxxxxxxx>]

Also noted, there is a much higher chance that if something breaks related to the ladder bar, it will probably be where it attaches to the axle since the forces are much larger there, but since this would not be catastrophic it wasn't really worth mentioning.

Brett Davis wrote:

> ****************Please Remember to snip your replies***************
> You make a good point except that when the ladder bar is employed the springs are taken out of the axle wrap business for the most part.  (sometimes the ladder and the springs actually do battle)
>
> When/if the shackle breaks, the axle will rotate a certain amount until the springs take up the force, and since this will be sudden, the axle will rotate more than usual.  The axle will rotate at least as much as it would normally without the ladder bar.
>
> Say the axle rotates, without the ladder bar, approx 10 degrees (fairly common).  At the end of a 3' ladder this is 6.25 inches.  Say that under shock loading when the shackle broke that the axle housing rotated 20 or 30 degrees (possible), that's up to 20" of movement, enough to do some damage.
>
> I am continually amazed at the under-engineered ladder bars and especially locating arms that I see on rigs, but not when I see them broken on the trails.  Maybe I am too conservative in my assumptions, but even using "traction limited" values the numbers are huge.
>
> Brett
>
> ssmith@ai.com wrote:
>
> > ****************Please Remember to snip your replies***************
> > I think that something that you guys aren't thinking about –
> >
> > First, I would guess that racecars are probably using coil springs.  This would cause the ladder bar to manage all the forces on the axle.  The leaf springs on 'most' Jeeps (CJ/YJ/etc) will limit the force/distance of the moving ladder bar.  It will also limit the stresses on the ladder bar itself.  When working, the springs and the ladder bar will be working together to limit axle wrap.  If the ladder bar should break, it won't be a free moving object - the leafs will limit its movement.
> >
> > I have mine made out of 1"x1" square tubing.  It is, I think, 3/16" thick (maybe 1/8, but I think 3/16).  I'm running a total of around 110:1 crawl (T18/4:1 D300/4.27) with a Ford 5.0 V8.  It has never bent.  I have run Die Trying, Patriot, Rusty Nail, Helldurado, etc...  I have had the weight of the Jeep on the ladder bar.  It is very strong.  I copied the design from someone else running a similar hp/torque setup.  Theirs has not bent/broken either.
> >
> > For the connection at the front, I used two category 2 tractor heims that I welded together to form a shackle that will rotate in all directions.  I welded a bracket to the original skid plate and reinforced the skid plate with angle iron.  Everything is holding up fine.  Also - the longer the ladder bar, the less stress on the actual shackle/heims/etc on the non-axle end.
> >
> > That being said - I'm not an engineer.  Just going by what I have seen and what I use.  And, it is always better to over engineer then to under engineer..
> >
> > Steve
> >
> > >
> > >From: JpCj74x4@aol.com
> > >Date: Mon, 12 Mar 2001 09:29:01 EST
> > >To: jeepoffroad@4x4wire.com
> > >Subject: Re: JPOR: Ladder bar forces (warning)
> > >
> > >****************Please Remember to snip your replies***************
> > >Brett,
> > > You make a very good point to safety here. I race cars on dirt and have seen
> > >a ladder bar break causing some serious damage. On this car the bar was
> > >located on the chassis near the driver, above the drive shaft. Between the
> > >driver and the bar was, oh, about .045" aluminum forming the cockpit. I guess
> > >the bar slammed down first breaking the driveshaft (which got into the
> > >cockpit a little) but when the ladder bar bounced back up it almost ripped
> > >thru 1 3/4" x .090 chassis.
> > >  I can just imagine what it would do to a rusted out tub and the back seat.
> > >
> > >Greg
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> --
> Brett Davis
>
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Brett Davis